1 Moogukinos

Inaugural Dissertation Abstract

1. Life and works

Immanuel Kant was born April 22, 1724 in Königsberg, near the southeastern shore of the Baltic Sea. Today Königsberg has been renamed Kaliningrad and is part of Russia. But during Kant's lifetime Königsberg was the capital of East Prussia, and its dominant language was German. Though geographically remote from the rest of Prussia and other German cities, Königsberg was then a major commercial center, an important military port, and a relatively cosmopolitan university town.[1]

Kant was born into an artisan family of modest means. His father was a master harness maker, and his mother was the daughter of a harness maker, though she was better educated than most women of her social class. Kant's family was never destitute, but his father's trade was in decline during Kant's youth and his parents at times had to rely on extended family for financial support.

Kant's parents were Pietist and he attended a Pietist school, the Collegium Fridericianum, from ages eight through fifteen. Pietism was an evangelical Lutheran movement that emphasized conversion, reliance on divine grace, the experience of religious emotions, and personal devotion involving regular Bible study, prayer, and introspection. Kant reacted strongly against the forced soul-searching to which he was subjected at the Collegium Fridericianum, in response to which he sought refuge in the Latin classics, which were central to the school's curriculum. Later the mature Kant's emphasis on reason and autonomy, rather than emotion and dependence on either authority or grace, may in part reflect his youthful reaction against Pietism. But although the young Kant loathed his Pietist schooling, he had deep respect and admiration for his parents, especially his mother, whose “genuine religiosity” he described as “not at all enthusiastic.” According to his biographer, Manfred Kuehn, Kant's parents probably influenced him much less through their Pietism than through their artisan values of “hard work, honesty, cleanliness, and independence,” which they taught him by example.[2]

Kant attended college at the University of Königsberg, known as the Albertina, where his early interest in classics was quickly superseded by philosophy, which all first year students studied and which encompassed mathematics and physics as well as logic, metaphysics, ethics, and natural law. Kant's philosophy professors exposed him to the approach of Christian Wolff (1679–1750), whose critical synthesis of the philosophy of G. W. Leibniz (1646–1716) was then very influential in German universities. But Kant was also exposed to a range of German and British critics of Wolff, and there were strong doses of Aristotelianism and Pietism represented in the philosophy faculty as well. Kant's favorite teacher was Martin Knutzen (1713–1751), a Pietist who was heavily influenced by both Wolff and the English philosopher John Locke (1632–1704). Knutzen introduced Kant to the work of Isaac Newton (1642–1727), and his influence is visible in Kant's first published work, Thoughts on the True Estimation of Living Forces (1747), which was a critical attempt to mediate a dispute in natural philosophy between Leibnizians and Newtonians over the proper measurement of force.

After college Kant spent six years as a private tutor to young children outside Königsberg. By this time both of his parents had died and Kant's finances were not yet secure enough for him to pursue an academic career. He finally returned to Königsberg in 1754 and began teaching at the Albertina the following year. For the next four decades Kant taught philosophy there, until his retirement from teaching in 1796 at the age of seventy-two.

Kant had a burst of publishing activity in the years after he returned from working as a private tutor. In 1754 and 1755 he published three scientific works — one of which, Universal Natural History and Theory of the Heavens (1755), was a major book in which, among other things, he developed what later became known as the nebular hypothesis about the formation of the solar system. Unfortunately, the printer went bankrupt and the book had little immediate impact. To secure qualifications for teaching at the university, Kant also wrote two Latin dissertations: the first, entitled Concise Outline of Some Reflections on Fire (1755), earned him the Magister degree; and the second, New Elucidation of the First Principles of Metaphysical Cognition (1755), entitled him to teach as an unsalaried lecturer. The following year he published another Latin work, The Employment in Natural Philosophy of Metaphysics Combined with Geometry, of Which Sample I Contains the Physical Monadology (1756), in hopes of succeeding Knutzen as associate professor of logic and metaphysics, though Kant failed to secure this position. Both the New Elucidation, which was Kant's first work concerned mainly with metaphysics, and the Physical Monadology further develop the position on the interaction of finite substances that he first outlined in Living Forces. Both works depart from Leibniz-Wolffian views, though not radically. The New Elucidation in particular shows the influence of Christian August Crusius (1715–1775), a German critic of Wolff.[3]

As an unsalaried lecturer at the Albertina Kant was paid directly by the students who attended his lectures, so he needed to teach an enormous amount and to attract many students in order to earn a living. Kant held this position from 1755 to 1770, during which period he would lecture an average of twenty hours per week on logic, metaphysics, and ethics, as well as mathematics, physics, and physical geography. In his lectures Kant used textbooks by Wolffian authors such as Alexander Gottlieb Baumgarten (1714–1762) and Georg Friedrich Meier (1718–1777), but he followed them loosely and used them to structure his own reflections, which drew on a wide range of ideas of contemporary interest. These ideas often stemmed from British sentimentalist philosophers such as David Hume (1711–1776) and Francis Hutcheson (1694–1747), some of whose texts were translated into German in the mid-1750's; and from the Swiss philosopher Jean-Jacques Rousseau (1712–1778), who published a flurry of works in the early 1760's. From early in his career Kant was a popular and successful lecturer. He also quickly developed a local reputation as a promising young intellectual and cut a dashing figure in Königsberg society.

After several years of relative quiet, Kant unleashed another burst of publications in 1762–1764, including five philosophical works. The False Subtlety of the Four Syllogistic Figures (1762) rehearses criticisms of Aristotelian logic that were developed by other German philosophers. The Only Possible Argument in Support of a Demonstration of the Existence of God (1762–3) is a major book in which Kant drew on his earlier work in Universal History and New Elucidation to develop an original argument for God's existence as a condition of the internal possibility of all things, while criticizing other arguments for God's existence. The book attracted several positive and some negative reviews. In 1762 Kant also submitted an essay entitled Inquiry Concerning the Distinctness of the Principles of Natural Theology and Morality to a prize competition by the Prussian Royal Academy, though Kant's submission took second prize to Moses Mendelssohn's winning essay (and was published with it in 1764). Kant's Prize Essay, as it is known, departs more significantly from Leibniz-Wolffian views than his earlier work and also contains his first extended discussion of moral philosophy in print. The Prize Essay draws on British sources to criticize German rationalism in two respects: first, drawing on Newton, Kant distinguishes between the methods of mathematics and philosophy; and second, drawing on Hutcheson, he claims that “an unanalysable feeling of the good” supplies the material content of our moral obligations, which cannot be demonstrated in a purely intellectual way from the formal principle of perfection alone (2:299).[4] These themes reappear in the Attempt to Introduce the Concept of Negative Magnitudes into Philosophy (1763), whose main thesis, however, is that the real opposition of conflicting forces, as in causal relations, is not reducible to the logical relation of contradiction, as Leibnizians held. In Negative Magnitudes Kant also argues that the morality of an action is a function of the internal forces that motivate one to act, rather than of the external (physical) actions or their consequences. Finally, Observations on the Feeling of the Beautiful and the Sublime (1764) deals mainly with alleged differences in the tastes of men and women and of people from different cultures. After it was published, Kant filled his own interleaved copy of this book with (often unrelated) handwritten remarks, many of which reflect the deep influence of Rousseau on his thinking about moral philosophy in the mid-1760's.

These works helped to secure Kant a broader reputation in Germany, but for the most part they were not strikingly original. Like other German philosophers at the time, Kant's early works are generally concerned with using insights from British empiricist authors to reform or broaden the German rationalist tradition without radically undermining its foundations. While some of his early works tend to emphasize rationalist ideas, others have a more empiricist emphasis. During this time Kant was striving to work out an independent position, but before the 1770's his views remained fluid.

In 1766 Kant published his first work concerned with the possibility of metaphysics, which later became a central topic of his mature philosophy. Dreams of a Spirit-Seer Elucidated by Dreams of Metaphysics, which he wrote soon after publishing a short Essay on Maladies of the Mind (1764), was occasioned by Kant's fascination with the Swedish visionary Emanuel Swedenborg (1688–1772), who claimed to have insight into a spirit world that enabled him to make a series of apparently miraculous predictions. In this curious work Kant satirically compares Swedenborg's spirit-visions to the belief of rationalist metaphysicians in an immaterial soul that survives death, and he concludes that philosophical knowledge of either is impossible because human reason is limited to experience. The skeptical tone of Dreams is tempered, however, by Kant's suggestion that “moral faith” nevertheless supports belief in an immaterial and immortal soul, even if it is not possible to attain metaphysical knowledge in this domain (2:373).

In 1770, at the age of forty-six, Kant was appointed to the chair in logic and metaphysics at the Albertina, after teaching for fifteen years as an unsalaried lecturer and working since 1766 as a sublibrarian to supplement his income. Kant was turned down for the same position in 1758. But later, as his reputation grew, he declined chairs in philosophy at Erlangen (1769) and Jena (1770) in hopes of obtaining one in Königsberg. After Kant was finally promoted, he gradually extended his repertoire of lectures to include anthropology (Kant's was the first such course in Germany and became very popular), rational theology, pedagogy, natural right, and even mineralogy and military fortifications. In order to inaugurate his new position, Kant also wrote one more Latin dissertation: Concerning the Form and Principles of the Sensible and Intelligible World (1770), which is known as the Inaugural Dissertation.

The Inaugural Dissertation departs more radically from both Wolffian rationalism and British sentimentalism than Kant's earlier work. Inspired by Crusius and the Swiss natural philosopher Johann Heinrich Lambert (1728–1777), Kant distinguishes between two fundamental powers of cognition, sensibility and understanding (intelligence), where the Leibniz-Wolffians regarded understanding (intellect) as the only fundamental power. Kant therefore rejects the rationalist view that sensibility is only a confused species of intellectual cognition, and he replaces this with his own view that sensibility is distinct from understanding and brings to perception its own subjective forms of space and time — a view that developed out of Kant's earlier criticism of Leibniz's relational view of space in Concerning the Ultimate Ground of the Differentiation of Directions in Space (1768). Moreover, as the title of the Inaugural Dissertation indicates, Kant argues that sensibility and understanding are directed at two different worlds: sensibility gives us access to the sensible world, while understanding enables us to grasp a distinct intelligible world. These two worlds are related in that what the understanding grasps in the intelligible world is the “paradigm” of “NOUMENAL PERFECTION,” which is “a common measure for all other things in so far as they are realities.” Considered theoretically, this intelligible paradigm of perfection is God; considered practically, it is “MORAL PERFECTION” (2:396). The Inaugural Dissertation thus develops a form of Platonism; and it rejects the view of British sentimentalists that moral judgments are based on feelings of pleasure or pain, since Kant now holds that moral judgments are based on pure understanding alone.

After 1770 Kant never surrendered the views that sensibility and understanding are distinct powers of cognition, that space and time are subjective forms of human sensibility, and that moral judgments are based on pure understanding (or reason) alone. But his embrace of Platonism in the Inaugural Dissertation was short-lived. He soon denied that our understanding is capable of insight into an intelligible world, which cleared the path toward his mature position in the Critique of Pure Reason (1781), according to which the understanding (like sensibility) supplies forms that structure our experience of the sensible world, to which human knowledge is limited, while the intelligible (or noumenal) world is strictly unknowable to us. Kant spent a decade working on the Critique of Pure Reason and published nothing else of significance between 1770 and 1781. But its publication marked the beginning of another burst of activity that produced Kant's most important and enduring works. Because early reviews of the Critique of Pure Reason were few and (in Kant's judgment) uncomprehending, he tried to clarify its main points in the much shorter Prolegomena to Any Future Metaphysics That Will Be Able to Come Forward as a Science (1783). Among the major books that rapidly followed are the Groundwork of the Metaphysics of Morals (1785), Kant's main work on the fundamental principle of morality; the Metaphysical Foundations of Natural Science (1786), his main work on natural philosophy in what scholars call his critical period (1781–1798); the second and substantially revised edition of the Critique of Pure Reason (1787); the Critique of Practical Reason (1788), a fuller discussion of topics in moral philosophy that builds on (and in some ways revises) the Groundwork; and the Critique of the Power of Judgment (1790), which deals with aesthetics and teleology. Kant also published a number of important essays in this period, including Idea for a Universal History With a Cosmopolitan Aim (1784) and Conjectural Beginning of Human History (1786), his main contributions to the philosophy of history; An Answer to the Question: What is Enlightenment? (1784), which broaches some of the key ideas of his later political essays; and What Does it Mean to Orient Oneself in Thinking? (1786), Kant's intervention in the pantheism controversy that raged in German intellectual circles after F. H. Jacobi (1743–1819) accused the recently deceased G. E. Lessing (1729–1781) of Spinozism.

With these works Kant secured international fame and came to dominate German philosophy in the late 1780's. But in 1790 he announced that the Critique of the Power of Judgment brought his critical enterprise to an end (5:170). By then K. L. Reinhold (1758–1823), whose Letters on the Kantian Philosophy (1786) popularized Kant's moral and religious ideas, had been installed (in 1787) in a chair devoted to Kantian philosophy at Jena, which was more centrally located than Königsberg and rapidly developing into the focal point of the next phase in German intellectual history. Reinhold soon began to criticize and move away from Kant's views. In 1794 his chair at Jena passed to J. G. Fichte, who had visited the master in Königsberg and whose first book, Attempt at a Critique of All Revelation (1792), was published anonymously and initially mistaken for a work by Kant himself. This catapulted Fichte to fame, but he too soon moved away from Kant and developed an original position quite at odds with Kant's, which Kant finally repudiated publicly in 1799 (12:370–371). Yet while German philosophy moved on to assess and respond to Kant's legacy, Kant himself continued publishing important works in the 1790's. Among these are Religion Within the Boundaries of Mere Reason (1793), which drew a censure from the Prussian King when Kant published the book after its second essay was rejected by the censor; The Conflict of the Faculties (1798), a collection of essays inspired by Kant's troubles with the censor and dealing with the relationship between the philosophical and theological faculties of the university; On the Common Saying: That May be Correct in Theory, But it is of No Use in Practice (1793), Toward Perpetual Peace (1795), and the Doctrine of Right, the first part of the Metaphysics of Morals (1797), Kant's main works in political philosophy; the Doctrine of Virtue, the second part of the Metaphysics of Morals (1797), a catalogue of duties that Kant had been planning for more than thirty years; and Anthropology From a Pragmatic Point of View (1798), based on Kant's anthropology lectures. Several other compilations of Kant's lecture notes from other courses were published later, but these were not prepared by Kant himself.

Kant retired from teaching in 1796. For nearly two decades he had lived a highly disciplined life focused primarily on completing his philosophical system, which began to take definite shape in his mind only in middle age. After retiring he came to believe that there was a gap in this system separating the metaphysical foundations of natural science from physics itself, and he set out to close this gap in a series of notes that postulate the existence of an ether or caloric matter. These notes, known as the Opus Postumum, remained unfinished and unpublished in Kant's lifetime, and scholars disagree on their significance and relation to his earlier work. It is clear, however, that these late notes show unmistakable signs of Kant's mental decline, which became tragically precipitous around 1800. Kant died February 12, 1804, just short of his eightieth birthday.

2. Kant's project in the Critique of Pure Reason

The main topic of the Critique of Pure Reason is the possibility of metaphysics, understood in a specific way. Kant defines metaphysics in terms of “the cognitions after which reason might strive independently of all experience,” and his goal in the book is to reach a “decision about the possibility or impossibility of a metaphysics in general, and the determination of its sources, as well as its extent and boundaries, all, however, from principles” (Axii. See also Bxiv; and 4:255–257). Thus metaphysics for Kant concerns a priori knowledge, or knowledge whose justification does not depend on experience; and he associates a priori knowledge with reason. The project of the Critique is to examine whether, how, and to what extent human reason is capable of a priori knowledge.

2.1 The crisis of the Enlightenment

To understand the project of the Critique better, let us consider the historical and intellectual context in which it was written.[5] Kant wrote the Critique toward the end of the Enlightenment, which was then in a state of crisis. Hindsight enables us to see that the 1780’s was a transitional decade in which the cultural balance shifted decisively away from the Enlightenment toward Romanticism, but of course Kant did not have the benefit of such hindsight.

The Enlightenment was a reaction to the rise and successes of modern science in the sixteenth and seventeenth centuries. The spectacular achievement of Newton in particular engendered widespread confidence and optimism about the power of human reason to control nature and to improve human life. One effect of this new confidence in reason was that traditional authorities were increasingly questioned. For why should we need political or religious authorities to tell us how to live or what to believe, if each of us has the capacity to figure these things out for ourselves? Kant expresses this Enlightenment commitment to the sovereignty of reason in the Critique:

Our age is the age of criticism, to which everything must submit. Religion through its holiness and legislation through its majesty commonly seek to exempt themselves from it. But in this way they excite a just suspicion against themselves, and cannot lay claim to that unfeigned respect that reason grants only to that which has been able to withstand its free and public examination (Axi).

Enlightenment is about thinking for oneself rather than letting others think for you, according to What is Enlightenment? (8:35). In this essay, Kant also expresses the Enlightenment faith in the inevitability of progress. A few independent thinkers will gradually inspire a broader cultural movement, which ultimately will lead to greater freedom of action and governmental reform. A culture of enlightenment is “almost inevitable” if only there is “freedom to make public use of one's reason in all matters” (8:36).

The problem is that to some it seemed unclear whether progress would in fact ensue if reason enjoyed full sovereignty over traditional authorities; or whether unaided reasoning would instead lead straight to materialism, fatalism, atheism, skepticism (Bxxxiv), or even libertinism and authoritarianism (8:146). The Enlightenment commitment to the sovereignty of reason was tied to the expectation that it would not lead to any of these consequences but instead would support certain key beliefs that tradition had always sanctioned. Crucially, these included belief in God, the soul, freedom, and the compatibility of science with morality and religion. Although a few intellectuals rejected some or all of these beliefs, the general spirit of the Enlightenment was not so radical. The Enlightenment was about replacing traditional authorities with the authority of individual human reason, but it was not about overturning traditional moral and religious beliefs.

Yet the original inspiration for the Enlightenment was the new physics, which was mechanistic. If nature is entirely governed by mechanistic, causal laws, then it may seem that there is no room for freedom, a soul, or anything but matter in motion. This threatened the traditional view that morality requires freedom. We must be free in order to choose what is right over what is wrong, because otherwise we cannot be held responsible. It also threatened the traditional religious belief in a soul that can survive death or be resurrected in an afterlife. So modern science, the pride of the Enlightenment, the source of its optimism about the powers of human reason, threatened to undermine traditional moral and religious beliefs that free rational thought was expected to support. This was the main intellectual crisis of the Enlightenment.

The Critique of Pure Reason is Kant's response to this crisis. Its main topic is metaphysics because, for Kant, metaphysics is the domain of reason – it is “the inventory of all we possess through pure reason, ordered systematically” (Axx) — and the authority of reason was in question. Kant's main goal is to show that a critique of reason by reason itself, unaided and unrestrained by traditional authorities, establishes a secure and consistent basis for both Newtonian science and traditional morality and religion. In other words, free rational inquiry adequately supports all of these essential human interests and shows them to be mutually consistent. So reason deserves the sovereignty attributed to it by the Enlightenment.

2.2 Kant's Copernican revolution in philosophy

To see how Kant attempts to achieve this goal in the Critique, it helps to reflect on his grounds for rejecting the Platonism of the Inaugural Dissertation. In a way the Inaugural Dissertation also tries to reconcile Newtonian science with traditional morality and religion, but its strategy is different from that of the Critique. According to the Inaugural Dissertation, Newtonian science is true of the sensible world, to which sensibility gives us access; and the understanding grasps principles of divine and moral perfection in a distinct intelligible world, which are paradigms for measuring everything in the sensible world. So on this view our knowledge of the intelligible world is a priori because it does not depend on sensibility, and this a priori knowledge furnishes principles for judging the sensible world because in some way the sensible world itself conforms to or imitates the intelligible world.

Soon after writing the Inaugural Dissertation, however, Kant expressed doubts about this view. As he explained in a February 21, 1772 letter to his friend and former student, Marcus Herz:

In my dissertation I was content to explain the nature of intellectual representations in a merely negative way, namely, to state that they were not modifications of the soul brought about by the object. However, I silently passed over the further question of how a representation that refers to an object without being in any way affected by it can be possible…. [B]y what means are these [intellectual representations] given to us, if not by the way in which they affect us? And if such intellectual representations depend on our inner activity, whence comes the agreement that they are supposed to have with objects — objects that are nevertheless not possibly produced thereby?…[A]s to how my understanding may form for itself concepts of things completely a priori, with which concepts the things must necessarily agree, and as to how my understanding may formulate real principles concerning the possibility of such concepts, with which principles experience must be in exact agreement and which nevertheless are independent of experience — this question, of how the faculty of understanding achieves this conformity with the things themselves, is still left in a state of obscurity. (10:130–131)

Here Kant entertains doubts about how a priori knowledge of an intelligible world would be possible. The position of the Inaugural Dissertation is that the intelligible world is independent of the human understanding and of the sensible world, both of which (in different ways) conform to the intelligible world. But, leaving aside questions about what it means for the sensible world to conform to an intelligible world, how is it possible for the human understanding to conform to or grasp an intelligible world? If the intelligible world is independent of our understanding, then it seems that we could grasp it only if we are passively affected by it in some way. But for Kant sensibility is our passive or receptive capacity to be affected by objects that are independent of us (2:392, A51/B75). So the only way we could grasp an intelligible world that is independent of us is through sensibility, which means that our knowledge of it could not be a priori. The pure understanding alone could at best enable us to form representations of an intelligible world. But since these intellectual representations would entirely “depend on our inner activity,” as Kant says to Herz, we have no good reason to believe that they conform to an independent intelligible world. Such a priori intellectual representations could well be figments of the brain that do not correspond to anything independent of the human mind. In any case, it is completely mysterious how there might come to be a correspondence between purely intellectual representations and an independent intelligible world.

Kant's strategy in the Critique is similar to that of the Inaugural Dissertation in that both works attempt to reconcile modern science with traditional morality and religion by relegating them to distinct sensible and intelligible worlds, respectively. But the Critique gives a far more modest and yet revolutionary account of a priori knowledge. As Kant's letter to Herz suggests, the main problem with his view in the Inaugural Dissertation is that it tries to explain the possibility of a priori knowledge about a world that is entirely independent of the human mind. This turned out to be a dead end, and Kant never again maintained that we can have a priori knowledge about an intelligible world precisely because such a world would be entirely independent of us. However, Kant's revolutionary position in the Critique is that we can have a priori knowledge about the general structure of the sensible world because it is not entirely independent of the human mind. The sensible world, or the world of appearances, is constructed by the human mind from a combination of sensory matter that we receive passively and a priori forms that are supplied by our cognitive faculties. We can have a priori knowledge only about aspects of the sensible world that reflect the a priori forms supplied by our cognitive faculties. In Kant's words, “we can cognize of things a priori only what we ourselves have put into them” (Bxviii). So according to the Critique, a priori knowledge is possible only if and to the extent that the sensible world itself depends on the way the human mind structures its experience.

Kant characterizes this new constructivist view of experience in the Critique through an analogy with the revolution wrought by Copernicus in astronomy:

Up to now it has been assumed that all our cognition must conform to the objects; but all attempts to find out something about them a priori through concepts that would extend our cognition have, on this presupposition, come to nothing. Hence let us once try whether we do not get farther with the problems of metaphysics by assuming that the objects must conform to our cognition, which would agree better with the requested possibility of an a priori cognition of them, which is to establish something about objects before they are given to us. This would be just like the first thoughts of Copernicus, who, when he did not make good progress in the explanation of the celestial motions if he assumed that the entire celestial host revolves around the observer, tried to see if he might not have greater success if he made the observer revolve and left the stars at rest. Now in metaphysics we can try in a similar way regarding the intuition of objects. If intuition has to conform to the constitution of the objects, then I do not see how we can know anything of them a priori; but if the object (as an object of the senses) conforms to the constitution of our faculty of intuition, then I can very well represent this possibility to myself. Yet because I cannot stop with these intuitions, if they are to become cognitions, but must refer them as representations to something as their object and determine this object through them, I can assume either that the concepts through which I bring about this determination also conform to the objects, and then I am once again in the same difficulty about how I could know anything about them a priori, or else I assume that the objects, or what is the same thing, the experience in which alone they can be cognized (as given objects) conforms to those concepts, in which case I immediately see an easier way out of the difficulty, since experience itself is a kind of cognition requiring the understanding, whose rule I have to presuppose in myself before any object is given to me, hence a priori, which rule is expressed in concepts a priori, to which all objects of experience must therefore necessarily conform, and with which they must agree. (Bxvi-xviii)

As this passage suggests, what Kant has changed in the Critique is primarily his view about the role and powers of the understanding, since he already held in the Inaugural Dissertation that sensibility contributes the forms of space and time — which he calls pure (or a priori) intuitions (2:397) — to our cognition of the sensible world. But the Critique claims that pure understanding too, rather than giving us insight into an intelligible world, is limited to providing forms — which he calls pure or a priori concepts — that structure our cognition of the sensible world. So now both sensibility and understanding work together to construct cognition of the sensible world, which therefore conforms to the a priori forms that are supplied by our cognitive faculties: the a priori intuitions of sensibility and the a priori concepts of the understanding. This account is analogous to the heliocentric revolution of Copernicus in astronomy because both require contributions from the observer to be factored into explanations of phenomena, although neither reduces phenomena to the contributions of observers alone.[6] The way celestial phenomena appear to us on earth, according to Copernicus, is affected by both the motions of celestial bodies and the motion of the earth, which is not a stationary body around which everything else revolves. For Kant, analogously, the phenomena of human experience depend on both the sensory data that we receive passively through sensibility and the way our mind actively processes this data according to its own a priori rules. These rules supply the general framework in which the sensible world and all the objects (or phenomena) in it appear to us. So the sensible world and its phenomena are not entirely independent of the human mind, which contributes its basic structure.

How does Kant's Copernican revolution in philosophy improve on the strategy of the Inaugural Dissertation for reconciling modern science with traditional morality and religion? First, it gives Kant a new and ingenious way of placing modern science on an a priori foundation. He is now in a position to argue that we can have a priori knowledge about the basic laws of modern science because those laws reflect the human mind's contribution to structuring our experience. In other words, the sensible world necessarily conforms to certain fundamental laws — such as that every event has a cause — because the human mind constructs it according to those laws. Moreover, we can identify those laws by reflecting on the conditions of possible experience, which reveals that it would be impossible for us to experience a world in which, for example, any given event fails to have a cause. From this Kant concludes that metaphysics is indeed possible in the sense that we can have a priori knowledge that the entire sensible world — not just our actual experience, but any possible human experience — necessarily conforms to certain laws. Kant calls this immanent metaphysics or the metaphysics of experience, because it deals with the essential principles that are immanent to human experience.

But, second, if “we can cognize of things a priori only what we ourselves have put into them,” then we cannot have a priori knowledge about things whose existence and nature are entirely independent of the human mind, which Kant calls things in themselves (Bxviii). In his words: “[F]rom this deduction of our faculty of cognizing a priori [...] there emerges a very strange result [...], namely that with this faculty we can never get beyond the boundaries of possible experience, [...and] that such cognition reaches appearances only, leaving the thing in itself as something actual for itself but uncognized by us” (Bxix-xx). That is, Kant's constructivist foundation for scientific knowledge restricts science to the realm of appearances and implies that a priori knowledge of things in themselves that transcend possible human experience — or transcendent metaphysics — is impossible. In the Critique Kant thus rejects the insight into an intelligible world that he defended in the Inaugural Dissertation, and he now claims that rejecting knowledge about things in themselves is necessary for reconciling science with traditional morality and religion. This is because he claims that belief in God, freedom, and immortality have a strictly moral basis, and yet adopting these beliefs on moral grounds would be unjustified if we could know that they were false. “Thus,” Kant says, “I had to deny knowledge in order to make room for faith” (Bxxx). Restricting knowledge to appearances and relegating God and the soul to an unknowable realm of things in themselves guarantees that it is impossible to disprove claims about God and the freedom or immortality of the soul, which moral arguments may therefore justify us in believing. Moreover, the determinism of modern science no longer threatens the freedom required by traditional morality, because science and therefore determinism apply only to appearances, and there is room for freedom in the realm of things in themselves, where the self or soul is located. We cannot know (theoretically) that we are free, because we cannot know anything about things in themselves. But there are especially strong moral grounds for the belief in human freedom, which acts as “the keystone” supporting other morally grounded beliefs (5:3–4). In this way, Kant replaces transcendent metaphysics with a new practical science that he calls the metaphysics of morals. It thus turns out that two kinds of metaphysics are possible: the metaphysics of experience (or nature) and the metaphysics of morals, both of which depend on Kant's Copernican revolution in philosophy.

3. Transcendental idealism

Perhaps the central and most controversial thesis of the Critique of Pure Reason is that human beings experience only appearances, not things in themselves; and that space and time are only subjective forms of human intuition that would not subsist in themselves if one were to abstract from all subjective conditions of human intuition. Kant calls this thesis transcendental idealism.[7] One of his best summaries of it is arguably the following:

We have therefore wanted to say that all our intuition is nothing but the representation of appearance; that the things that we intuit are not in themselves what we intuit them to be, nor are their relations so constituted in themselves as they appear to us; and that if we remove our own subject or even only the subjective constitution of the senses in general, then all constitution, all relations of objects in space and time, indeed space and time themselves would disappear, and as appearances they cannot exist in themselves, but only in us. What may be the case with objects in themselves and abstracted from all this receptivity of our sensibility remains entirely unknown to us. We are acquainted with nothing except our way of perceiving them, which is peculiar to us, and which therefore does not necessarily pertain to every being, though to be sure it pertains to every human being. We are concerned solely with this. Space and time are its pure forms, sensation in general its matter. We can cognize only the former a priori, i.e., prior to all actual perception, and they are therefore called pure intuition; the latter, however, is that in our cognition that is responsible for its being called a posteriori cognition, i.e., empirical intuition. The former adheres to our sensibility absolutely necessarily, whatever sort of sensations we may have; the latter can be very different. (A42/B59–60)[8]

Kant introduces transcendental idealism in the part of the Critique called the Transcendental Aesthetic, and scholars generally agree that for Kant transcendental idealism encompasses at least the following claims:

  • In some sense, human beings experience only appearances, not things in themselves.
  • Space and time are not things in themselves, or determinations of things in themselves that would remain if one abstracted from all subjective conditions of human intuition. [Kant labels this conclusion a) at A26/B42 and again at A32–33/B49. It is at least a crucial part of what he means by calling space and time transcendentally ideal (A28/B44, A35–36/B52)].
  • Space and time are nothing other than the subjective forms of human sensible intuition. [Kant labels this conclusion b) at A26/B42 and again at A33/B49–50].
  • Space and time are empirically real, which means that “everything that can come before us externally as an object” is in both space and time, and that our internal intuitions of ourselves are in time (A28/B44, A34–35/B51–51).

But scholars disagree widely on how to interpret these claims, and there is no such thing as the standard interpretation of Kant's transcendental idealism. Two general types of interpretation have been especially influential, however. This section provides an overview of these two interpretations, although it should be emphasized that much important scholarship on transcendental idealism does not fall neatly into either of these two camps.

3.1 The two-objects interpretation

The two-objects reading is the traditional interpretation of Kant's transcendental idealism. It goes back to the earliest review of the Critique — the so-called Göttingen review by Christian Garve (1742–1798) and J. G. Feder (1740–1821)[9] — and it was the dominant way of interpreting Kant's transcendental idealism during his own lifetime. It has been a live interpretive option since then and remains so today, although it no longer enjoys the dominance that it once did.[10]

According to the two-objects interpretation, transcendental idealism is essentially a metaphysical thesis that distinguishes between two classes of objects: appearances and things in themselves. Another name for this view is the two-worlds interpretation, since it can also be expressed by saying that transcendental idealism essentially distinguishes between a world of appearances and another world of things in themselves.

Things in themselves, on this interpretation, are absolutely real in the sense that they would exist and have whatever properties they have even if no human beings were around to perceive them. Appearances, on the other hand, are not absolutely real in that sense, because their existence and properties depend on human perceivers. Moreover, whenever appearances do exist, in some sense they exist in the mind of human perceivers. So appearances are mental entities or mental representations. This, coupled with the claim that we experience only appearances, makes transcendental idealism a form of phenomenalism on this interpretation, because it reduces the objects of experience to mental representations. All of our experiences – all of our perceptions of objects and events in space, even those objects and events themselves, and all non-spatial but still temporal thoughts and feelings – fall into the class of appearances that exist in the mind of human perceivers. These appearances cut us off entirely from the reality of things in themselves, which are non-spatial and non-temporal. Yet Kant's theory, on this interpretation, nevertheless requires that things in themselves exist, because they must transmit to us the sensory data from which we construct appearances. In principle we cannot know how things in themselves affect our senses, because our experience and knowledge is limited to the world of appearances constructed by and in the mind. Things in themselves are therefore a sort of theoretical posit, whose existence and role are required by the theory but are not directly verifiable.

The main problems with the two-objects interpretation are philosophical. Most readers of Kant who have interpreted his transcendental idealism in this way have been — often very — critical of it, for reasons such as the following:

First, at best Kant is walking a fine line in claiming on the one hand that we can have no knowledge about things in themselves, but on the other hand that we know that things in themselves exist, that they affect our senses, and that they are non-spatial and non-temporal. At worst his theory depends on contradictory claims about what we can and cannot know about things in themselves. This objection was influentially articulated by Jacobi, when he complained that “without that presupposition [of things in themselves] I could not enter into the system, but with it I could not stay within it” (Jacobi 1787, 336).

Second, even if that problem is surmounted, it has seemed to many that Kant's theory, interpreted in this way, implies a radical form of skepticism that traps each of us within the contents of our own mind and cuts us off from reality. Some versions of this objection proceed from premises that Kant rejects. One version maintains that things in themselves are real while appearances are not, and hence that on Kant's view we cannot have experience or knowledge of reality. But Kant denies that appearances are unreal: they are just as real as things in themselves but are in a different metaphysical class. Another version claims that truth always involves a correspondence between mental representations and things in themselves, from which it would follow that on Kant's view it is impossible for us to have true beliefs about the world. But just as Kant denies that things in themselves are the only (or privileged) reality, he also denies that correspondence with things in themselves is the only kind of truth. Empirical judgments are true just in case they correspond with their empirical objects in accordance with the a priori principles that structure all possible human experience. But the fact that Kant can appeal in this way to an objective criterion of empirical truth that is internal to our experience has not been enough to convince some critics that Kant is innocent of an unacceptable form of skepticism, mainly because of his insistence on our irreparable ignorance about things in themselves.

Third and finally, Kant's denial that things in themselves are spatial or temporal has struck many of his readers as incoherent. The role of things in themselves, on the two-object interpretation, is to affect our senses and thereby to provide the sensory data from which our cognitive faculties construct appearances within the framework of our a priori intuitions of space and time and a priori concepts such as causality. But if there is no space, time, change, or causation in the realm of things in themselves, then how can things in themselves affect us? Transcendental affection seems to involve a causal relation between things in themselves and our sensibility. If this is simply the way we unavoidably think about transcendental affection, because we can give positive content to this thought only by employing the concept of a cause, while it is nevertheless strictly false that things in themselves affect us causally, then it seems not only that we are ignorant of how things in themselves really affect us. It seems, rather, to be incoherent that things in themselves could affect us at all if they are not in space or time.

3.2 The two-aspects interpretation

The two-aspects reading attempts to interpret Kant's transcendental idealism in a way that enables it to be defended against at least some of these objections. On this view, transcendental idealism does not distinguish between two classes of objects but rather between two different aspects of one and the same class of objects. For this reason it is also called the one-world interpretation, since it holds that there is only one world in Kant's ontology, and that at least some objects in that world have two different aspects: one aspect that appears to us, and another aspect that does not appear to us. That is, appearances are aspects of the same objects that also exist in themselves. So, on this reading, appearances are not mental representations, and transcendental idealism is not a form of phenomenalism.[11]

There are at least two main versions of the two-aspects theory. One version treats transcendental idealism as a metaphysical theory according to which objects have two aspects in the sense that they have two sets of properties: one set of relational properties that appear to us and are spatial and temporal, and another set of intrinsic properties that do not appear to us and are not spatial or temporal (Langton 1998). This property-dualist interpretation faces epistemological objections similar to those faced by the two-objects interpretation, because we are in no better position to acquire knowledge about properties that do not appear to us than we are to acquire knowledge about objects that do not appear to us. Moreover, this interpretation also seems to imply that things in themselves are spatial and temporal, since appearances have spatial and temporal properties, and on this view appearances are the same objects as things in themselves. But Kant explicitly denies that space and time are properties of things in themselves.

A second version of the two-aspects theory departs more radically from the traditional two-objects interpretation by denying that transcendental idealism is at bottom a metaphysical theory. Instead, it interprets transcendental idealism as a fundamentally epistemological theory that distinguishes between two standpoints on the objects of experience: the human standpoint, from which objects are viewed relative to epistemic conditions that are peculiar to human cognitive faculties (namely, the a priori forms of our sensible intuition); and the standpoint of an intuitive intellect, from which the same objects could be known in themselves and independently of any epistemic conditions (Allison 2004). Human beings cannot really take up the latter standpoint but can form only an empty concept of things as they exist in themselves by abstracting from all the content of our experience and leaving only the purely formal thought of an object in general. So transcendental idealism, on this interpretation, is essentially the thesis that we are limited to the human standpoint, and the concept of a thing in itself plays the role of enabling us to chart the boundaries of the human standpoint by stepping beyond them in abstract (but empty) thought.

One criticism of this epistemological version of the two-aspects theory is that it avoids the objections to other interpretations by attributing to Kant a more limited project than the text of the Critique warrants. There are passages that support this reading.[12] But there are also many passages in both editions of the Critique in which Kant describes appearances as representations in the mind and in which his distinction between appearances and things in themselves is given not only epistemological but metaphysical significance.[13] It is unclear whether all of these texts admit of a single, consistent interpretation.

4. The transcendental deduction

The transcendental deduction is the central argument of the Critique of Pure Reason and one of the most complex and difficult texts in the history of philosophy. Given its complexity, there are naturally many different ways of interpreting the deduction.[14] This brief overview provides one perspective on some of its main ideas.

The transcendental deduction occurs in the part of the Critique called the Analytic of Concepts, which deals with the a priori concepts that, on Kant's view, our understanding uses to construct experience together with the a priori forms of our sensible intuition (space and time), which he discussed in the Transcendental Aesthetic. Kant calls these a priori concepts “categories,” and he argues elsewhere (in the so-called metaphysical deduction) that they include such concepts as substance and cause. The goal of the transcendental deduction is to show that we have a priori concepts or categories that are objectively valid, or that apply necessarily to all objects in the world that we experience. To show this, Kant argues that the categories are necessary conditions of experience, or that we could not have experience without the categories. In Kant's words:

[T]he objective validity of the categories, as a priori concepts, rests on the fact that through them alone is experience possible (as far as the form of thinking is concerned). For they then are related necessarily and a priori to objects of experience, since only by means of them can any object of experience be thought at all.

The transcendental deduction of all a priori concepts therefore has a principle toward which the entire investigation must be directed, namely this: that they must be recognized as a priori conditions of the possibility of experiences (whether of the intuition that is encountered in them, or of the thinking). Concepts that supply the objective ground of the possibility of experience are necessary just for that reason. (A93–94/B126)

The strategy Kant employs to argue that the categories are conditions of experience is the main source of both the obscurity and the ingenuity of the transcendental deduction. His strategy is to argue that the categories are necessary specifically for self-consciousness, for which Kant often uses the Leibnizian term “apperception.”

4.1 Self-consciousness

One way to approach Kant's argument is to contrast his view of self-consciousness with two alternative views that he rejects. Each of these views, both Kant's and those he rejects, can be seen as offering competing answers the question: what is the source of our sense of an ongoing and invariable self that persists throughout all the changes in our experience?

The first answer to this question that Kant rejects is that self-consciousness arises from some particular content being present in each of one’s representations. This material conception of self-consciousness, as we may call it, is loosely suggested by Locke’s account of personal identity. According to Locke, “it being the same consciousness that makes a Man be himself to himself, personal Identity depends on that only, whether it be annexed only to one individual Substance, or can be continued in a succession of several Substances” (Essay 2.27.10). What Locke calls “the same consciousness” may be understood as some representational content that is always present in my experience and that both identifies any experience as mine and gives me a sense of a continuous self by virtue of its continual presence in my experience. One problem with this view, Kant believes, is that there is no such representational content that is invariably present in experience, so the sense of an ongoing self cannot possibly arise from that non-existent content (what Locke calls “consciousness”) being present in each of one's representations. In Kant's words, self-consciousness “does not yet come about by my accompanying each representation with consciousness, but rather by my adding one representation to the other and being conscious of their synthesis. Therefore it is only because I can combine a manifold of given representations in one consciousness that it is possible for me to represent the identity of the consciousness in these representations” (B133). Here Kant claims, against the Lockean view, that self-consciousness arises from combining (or synthesizing) representations with one another regardless of their content. In short, Kant has a formal conception of self-consciousness rather than a material one. Since no particular content of my experience is invariable, self-consciousness must derive from my experience having an invariable form or structure, and consciousness of the identity of myself through all of my changing experiences must consist in awareness of the formal unity and law-governed regularity of my experience. The continuous form of my experience is the necessary correlate for my sense of a continuous self.

There are at least two possible versions of the formal conception of self-consciousness: a realist and an idealist version. On the realist version, nature itself is law-governed and we become self-conscious by attending to its law-governed regularities, which also makes this an empiricist view of self-consciousness. The idea of an identical self that persists throughout all of our experience, on this view, arises from the law-governed regularity of nature, and our representations exhibit order and regularity because reality itself is ordered and regular. But Kant rejects this view and embraces a conception of self-consciousness that is both formal and idealist. According to Kant, the formal structure of our experience, its unity and law-governed regularity, is an achievement of our cognitive faculties rather than a property of reality in itself. Our experience has a constant form because our mind constructs experience in a law-governed way. So self-consciousness, for Kant, consists in awareness of the mind's law-governed activity of synthesizing or combining sensible data to construct a unified experience. As he expresses it, “this unity of consciousness would be impossible if in the cognition of the manifold the mind could not become conscious of the identity of the function by means of which this manifold is synthetically combined into one cognition” (A108).

Kant argues for this formal idealist conception of self-consciousness, and against the formal realist view, on the grounds that “we can represent nothing as combined in the object without having previously combined it ourselves” (B130). In other words, even if reality in itself were law-governed, its laws could not simply migrate over to our mind or imprint themselves on us while our mind is entirely passive. We must exercise an active capacity to represent the world as combined or ordered in a law-governed way, because otherwise we could not represent the world as law-governed even if it were law-governed in itself. Moreover, this capacity to represent the world as law-governed must be a priori because it is a condition of self-consciousness, and we would already have to be self-conscious in order to learn from our experience that there are law-governed regularities in the world. So it is necessary for self-consciousness that we exercise an a priori capacity to represent the world as law-governed. But this would also be sufficient for self-consciousness if we could exercise our a priori capacity to represent the world as law-governed even if reality in itself were not law-governed. In that case, the realist and empiricist conception of self-consciousness would be false, and the formal idealist view would be true.

Kant's confidence that no empiricist account could possibly explain self-consciousness may be based on his assumption that the sense of self each of us has, the thought of oneself as identical throughout all of one's changing experiences, involves necessity and universality, which on his view are the hallmarks of the a priori. This assumption is reflected in what we may call Kant's principle of apperception: “The I think must be able to accompany all my representations; for otherwise something would be represented in me that could not be thought at all, which is as much as to say that the representation would either be impossible or else at least would be nothing for me” (B131–132).[15] Notice the claims about necessity and universality embodied in the words “must” and “all” here. Kant is saying that for a representation to count as mine, it must necessarily be accessible to conscious awareness in some (perhaps indirect) way: I must be able to accompany it with “I think....” All of my representations must be accessible to consciousness in this way (but they need not actually be conscious), because again that is simply what makes a representation count as mine. Self-consciousness for Kant therefore involves a priori knowledge about the necessary and universal truth expressed in this principle of apperception, and a priori knowledge cannot be based on experience.

Recently it has been argued that Kant developed this thread of his argument in the transcendental deduction after reading Johann Nicolaus Tetens (1736–1807) rather than simply through a direct encounter with Locke's texts (Tetens 1777, Kitcher 2011). On the subject of self-consciousness, Tetens was a follower of Locke and also engaged with Hume's arguments for rejecting a continuing self. So Kant's actual opponents in the deduction may have been Lockean and Humean positions as represented by Tetens, as well as rationalist views that Kant would have encountered directly in texts by Leibniz, Wolff, and some of their followers.

4.2 Objectivity and judgment

On the basis of this formal idealist conception of self-consciousness, Kant's argument (at least one central thread of it) moves through two more conditions of self-consciousness in order to establish the objective validity of the categories. The next condition is that self-consciousness requires me to represent an objective world distinct from my subjective representations - that is, distinct from my thoughts about and sensations of that objective world. Kant uses this connection between self-consciousness and objectivity to insert the categories into his argument.

In order to be self-conscious, I cannot be wholly absorbed in the contents of my perceptions but must distinguish myself from the rest of the world. But if self-consciousness is an achievement of the mind, then how does the mind achieve this sense that there is a distinction between the I that perceives and the contents of its perceptions? According to Kant, the mind achieves this by distinguishing representations that necessarily belong together from representations that are not necessarily connected but are merely associated in a contingent way. Consider Kant's example of the perception of a house (B162). Imagine a house that is too large to fit into your visual field from your vantage point near its front door. Now imagine that you walk around the house, successively perceiving each of its sides. Eventually you perceive the entire house, but not all at once, and you judge that each of your representations of the sides of the house necessarily belong together (as sides of one house) and that anyone who denied this would be mistaken. But now imagine that you grew up in this house and associate a feeling of nostalgia with it. You would not judge that representations of this house are necessarily connected with feelings of nostalgia. That is, you would not think that other people seeing the house for the first time would be mistaken if they denied that it is connected with nostalgia, because you recognize that this house is connected with nostalgia for you but not necessarily for everyone. Yet you distinguish this merely subjective connection from the objective connection between sides of the house, which is objective because the sides of the house necessarily belong together “in the object,” because this connection holds for everyone universally, and because it is possible to be mistaken about it. The point here is not that we must successfully identify which representations necessarily belong together and which are merely associated contingently, but rather that to be self-conscious we must at least make this general distinction between objective and merely subjective connections of representations.

At this point (at least in the second edition text) Kant introduces the key claim that judgment is what enables us to distinguish objective connections of representations that necessarily belong together from merely subjective and contingent associations: “[A] judgment is nothing other than the way to bring given cognitions to the objective unity of apperception. That is the aim of the copula is in them: to distinguish the objective unity of given representations from the subjective. For this word designates the relation of the representations to the original apperception and its necessary unity” (B141–142). Kant is speaking here about the mental act of judging that results in the formation of a judgment. Judging is an act of what Kant calls synthesis, which he defines as “the action of putting different representations together with each other and comprehending their manifoldness in one cognition” (A77/B103). In other words, to synthesize is in general to combine several representations into a single (more) complex representation, and to judge is specifically to combine concepts into a judgment — that is, to join a subject concept to a predicate concept by means of the copula, as in “the body is heavy” or “the house is four-sided.” Judgments need not be true, of course, but they always have a truth value (true or false) because they make claims to objective validity. When I say, by contrast, that “If I carry a body, I feel a pressure of weight,” or that “if I see this house, I feel nostalgia,” I am not making a judgment about the object (the body or the house) but rather I am expressing a subjective association that may apply only to me (B142).[16]

Kant's reference to the necessary unity of apperception or self-consciousness in the quotation above means (at least) that the action of judging is the way our mind achieves self-consciousness. We must represent an objective world in order to distinguish ourselves from it, and we represent an objective world by judging that some representations necessarily belong together. Moreover, recall from 4.1 that, for Kant, we must have an a priori capacity to represent the world as law-governed, because “we can represent nothing as combined (or connected) in the object without having previously combined it ourselves” (B130). It follows that objective connections in the world cannot simply imprint themselves on our mind. Rather, experience of an objective world must be constructed by exercising an a priori capacity to judge, which Kant calls the faculty of understanding (A80–81/B106). The understanding constructs experience by providing the a priori rules, or the framework of necessary laws, in accordance with which we judge representations to be objective. These rules are the pure concepts of the understanding or categories, which are therefore conditions of self-consciousness, since they are rules for judging about an objective world, and self-consciousness requires that we distinguish ourselves from an objective world.

Kant identifies the categories in what he calls the metaphysical deduction, which precedes the transcendental deduction.[17] Very briefly, since the categories are a priori rules for judging, Kant argues that an exhaustive table of categories can be derived from a table of the basic logical forms of judgments. For example, according to Kant the logical form of the judgment that “the body is heavy” would be singular, affirmative, categorical, and assertoric. But since categories are not mere logical functions but instead are rules for making judgments about objects or an objective world, Kant arrives at his table of categories by considering how each logical function would structure judgments about objects (within our spatio-temporal forms of intuition). For example, he claims that categorical judgments express a logical relation between subject and predicate that corresponds to the ontological relation between substance and accident; and the logical form of a hypothetical judgment expresses a relation that corresponds to cause and effect. Taken together with this argument, then, the transcendental deduction argues that we become self-conscious by representing an objective world of substances that interact according to causal laws.

4.3 The law-giver of nature

The final condition of self-consciousness that Kant adds to the preceding conditions is that our understanding must cooperate with sensibility to construct one, unbounded, and unified space-time to which all of our representations may be related.

To see why this further condition is required, consider that so far we have seen why Kant holds that we must represent an objective world in order to be self-conscious, but we could represent an objective world even if it were not possible to relate all of our representations to this objective world. For all that has been said so far, we might still have unruly representations that we cannot relate in any way to the objective framework of our experience. On Kant's view, this would be a problem because, as we have seen, he holds that self-consciousness involves universality and necessity: according to his principle of apperception, “the I think must be able to accompany all my representations” (B131). Yet if, on the one hand, I had representations that I could not relate in some way to an objective world, then I could not accompany those representations with “I think” or recognize them as my representations, because I can say “I think…” about any given representation only by relating it to an objective world, according to the argument just discussed. So I must be able to relate any given representation to an objective world in order for it to count as mine. On the other hand, self-consciousness would also be impossible if I represented multiple objective worlds, even if I could relate all of my representations to some objective world or other. In that case, I could not become conscious of an identical self that has, say, representation 1 in space-time A and representation 2 in space-time B. It may be possible to imagine disjointed spaces and times, but it is not possible to represent them as objectively real. So self-consciousness requires that I can relate all of my representations to a single objective world.

The reason why I must represent this one objective world by means of a unified and unbounded space-time is that, as Kant argued in the Transcendental Aesthetic, space and time are the pure forms of human intuition. If we had different forms of intuition, then our experience would still have to constitute a unified whole in order for us to be self-conscious, but this would not be a spatio-temporal whole. Given that space and time are our forms of intuition, however, our understanding must still cooperate with sensibility to construct a spatio-temporal whole of experience because, once again, “we can represent nothing as combined in the object without having previously combined it ourselves,” and “all combination [...] is an action of the understanding” (B130). So Kant distinguishes between space and time as pure forms of intuition, which belong solely to sensibility; and the formal intuitions of space and time (or space-time), which are unified by the understanding (B160–161). These formal intuitions are the spatio-temporal whole within which our understanding constructs experience in accordance with the categories.[18]

The most important implication of Kant's claim that the understanding constructs a single whole of experience to which all of our representations can be related is that, since he defines nature “regarded materially” as “the sum total of all appearances” and he has argued that the categories are objectively valid of all possible appearances, on his view it follows that our categories are the source of the fundamental laws of nature “regarded formally” (B163, 165). So Kant concludes on this basis that the understanding is the true law-giver of nature. In his words: “all appearances in nature, as far as their combination is concerned, stand under the categories, on which nature (considered merely as nature in general) depends, as the original ground of its necessary lawfulness (as nature regarded formally)” (ibid.). Or more strongly: “we ourselves bring into the appearances that order and regularity that we call nature, and moreover we would not be able to find it there if we, or the nature of our mind, had not originally put it there. [...] The understanding is thus not merely a faculty for making rules through the comparison of the appearances: it is itself the legislation for nature, i.e., without understanding there would not be any nature at all” (A125–126).

5. Morality and freedom

Having examined two central parts of Kant's positive project in theoretical philosophy from the Critique of Pure Reason, transcendental idealism and the transcendental deduction, let us now turn to his practical philosophy in the Critique of Practical Reason. Since Kant's philosophy is deeply systematic, this section begins with a preliminary look at how his theoretical and practical philosophy fit together (see also section 7).

5.1 Theoretical and practical autonomy

The fundamental idea of Kant's philosophy is human autonomy. So far we have seen this in Kant's constructivist view of experience, according to which our understanding is the source of the general laws of nature. “Autonomy” literally means giving the law to oneself, and on Kant's view our understanding provides laws that constitute the a priori framework of our experience. Our understanding does not provide the matter or content of our experience, but it does provide the basic formal structure within which we experience any matter received through our senses. Kant's central argument for this view is the transcendental deduction, according to which it is a condition of self-consciousness that our understanding constructs experience in this way. So we may call self-consciousness the highest principle of Kant's theoretical philosophy, since it is (at least) the basis for all of our a priori knowledge about the structure of nature.

Kant's moral philosophy is also based on the idea of autonomy. He holds that there is a single fundamental principle of morality, on which all specific moral duties are based. He calls this moral law (as it is manifested to us) the categorical imperative (see 5.4). The moral law is a product of reason, for Kant, while the basic laws of nature are products of our understanding. There are important differences between the senses in which we are autonomous in constructing our experience and in morality. For example, Kant regards understanding and reason as different cognitive faculties, although he sometimes uses “reason” in a wide sense to cover both.[19] The categories and therefore the laws of nature are dependent on our specifically human forms of intuition, while reason is not. The moral law does not depend on any qualities that are peculiar to human nature but only on the nature of reason as such, although its manifestation to us as a categorical imperative (as a law of duty) reflects the fact that the human will is not necessarily determined by pure reason but is also influenced by other incentives rooted in our needs and inclinations; and our specific duties deriving from the categorical imperative do reflect human nature and the contingencies of human life. Despite these differences, however, Kant holds that we give the moral law to ourselves, just as we also give the general laws of nature to ourselves, though in a different sense. Moreover, we each necessarily give the same moral law to ourselves, just as we each construct our experience in accordance with the same categories. To summarize:

  • Theoretical philosophy is about how the world is (A633/B661). Its highest principle is self-consciousness, on which our knowledge of the basic laws of nature is based. Given sensory data, our understanding constructs experience according to these a priori laws.
  • Practical philosophy is about how the world ought to be (ibid., A800–801/B828–829). Its highest principle is the moral law, from which we derive duties that command how we ought to act in specific situations. Kant also claims that reflection on our moral duties and our need for happiness leads to the thought of an ideal world, which he calls the highest good (see section 6). Given how the world is (theoretical philosophy) and how it ought to be (practical philosophy), we aim to make the world better by constructing or realizing the highest good.

So both parts of Kant's philosophy are about autonomously constructing a world, but in different senses. In theoretical philosophy, we use our categories and forms of intuition to construct a world of experience or nature. In practical philosophy, we use the moral law to construct the idea of a moral world or a realm of ends that guides our conduct (4:433), and ultimately to transform the natural world into the highest good. Finally, transcendental idealism is the framework within which these two parts of Kant's philosophy fit together (20:311). Theoretical philosophy deals with appearances, to which our knowledge is strictly limited; and practical philosophy deals with things in themselves, although it does not give us knowledge about things in themselves but only provides rational justification for certain beliefs about them for practical purposes.

To understand Kant's arguments that practical philosophy justifies certain beliefs about things in themselves, it is necessary to see them in the context of his criticism of German rationalist metaphysics. The three traditional topics of Leibniz-Wolffian special metaphysics were rational psychology, rational cosmology, and rational theology, which dealt, respectively, with the human soul, the world-whole, and God. In the part of the Critique of Pure Reason called the Transcendental Dialectic, Kant argues against the Leibniz-Wolffian view that human beings are capable of a priori knowledge in each of these domains, and he claims that the errors of Leibniz-Wolffian metaphysics are due to an illusion that has its seat in the nature of human reason itself. According to Kant, human reason necessarily produces ideas of the soul, the world-whole, and God; and these ideas unavoidably produce the illusion that we have a priori knowledge about transcendent objects corresponding to them. This is an illusion, however, because in fact we are not capable of a priori knowledge about any such transcendent objects. Nevertheless, Kant attempts to show that these illusory ideas have a positive, practical use. He thus reframes Leibniz-Wolffian special metaphysics as a practical science that he calls the metaphysics of morals. On Kant's view, our ideas of the soul, the world-whole, and God provide the content of morally justified beliefs about human immortality, human freedom, and the existence of God, respectively; but they are not proper objects of speculative knowledge.[20]

5.2 Freedom

The most important belief about things in themselves that Kant thinks only practical philosophy can justify concerns human freedom. Freedom is important because, on Kant's view, moral appraisal presupposes that we are free in the sense that we have the ability to do otherwise. To see why, consider Kant's example of a man who commits a theft (5:95ff.). Kant holds that in order for this man's action to be morally wrong, it must have been within his control in the sense that it was within his power at the time not to have committed the theft. If this was not within his control at the time, then, while it may be useful to punish him in order to shape his behavior or to influence others, it nevertheless would not be correct to say that his action was morally wrong. Moral rightness and wrongness apply only to free agents who control their actions and have it in their power, at the time of their actions, either to act rightly or not. According to Kant, this is just common sense.

On these grounds, Kant rejects a type of compatibilism that he calls the “comparative concept of freedom” and associates with Leibniz (5:96–97). (Note that Kant has a specific type of compatibilism in mind, which I will refer to simply as “compatibilism,” although there may be other types of compatibilism that do not fit Kant's characterization of that view). On the compatibilist view, as Kant understands it, I am free whenever the cause of my action is within me. So I am unfree only when something external to me pushes or moves me, but I am free whenever the proximate cause of my body's movement is internal to me as an “acting being” (5:96). If we distinguish between involuntary convulsions and voluntary bodily movements, then on this view free actions are just voluntary bodily movements. Kant ridicules this view as a “wretched subterfuge” that tries to solve an ancient philosophical problem “with a little quibbling about words” (ibid.). This view, he says, assimilates human freedom to “the freedom of a turnspit,” or a projectile in flight, or the motion of a clock's hands (5:96–97). The proximate causes of these movements are internal to the turnspit, the projectile, and the clock at the time of the movement. This cannot be sufficient for moral responsibility.

Why not? The reason, Kant says, is ultimately that the causes of these movements occur in time. Return to the theft example. A compatibilist would say that the thief's action is free because its proximate cause is inside him, and because the theft was not an involuntary convulsion but a voluntary action. The thief decided to commit the theft, and his action flowed from this decision. According to Kant, however, if the thief's decision is a natural phenomenon that occurs in time, then it must be the effect of some cause that occurred in a previous time. This is an essential part of Kant's Newtonian worldview and is grounded in the a priori laws (specifically, the category of cause and effect) in accordance with which our understanding constructs experience: every event has a cause that begins in an earlier time. If that cause too was an event occurring in time, then it must also have a cause beginning in a still earlier time, etc. All natural events occur in time and are thoroughly determined by causal chains that stretch backwards into the distant past. So there is no room for freedom in nature, which is deterministic in a strong sense.

The root of the problem, for Kant, is time. Again, if the thief's choice to commit the theft is a natural event in time, then it is the effect of a causal chain extending into the distant past. But the past is out of his control now, in the present. Once the past is past, he can't change it. On Kant's view, that is why his actions would not be in his control in the present if they are determined by events in the past. Even if he could control those past events in the past, he cannot control them now. But in fact past events were not in his control in the past either if they too were determined by events in the more distant past, because eventually the causal antecedents of his action stretch back before his birth, and obviously events that occurred before his birth were not in his control. So if the thief's choice to commit the theft is a natural event in time, then it is not now and never was in his control, and he could not have done otherwise than to commit the theft. In that case, it would be a mistake to hold him morally responsible for it.

Compatibilism, as Kant understands it, therefore locates the issue in the wrong place. Even if the cause of my action is internal to me, if it is in the past — for example, if my action today is determined by a decision I made yesterday, or from the character I developed in childhood — then it is not within my control now. The real issue is not whether the cause of my action is internal or external to me, but whether it is in my control now. For Kant, however, the cause of my action can be within my control now only if it is not in time. This is why Kant thinks that transcendental idealism is the only way to make sense of the kind of freedom that morality requires. For transcendental idealism allows that the cause of my action may be a thing in itself outside of time: namely, my noumenal self, which is free because it is not part of nature. No matter what kind of character I have developed or what external influences act on me, on Kant's view all of my intentional, voluntary actions are immediate effects of my noumenal self, which is causally undetermined (5:97–98). My noumenal self is an uncaused cause outside of time, which therefore is not subject to the deterministic laws of nature in accordance with which our understanding constructs experience.

Many puzzles arise on this picture that Kant does not resolve. For example, if my understanding constructs all appearances in my experience of nature, not only appearances of my own actions, then why am I responsible only for my own actions but not for everything that happens in the natural world? Moreover, if I am not alone in the world but there are many noumenal selves acting freely and incorporating their free actions into the experience they construct, then how do multiple transcendentally free agents interact? How do you integrate my free actions into the experience that your understanding constructs?[21] In spite of these unsolved puzzles, Kant holds that we can make sense of moral appraisal and responsibility only by thinking about human freedom in this way, because it is the only way to prevent natural necessity from undermining both.

Finally, since Kant invokes transcendental idealism to make sense of freedom, interpreting his thinking about freedom leads us back to disputes between the two-objects and two-aspects interpretations of transcendental idealism. On the face of it, the two-objects interpretation seems to make better sense of Kant's view of transcendental freedom than the two-aspects interpretation. If morality requires that I am transcendentally free, then it seems that my true self, and not just an aspect of my self, must be outside of time, according to Kant's argument. But applying the two-objects interpretation to freedom raises problems of its own, since it involves making a distinction between noumenal and phenomenal selves that does not arise on the two-aspects view. If only my noumenal self is free, and freedom is required for moral responsibility, then my phenomenal self is not morally responsible. But how are my noumenal and phenomenal selves related, and why is punishment inflicted on phenomenal selves? It is unclear whether and to what extent appealing to Kant's theory of freedom can help to settle disputes about the proper interpretation of transcendental idealism, since there are serious questions about the coherence of Kant's theory on either interpretation.

5.3 The fact of reason

Can we know that we are free in this transcendental sense? Kant's response is tricky. On the one hand, he distinguishes between theoretical knowledge and morally justified belief (A820–831/B848–859). We do not have theoretical knowledge that we are free or about anything beyond the limits of possible experience, but we are morally justified in believing that we are free in this sense. On the other hand, Kant also uses stronger language than this when discussing freedom. For example, he says that “among all the ideas of speculative reason freedom is the only one the possibility of which we know a priori, though without having any insight into it, because it is the condition of the moral law, which we do know.” In a footnote to this passage, Kant explains that we know freedom a priori because “were there no freedom, the moral law would not be encountered at all in ourselves,” and on Kant's view everyone does encounter the moral law a priori (5:4). For this reason, Kant claims that the moral law “proves” the objective, “though only practical, undoubted reality” of freedom (5:48–49). So Kant wants to say that we do have knowledge of the reality of freedom, but that this is practical knowledge of a practical reality, or cognition “only for practical purposes,” by which he means to distinguish it from theoretical knowledge based on experience or reflection on the conditions of experience (5:133). Our practical knowledge of freedom is based instead on the moral law. The difference between Kant's stronger and weaker language seems mainly to be that his stronger language emphasizes that our belief or practical knowledge about freedom is unshakeable and that it in turn provides support for other morally grounded beliefs in God and the immortality of the soul.

Kant calls our consciousness of the moral law, our awareness that the moral law binds us or has authority over us, the “fact of reason” (5:31–32, 42–43, 47, 55). So, on his view, the fact of reason is the practical basis for our belief or practical knowledge that we are free. Kant insists that this moral consciousness is “undeniable,” “a priori,” and “unavoidable” (5:32, 47, 55). Every human being has a conscience, a common sense grasp of morality, and a firm conviction that he or she is morally accountable. We may have different beliefs about the source of morality's authority — God, social convention, human reason. We may arrive at different conclusions about what morality requires in specific situations. And we may violate our own sense of duty. But we all have a conscience, and an unshakeable belief that morality applies to us. According to Kant, this belief cannot and does not need to be justified or “proved by any deduction” (5:47). It is just a ground-level fact about human beings that we hold ourselves morally accountable. But Kant is making a normative claim here as well: it is also a fact, which cannot and does not need to be justified, that we are morally accountable, that morality does have authority over us. Kant holds that philosophy should be in the business of defending this common sense moral belief, and that in any case it could never prove or disprove it (4:459).

De Mundi Sensibilis atque Intelligibilis Forma et Principiis

Dissertation on the Form and Principles of the Sensible and the Intelligible World



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As the analysis of a substantial composite terminates only in a part which is not a whole, that is, in a simple part, so synthesis terminates only in a whole which is not a part, that is, the world.

In this exposition of the underlying concept I have had regard not only to the marks pertaining to the distinct cognition of the object, but somewhat also to the two-fold genesis of the concept from the nature of the mind, which, being serviceable to a method of deeper metaphysical insight, by way of example appears to me not a little commendable. For it is one thing, the parts being given, to conceive the composition of the whole by an abstract notion of the intellect, and another thing to follow out this general notion considered as a problem of the reason by the cognitive sensuous faculty, that is, to represent it to one’s self in the concrete by a distinct intuition. The former is done through the class concept by composition, as several things are contained either under it or mutually, and hence by intellectual and universal ideas. The latter rests on the conditions of time, inasmuch as the concept of a composite is possible genetically, that is by synthesis, by the successive union of part to part, and falls under the laws of intuition. Similarly, a substantial composite being given, we easily attain to the idea of the simple parts by the general removal of the intellectual notion of composition; for what remains after the removal of conjunction are the simple parts. But according to the laws of intuitive cognition this is not done, that is, all composition is not removed, except by a regress from the given whole to any possible parts whatsoever—in other words, by an analysis again resting on the condition of time.[1] But since in order to a composite a multiplicity, in order to a whole, the allness, of parts is required, neither the analysis nor the synthesis will be complete; hence neither by the former will the concept of the simple part emerge, nor by the latter the concept of the whole, unless either can be gone through within a time that is finite and assignable.

But since in a continuous quantity the regress from the whole to assignable parts, and in an infinite quantity the progress from the parts to the given whole are endless, complete analysis in the one and complete synthesis in the other direction are impossible; hence neither the whole in the first case as to composition, nor the composite in the latter case as to totality can be thought completely in accordance with the laws of intuition. Unthinkable and impossible being vulgarly deemed to have the same meaning, it is plain why the concepts of the continuous as well as that of the infinite are rejected by most men as concepts whose representation according to the laws of intuitive cognition is impossible. Although I do not here champion these notions, especially not the first, which are considered exploded by many schools, still the following reminder is of the greatest moment. Those who use so perverse an argumentation have fallen into a grave error.[2] For whatever is repugnant to the laws of the intellect and reason is of course impossible, but that which being the object of pure reason does merely not fall under the laws of intuitive cognition is not so. For here the disagreement between the sensuous and the intellectual faculties, whose natures I shall presently explain, indicates nothing except that the abstract ideas which the mind has received from the intellect can often not be followed out in the concrete and converted into intuitions. This subjective difficulty generally feigns some objective repugnance and easily deceives the incautious, the limits by which the human mind is circumscribed being taken for those by which the essence of things themselves is contained.

Furthermore, as the argument from intellectual reasonings easily shows that substantial composites being given, whether by the testimony of the senses or otherwise, the simple parts and the world are also given, so does our definition point out causes contained in the nature of the subject why the notion of a world should not seem merely arbitrary and made up, as in mathematics, only for the sake of the deducible consequences. The mind intent upon resolving as well as compounding the concept of a composite demands and presumes boundaries in which it may acquiesce in the former as well as in the latter direction.

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In defining the World the following points require attention:

I. Matter (in the transcendental sense), that is, the parts which are here assumed to be substances. We might plainly be regardless of coincidence between our definition and the meaning of the common word, the question being, so to speak, of a problem arising in accordance with the laws of reasoning, namely, how several substances may coalesce into one, and on what condition rests this one’s being no part of another. But the force of the word World, as commonly used, of itself falls in with us. For no one will attribute accidents to the World as parts, but as determinations, states; hence the so-called world of the ego, unrestrained by the single substance and its accidents, is not very appositely called a World, unless, perhaps, an imaginary one. For the same reason it is not permissible to refer the successive series—namely, of states—as a part to the mundane whole; for modifications are not parts, but consequences of the subject. Finally, as to the nature of the substances constituting the world, I have not here called into debate whether they be contingent or necessary, nor do I hide such a determination unproved in the definition in order subsequently, as is sometimes done, to draw it thence by some specious argumentation. But I shall show further on that their contingency can be amply concluded from the conditions here posited.

II. Form, which consists in the co-ordination of the substances, not in their subordination. For co-ordinates are to be regarded as mutual complements to a whole, subordinates as effect and cause, or generally, as principle and consequence. The former relation is reciprocal and homonymous, any correlate in respect to any other being considered as at once determining and determined. The latter is heteronymous; on the one hand dependence only, causality on the other. This co-ordination is conceived as real and objective, not as ideal, and resting in the mere pleasure of a subject making up a whole by the summation of any multiplicity whatever. For the grasping of several things can by no contrivance be made a whole of representation, nor, for that reason, a representation of the whole. Therefore, if there be any totals of substances connected by no bond, a grasping of them together, the mind forcing the multiplicity into ideal oneness, will be called nothing more than a plurality of worlds comprehended in a single thought. But the connection constituting the essential form of a world is looked upon as the principle of the possible influences of the substances composing that world. For an actual influence pertains not to essence but to state, and the transitive forces, the causes of the influences, suppose some principle by which it is possible that the states of several things in other respects existing independently of each other are mutually related as consequences, which principle being abandoned, the possibility of transitive force in a world is an illicit assumption. And, furthermore, this form essential to the world is on that account immutable, and exposed to no vicissitude whatever. It is so in the first place for a logical reason, since any change supposes the identity of the subject with determinations succeeding one another in turn. Hence the world, remaining the same world through all the states succeeding one another, preserves the same fundamental form. For it does not suffice to the identity of the whole that all the parts be identical, the identity of characteristic composition is required also. But it follows especially from a real cause. For the nature of the world, which is the primary inner principle of whatever variable determinations may pertain to its state, never by any possibility being opposite to itself, is naturally, that is, by itself, immutable; hence there is given in any world whatever some form ascribable to its nature, constant and invariable, as the perennial principle of any contingent and transitory form pertaining to the state of the world. They who hold this disquisition superfluous are confuted by the concepts of space and time, conditions, as it were, given by their very own selves and primitive, by whose aid, that is to say, without any other principle, it is not only possible but necessary for several actual things to be regarded as reciprocally parts constituting a whole. But I shall show presently that these are plainly not rational notions, nor the bonds which they form objective ideas, but phenomena; and that though they witness, to be sure, some principle which is the common universal bond, it is not set forth by them.

III. Universality, which is the absolute allness of the appertaining parts. For, regard being had to any given composite, though it may be besides a part of another, still there always obtains a certain comparative allness, namely, that of the parts belonging to it as a particular quantity. But in this case whatsoever things are regarded as mutually parts of whatsoever whole, are understood to be conjointly posited. This absolute totality, apparently an everyday and perfectly obvious concept, especially when, as happens in the definition, it is enunciated negatively, when canvassed thoroughly becomes the crucial test of the philosopher. For it is scarce conceivable how the inexhaustible series of the states of the universe succeeding one another eternally be reducible to a whole comprehending all changes whatsoever. Since it is necessary to very infinitude to be without end, and hence no successive series is given but what is the part of another, completeness or absolute totality is by parity of reasoning plainly excluded. For although the notion of a part can be taken in a universal sense, and although everything contained under this notion, if regarded as posited in the same series, constitutes unity, yet the concept of the whole appears to exact their all being taken simultaneously, which in the case given is impossible. For, although to the whole series nothing succeeds, there is given in the succession no posited series to which nothing succeeds, unless it be the last. There will, then, in eternity be something which is last, which is absurd. Perhaps some may think that the difficulty which besets a successive infinite is absent from a simultaneous infinite, for the reason that apparently simultaneity plainly professes to embrace all at the same time. But, if the simultaneous infinite be admitted, the successive infinite also will have to be conceded, and the negation of the latter cancels the former. For the simultaneous infinite offers matters everlastingly inexhaustible to a successive progress in infinitum through its innumerable parts, which numberless series actually being given in the simultaneous infinite, a series though inexhaustible by successive addition could be given as a whole. In solution of the perplexing problem note; that both the successive and the simultaneous co-ordination of several things, since they rest upon the concept of time, do not pertain to the intellectual concept of a whole, but only to the conditions of sensuous intuition; hence though not sensuously conceivable, they do not on that score cease being intellectual concepts. For in order to the latter it suffices that co-ordinates be given, no matter how, and that they be thought of as all pertaining to a unit.



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Sensibility is the receptivity of a subject by which it is possible for its representative state to be affected in a certain way by the presence of some object. Intelligence, rationality, is the faculty of a subject by which it is able to represent to itself what by its quality cannot enter the senses. The object of sensibility is sensuous; what contains nothing but what is knowable by the intellect is intelligible. In the older schools the former was called phenomenon, the latter noumenon. To the extent to which knowledge is subject to the laws of sensuousness it is sensuous; to the extent to which it is subject to the laws of intelligence it is intellectual or rational.

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Since whatever is in sensuous knowledge depends upon the subject’s peculiar nature, as the latter is capable of receiving some modification or other from the presence of objects which on account of subjective variety may be different in different subjects, whilst whatever knowledge is exempt from such subjective condition regards the object only, it is plain that what is sensuously thought is the representation of things as they appear, while the intellectual presentations are the representations of things as they are. Now there is in sense representation something which may be called the matter, namely, the sensation, and in addition to this something which may be called the form, namely, the appearance of the sensible things, showing forth to what extent a natural law of the mind co-ordinates the variety of sensuous affections. Furthermore, as the sensation constituting the matter of sensuous representations argues, to be sure, the presence of something sensible, but depends as to quality on the nature of the subject, as the latter is modifiable by the object; exactly so does the form of that representation witness certainly some reference or relation among the sensuous percepts, but itself is not, as it were, the shadowing forth or outlining of the object, but only a certain law inherent in the mind for co-ordinating among themselves sensuous percepts arising from the presence of the object. For by form or appearance the objects do not strike the sense, hence in order that various sense-affecting objects may coalesce into some whole of representation, there is need of an inner principle of the mind by which, in accordance with stable and innate laws, that variety shall take on some appearance.

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To sensual cognition then pertains both the matter which is sensation and by which the knowledge is said to be sensual, and the form by which, even though we find it without any sensation, the representations are called sensuous. On the other hand, as to intellectual concepts, it is above all to be well noted that the use of the intellect, or of the superior faculty of the soul, is two-fold. By the first use are given the very concepts both of things and relations. This is the real use. By the second use they, whencesoever given, are merely by common marks subordinated to one another, the lower to the higher, and compared among themselves according to the principle of contradiction. This is called the logical use. The logical use of the intellect is common to all the sciences; the real use is not. For a cognition given in any wise is regarded either as contained under or as opposed to a mark common to several cognitions, and this either by immediate apposition, as in judgments in order to distinct cognition, or mediately, as in reasoning, in order to adequate cognition. Thus sensuous knowledge being given, sensuous percepts are by the logical use of the intellect subordinated to other sensuous percepts, as to common concepts, and phenomena to the more general laws of phenomena. In this connection it is of the greatest moment to note that cognitions must continue to be regarded as sensuous, no matter how great may have been the logical use of the intellect upon them. For they are called sensuous on account of their origin, not of their collation by identity and opposition. Hence, empirical laws, though of the greatest generality, are, nevertheless, sensual, and the principles of sensuous form in geometry, the relations in determinate space, however much the intellect arguing according to logical rules from what is sensuously given, by pure intuition, be employed upon them, do not for that matter pass beyond the class of sense-percepts. That in sense-percepts and phenomena which precedes the logical use of the intellect is called appearance, while the reflex knowledge originating from several appearances compared by the intellect is called experience. Thus there is no way from appearance to experience except by reflection according to the logical use of the intellect. The common concepts of experience are termed empirical, its objects phenomena, and the laws as well of experience as of all sensuous cognition generally are called the laws of phenomena. Empirical concepts, then, are not by a reduction to greater universality rendered intellectual in the real sense and do not transcend the species of sensuous cognition, but, however high abstraction may carry them, remain indefinitely sensuous.

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Now as to strictly intellectual concepts in which the use of the intellect is real. Such concepts both of objects and relations are given by the very nature of the intellect, are not abstracted from any use of the senses, and do not contain any form of sensuous knowledge as such. It is needful here to take note of the extreme ambiguity of the word abstract, which, in order not to confuse our disquisition on intellectual concepts, must be removed to begin with, for properly we should say abstract from some things, not abstract something. The former denotes that in a concept we give no attention to other matters in whatsoever way they may be connected with it; but the latter, that it is not given but in the concrete and so as to be separated from what it is conjoined with. Hence an intellectual concept abstracts from everything sensuous, it is not abstracted from sensuous things, and perhaps would be more correctly called abstracting than abstract. Intellectual concepts it is more cautious, therefore, to call pure ideas, and concepts given only empirically, abstract ideas.

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From the foregoing it will be seen that it is badly to expound the sensuous to call it the more confusedly known, and the intellectual the distinctly known. For these are only logical distinctions and plainly do not touch the data underlying all logical comparison. The sensuous may be exceedingly distinct, while intellectual concepts are extremely confused. The former we observe in the prototype of sensuous knowledge, geometry; the latter, in the organon of all intellectual concepts, metaphysics. It is evident how much toil the latter is expending to dispel the fogs of confusion darkening the common intellect, though not always with the happy success of the former science. Nevertheless, any cognition retains the marks of its origin, the former, however distinct, being called by genesis sensuous; the latter, no matter how confused, remaining intellectual, as for instance, the moral concepts, which are known not experientially but by the pure intellect itself. The writer fears that Wolf by the distinction between the sensuous and the intellectual, which to him is only logical, checked, perhaps wholly, and to the great detriment of philosophy, that noble enterprise of antiquity of discussing the nature of phenomena and noumena, turning us from the investigation of these to what are frequently but logical trifles.

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The primary philosophy containing the principles of the use of pure intellect is metaphysics. But there is a science propaedeutical to it, showing the distinction of sensuous cognition from intellectual, a specimen of which we present in this dissertation. Empirical principles not being found in metaphysics, the concepts to be met with in it are not then to be sought for in the senses, but in the very nature of pure intellect; not as connate notions, but as abstracted from laws whose seat is in the mind, by attending to the actions of the mind on the occasion of experience, and hence as acquired. Of this species are possibility, existence, necessity, substance, cause, etc., with their opposites and correlates, which, never entering as parts into any sensual representation, can by no means have been abstracted thence.

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The purpose of intellectual concepts is mainly twofold; in the first place refutative, by which they are of negative use, when, shutting off sensuous concepts from noumena, though not advancing science a hair’s breadth, they maintain however its immunity from the contagion of error. In the second place dogmatic, following which the general principles of pure intellect, such as are set forth in ontology or rational psychology, go forth into an exemplar inconceivable except by pure intellect, and the common measure of all other things considered as realities, namely, noumenal perfection. The latter is such either in the theoretical or in the practical sense.[3] In the former it is the highest being, God. In the latter sense, it is moral perfection. Moral philosophy, then, inasmuch as supplying the first principles of judgment, is not cognized except by pure intellect, and itself belongs to pure philosophy, and Epicurus reducing its criteria to deduction from the sense of pleasure or pain is rightly reprehended, together with some moderns following him a certain distance from afar, as Shaftesbury and his adherents. In any class of things having variable quantity the maximum is the common measure and the principle of cognition. Now the maximum of perfection is called ideal, by Plato, Idea—for instance, his Idea of a Republic—and is the principle of all that is contained under the general notion of any perfection, inasmuch as the lesser grades are not thought determinable but by limiting the maximum. But God, the Ideal of perfection, and hence the principle of cognition, is also, as existing really, the principle of the creation of all perfection.

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To man, no intuition of intellectual concepts is given, only symbolical cognition, and intellection is granted us only by universal concepts in the abstract, not by the concrete singular. For all intuition is restricted by some principle of form under which alone anything can be discerned by the mind immediately or as singular, and not merely conceived discursively by general concepts. This formal principle of our intuition—space and time—is the condition under which something can be an object of our senses, and hence as a condition of sensuous knowledge is not a medium for intellectual intuition. Besides, all the material of our cognition is given only by the senses, but the noumenon, as such, is not conceivable by representations drawn from sensations; hence the intellectual concept, as such, is destitute of all data of human intuition. For the intuition of our mind is always passive, and therefore possible only to the extent to which something can affect our senses. But the divine intuition, the cause—not the consequence, of objects, being independent, is the archetype, and hence perfectly intellectual.

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But although phenomena are properly the appearances of things, but not ideas, or express the inner and absolute quality of objects, their cognition is nevertheless of the truest. For in the first place, being apprehended sensual concepts, they, being consequences, witness the presence of the object, contrary to Idealism; and as regards judgments concerning that which is sensuously known, since truth in judging consists in the agreement of the predicate with the given subject, and since the concept of the subject as a phenomenon is given only by relation to the sensuous cognitive faculty, the sensuously observable predicates being given according to the same, it is plain that the representations of subject and predicate are made according to common laws, and hence give occasion for perfectly true cognition.

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All sense-objects are phenomena, but that which, not touching our senses, contains the form only of sensuality, belongs to pure intuition, that is, an intuition devoid of sensations, but not on that account, intellectual. Phenomena of the external sense are examined and set forth in physics; those of the internal sense in empirical psychology. But pure human intuition is not a universal or logical concept under which, but a singular in which all sensible objects are thought, and hence contains concepts of space and time, which, since they determine nothing concerning sensible objects as to quality, are not the objects of science except as to quantity. Hence pure mathematics considers space in geometry and time in pure mechanics. To these is to be added a certain concept, intellectual to be sure in itself, but whose becoming actual in the concrete requires the auxiliary notions of time and space in the successive addition and simultaneous juxtaposition of separate units, which is the concept of number treated in arithmetic. Pure mathematics, then, expounding the form of our entire sensuous cognition, is the organon of all intuitive and distinct knowledge, and since its objects are not only the formal principles of all intuition, but themselves original intuitions, it confers cognition both perfectly true, and the model of the highest degree of clearness to others. There is given, therefore, a science of sensual things, though being phenomena there is not given a real intellection, but a logical one only; hence it is plain in what sense those borrowing from the Eleatic school are to be thought to have denied a science of phenomena.



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The principle of the form of a universe is that which contains the cause of the universal tie by means of which all substances and their states pertain to one which is called a world. The principle of the form of the sensible world is that which contains the cause of the universal tie of all things regarded as phenomena. The form of the intelligible world acknowledges an objective principle, that is, some cause by which it is the colligation of what exists in it. But the world regarded as phenomenon, that is, in respect to the sensibility of the human mind, acknowledges no principle of form but a subjective one, that is, a certain mental law by which it is necessary that all things qualified for being objects of the senses would seem to pertain necessarily to the same whole. Whatever be, therefore, the principle of the form of the sensible world, it will comprise only actual things in as far as thought of as possibly falling under sense-perception; hence neither immaterial substances, which as such are excluded by definition from the external senses altogether, nor the cause of the world, which, since by it the mind exists and has the power of sense-perception, cannot be the object of the senses. These formal principles of the phenomenal universe which are absolutely primary, universal, and, so to speak, the outlines and conditions of anything else whatsoever in human sensuous cognition, I shall now show to be two: time and space.

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OF TIME[edit]

1. The idea of time does not originate in, but is presupposed by the senses. Whether things falling under sense-perception be simultaneous or in line of succession cannot be represented but by the idea of time; nor does succession beget the concept of time; it appeals to it. Hence the notion of time, though acquired by experience, is badly defined by a series of actual things existing one after another, for what the word after means I understand only by the previous concept of time. For those things are after one another which exist at different times, as those are simultaneous which exist at the same time.

2. The idea of time is singular, not general. For any time whatever is thought only as a part of one and the same unmeasured time. If you think two years you cannot represent them to yourself but in a mutually determinate position, and if they do not immediately follow one the other, you cannot think of them except as connected by some intermediate time. Which of different times is first and which later can be defined in no way by any marks conceivable by the intellect, unless you are willing to run into a circle, and the mind discerns it by no more than one intuition. Besides, we conceive of all actual things as posited in time, not as contained as common marks under a general notion of time.

3. The idea of time, therefore, is an intuition, and being conceived before all sensation as the condition of the relations occurring in sensible things, it is not a sensual but pure intuition.

4. Time is a continuous quantity and the principle of the laws of continuity in the changes of the universe. For a continuous quantity is one which does not consist of simple parts. But since by time are only thought relations without any mutually related data, there is in time—as a quantity—composition, which being conceived wholly removed leaves nothing over. But a composite of which, composition being removed, nothing is left, does not consist of simple parts. Therefore, etc. Any part of time, then, is time; and the simple things in time, namely, the moments, are not parts of it, but termini between which time intervenes. For two moments being given, time is not given, except as in them actualities succeed each other; hence, beside the given moment it is necessary that time be given in the latter part of which there is another moment.

The metaphysical law of continuity is this: All changes are continuous or flowing, that is, opposite states succeed each other only by an intermediate series of different states. For since two opposite states are in different moments of time, and some time is always intercepted between two moments, in which infinite series of moments the substance is neither in one assignable state nor the other, nor yet in none, it will be in different states, and so on infinitely.

The celebrated Kästner, calling in question this Leibnitzian law,[4] calls on its defenders to demonstrate that the continuous motion of a point around the sides of a triangle is impossible, it being necessary to prove this if the law of continuity be granted. Here is the demonstration required. Let the letters a b c denote the three angular points of a rectilineal triangle. If the point did move continuously over the lines ab, bc, ca, that is, over the perimeter of the figure, it would be necessary for it to move at the point b in the direction ab, and also at the same point b in the direction bc. These motions being diverse, they cannot be simultaneous. Therefore, the moment of presence of the movable point at vertex b, considered as moving in the direction ab, is different from the moment of presence of the movable point at the same vertex b, considered as moving in the same direction bc. But between two moments there is time; therefore, the movable point is present at point b for some time, that is, it rests. Therefore it does not move continuously, which is contrary to the assumption. The same demonstration is valid for motion over any right lines including an assignable angle. Hence a body does not change its direction in continuous motion except by following a line no part of which is straight, that is, a curve, as Leibnitz maintained.

5. Time is not something objective and real, neither a substance, nor an accident, nor a relation. It is the subjective condition necessary by the nature of the human mind for coordinating any sensible objects among themselves by a certain law; time is a pure intuition. Substances as well as accidents we co-ordinate whether according to simultaneity or succession by the concept only of time; hence the notion of time as the principle of form outranks the concepts of the former. Any relations so far as occurring in sense-perception, whether simultaneous or successive, involve nothing but the determination of positions in time, to wit, either in the same point or in different points of the latter.

Those who assert the objective reality of time either conceive of it as a continuous flow in what exists, without, however, any existing thing, as is done especially by the English philosophers, an absurd fiction, or as something real abstracted from the succession of inner states, as it has been put by Leibnitz and his followers. The falsity of the latter opinion, besides obviously exposing it to the vicious circle in the definition of time, and, moreover, plainly neglecting simultaneity, the most important consequence of time, disturbs all sound reason, because it demands instead of the determining of the laws of motion by the measure of time, that time itself, as to its nature, be determined by what is observed in motion or some series of inner changes, whereby plainly all certitude of rules is abolished. That we can estimate the quantity of time only in the concrete, namely, either by motion or by a series of thoughts, arises from the concept of time resting only on an inherent mental law, it not being a connate intuition; whence the act of the mind co-ordinating the impressions is elicited only by the aid of the senses. So far from its being possible to deduce and explain the concept of time from some other source by force of reason, it is presupposed by the very principle of contradiction, it underlies it by way of condition. For a and not-a are not repugnant unless thought of the same thing simultaneously, that is, at the same time; they may belong to the same thing after each other, at different times. Hence the possibility of changes is not thinkable except in time. Time is not thinkable by changes, but reversely.[5]

6. But although time posited in itself and absolutely be an imaginary thing, yet as appertaining to the immutable law of sensible things as such, it is a perfectly true concept, and the patent condition of intuitive representation throughout all the infinite range of possible sense-objects. For since simultaneous things as such cannot be placed before the senses but by the aid of time, and since changes are unthinkable except by time, it is obvious that this concept contains the universal form of phenomena, and that, indeed, all events observable in the world, all motions, all internal changes, agree necessarily with the temporal axioms of cognition which we have partly expounded, since only under these conditions can they become sense-objects and be co-ordinated. It is, therefore, absurd to excite reason against the primary postulates of pure time, as, for example, continuity, etc., since they follow from laws prior and superior to which nothing is found, and since reason herself in the use of the principle of contradiction cannot dispense with the support of this concept, so primitive and original is it.

7. Time, then, is the absolutely first formal principle of the sensible world. For all sensible things of whatsoever description are unthinkable except as posited either simultaneously or one after another, and, indeed, as if involved and mutually related by determinate position in the tract of unique time, so that by this primary concept of everything sensuous originates necessarily that formal whole which is not a part of another, that is, the phenomenal World.

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OF SPACE[edit]

A. The concept of space is not abstracted from external sensations. For I am unable to conceive of anything posited without me unless by representing it as in a place different from that in which I am, and of things as mutually outside of each other unless by locating them in different places in space. Therefore the possibility of external perceptions, as such, presupposes and does not create the concept of space, so that, although what is in space affects the senses, space cannot itself be derived from the senses.

B. The concept of space is a singular representation comprehending all things in itself, not an abstract and common notion containing them under itself. What are called several spaces are only parts of the same immense space mutually related by certain positions, nor can you conceive of a cubic foot except as being bounded in all directions by surrounding space.

C. The concept of space, therefore, is a pure intuition, being a singular concept, not made up by sensations, but itself the fundamental form of all external sensation. This pure intuition is in fact easily perceived in geometrical axioms, and any mental construction of postulates or even problems. That in space there are no more than three dimensions, that between two points there is but one straight line, that in a plane surface from a given point with a given right line a circle is describable, are not conclusions from some universal notion of space, but only discernible in space as in the concrete. Which things in a given space lie toward one side and which are turned toward the other can by no acuteness of reasoning be described discursively or reduced to intellectual marks. There being in perfectly similar and equal but incongruous solids, such as the right and the left hand, conceived of solely as to extent, or spherical triangles in opposite hemispheres, a difference rendering impossible the coincidence of their limits of extension, although for all that can be stated in marks intelligible to the mind by speech they are interchangeable, it is patent that only by pure intuition can the difference, namely, incongruity, be noticed. Geometry, therefore, uses principles not only undoubted and discursive but falling under the mental view, and the obviousness of its demonstrations—which means the clearness of certain cognition in as far as assimilated to sensual knowledge—is not only greatest, but the only one which is given in the pure sciences, and the exemplar and medium of all obviousness in the others. For, since geometry considers the relations of space, the concept of which contains the very form of all sensual intuition, nothing that is perceived by the external sense can be clear and perspicuous unless by means of that intuition which it is the business of geometry to contemplate. Besides, this science does not demonstrate its universal propositions by thinking the object through the universal concept, as is done in intellectual disquisition, but by submitting it to the eyes in a single intuition, as is done in matters of sense.[6]

D. Space is not something objective and real, neither substance, nor accident, nor relation; but subjective and ideal, arising by fixed law from the nature of the mind like an outline for the mutual co-ordination of all external sensations whatsoever. Those who defend the reality of space either conceive of it as an absolute and immense receptacle of possible things, an opinion which, besides the English, pleases most geometricians, or they contend for its being the relation of existing things itself, which clearly vanishes in the removal of things and is thinkable only in actual things, as besides Leibnitz, is maintained by most of our countrymen. The first inane fiction of the reason, imagining true infinite relation without any mutually related things, pertains to the world of fable. But the adherents of the second opinion fall into a much worse error. Whilst the former only cast an obstacle in the way of some rational or noumenal concepts, otherwise most recondite, such as questions concerning the spiritual world, omnipresence, etc., the latter place themselves in fiat opposition to the very phenomena, and to the most faithful interpreter of all phenomena, to geometry. For, not to enlarge upon the obvious circle in which they become involved in defining space, they cast forth geometry, thrown down from the pinnacle of certitude, into the number of those sciences whose principles are empirical. If we have obtained all the properties of space by experience from external relations only, geometrical axioms have only comparative universality, such as is acquired by induction. They have universality evident as far as observed, but neither necessity, except as far as the laws of nature may be established, nor precision, except what is arbitrarily made. There is hope, as in empirical sciences, that a space may some time be discovered endowed with other primary properties, perchance even a rectilinear figure of two lines.

E. Though the concept of space as an objective and real thing or quality is imaginary, it is nevertheless in respect to all sensible things not only perfectly true, it is the foundation of truth in external sensibility. Things cannot appear to the senses under any form but by means of a power of the soul co-ordinating all sensations in accordance with a fixed law implanted in its nature. Since, therefore, nothing at all can be given the senses except conformably to the primary axioms of space and their consequences which are taught by geometry, though their principle be but subjective, yet the soul will necessarily agree with them, since to this extent it agrees with itself; and the laws of sensuality will be the laws of nature so far as it can be perceived by our senses. Nature, therefore, is subject with absolute precision to all the precepts of geometry as to all the properties of space there demonstrated, this being the subjective condition, not hypothetically but intuitively given, of every phenomenon in which nature can ever be revealed to the senses. Surely, unless the concept of space were originally given by the nature of the mind, so as to cause him to toil in vain who should labor to fashion mentally any relations other than those prescribed by it, since in the fiction he would be compelled to employ the aid of this very same concept, geometry could not be used very safely in natural philosophy, For it might be doubted whether this same notion drawn from experience would agree sufficiently with nature, the determinations from which it was abstracted being, perchance, denied, a suspicion of which has entered some minds already. Space, then, is the absolutely first formal principle of the sensible world, not only because by its concept the objects of the universe can be phenomena, but especially for the reason that it is. essentially but one, comprising all externally sensible things whatsoever; and hence constitutes the principle of the universe, that is, of that whole which cannot be the part of another.


Here, then, are two principles of sensuous cognition, not, as in intellectual knowledge, general concepts, but single and nevertheless pure intuition, in which the parts, and especially the simple parts, do not, as the laws of reason prescribe, contain the possibility of the composite, but, according to the pattern of sensuous intuition, the infinite contains the reason of the part, and finally of its thinkable simple part or rather limit. For unless infinite space as well as infinite time be given, no definite space and time is assignable by limitation, and a point as well as a moment is unthinkable by itself and only conceived in a space and time already given as the limits. All primitive properties of these concepts are then beyond the purview of reason, and hence cannot intellectually be explained in any way. Nevertheless, they are what underlies the intellect when from intuitive primary data it derives consequences according to logical laws with the greatest possible certainty. One of these concepts properly concerns the intuition of the object; the other the state, especially the representative state. Hence space is employed as the type even of the concept of time itself, representing it by a line, and its limits—moments—by points. Time, on the other hand, approaches more to a universal and rational concept, comprising under its relations all things whatsoever, to wit, space itself, and besides, those accidents which are not comprehended in the relations of space, such as the thoughts of the soul. Again, time, besides this, though it certainly does not dictate the laws of reason, yet constitutes the principal conditions under favor of which the mind compares its notions according to the laws of reason. Thus, I cannot judge what is impossible except by predicating a and not-a of the same subject at the same time. And especially, considering experience, though the reference of cause to effect in external objects were to lack the relations of space, still in all things, external or internal, the mind could by the auxiliary relation of time alone be informed which is the first and which latter or caused. And even the quantity of space itself cannot be rendered intelligible unless, referring it to measure as to a unity, we set it forth in number, which itself is but multiplicity distinctly cognized by numeration, that is, by the successive addition of one to one in a given time.

Lastly, the question will arise in any one as if spontaneously, whether either concept be connate or acquired. The latter by what has been shown seems refuted already, but the former, smoothing the way for lazy philosophy, declaring vain by the citing of a first cause any further quest, is not to be admitted thus rashly. But beyond doubt either concept is acquired, not, it is true, abstracted from the sense of objects, for sensation gives the matter not the form of human cognition, but from the very action of the mind co-ordinating its sense-percepts in accordance with perpetual laws, as though an immutable type, and hence to be known intuitively. For sensations excite this act of the mind but do not influence intuition, neither is there anything connate here except the law of the soul in accordance with which it conjoins in a certain way its sensations derived from the presence of an object.



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Those who deem space and time to be something real and the absolute bond, so to speak, of all possible substances in space, hold nothing else to be required in order to conceive how an original relation can belong to several existing things as the primitive condition of possible influence and the principle of the essential form of the universe. For since whatever exists is, according to their opinion, necessarily somewhere, it seems to them quite superfluous to inquire why things are present to one another in a certain manner, since this is of itself determined by the universality of all-comprehending space. But this concept, besides relating as has been shown rather to the sensuous laws of the subject than to the conditions of the objects themselves, even granting it the greatest reality, still denotes nothing but the intuitively given possibility of universal co-ordination, leaving undealt with the question solvable only by the intellect: In what principle does this very relation of all substances rest, which intuitively regarded is called space? The question of the principle of the form of the intelligible world turns, therefore, upon making apparent in what manner it is possible for several substances to be in mutual commerce, and for this reason to pertain to the same whole, which is called world. We do not here consider the world, let it be understood, as to matter, that is, as to the nature of the substances of which it consists, whether they be material or immaterial, but as to form, that is to say, how among several things taken separately a connection, and among them all, totality can have place.

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Several substances being given, the principle of their possible intercommunication is not apparent from their existence solely, but something else is required besides from which their mutual relations may be understood. For on account of mere existence they are not necessarily related to anything, unless it be to their cause; but the relation of an effect to the cause is not intercommunication, but dependence. Therefore, if any commerce intervenes among them, there is need of an exactly determining specific reason.

The sham cause in physical influence consists in rashly assuming that the commerce of substance and transitive forces is sufficiently knowable from their mere existence. Hence it is not so much a system as rather the neglect of all philosophical system as a superfluity in the argument. Freeing the concept from this defect, we shall have a species of commerce alone deserving to be called real, and from which the whole constituting the world merits being called real, and not ideal or imaginary.

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A whole from necessary substances is impossible. For, since the existence of each stands for itself without dependence on any other, a dependence which in necessary substances clearly cannot befall, it is plain that not only does the intercommunication of substances (that is, the reciprocal dependence of their states) not follow from their existence, but as necessary substances cannot belong to them at all.

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The whole, therefore, of substances is a whole of contingent things, and the world consists essentially of only contingent things. Besides, no necessary substance is in connection with the world except as a cause with the effect, and, therefore, not as a part with its complements making up a whole, since the bond connecting parts is mutual dependence, which in a necessary being cannot occur. The cause, therefore, of the world is an extramundane being, and so is not the soul of the world, nor is its presence in the world local, but virtual.

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The mundane substances are beings from, another being; not from several, but all from one. For, suppose them to be caused by several necessary beings. In intercommunication there are not effects from causes alien to all mutual relation. Hence, the unity in the conjunction of the substances of the universe is the consequence of the dependence of all on one. Therefore, the form of the universe witnesses the cause of matter, and only the sole cause of all things is the cause of the universe, nor is there an architect of the world not at the same time its creator.

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If there were several primary and necessary causes together with their effects, their works would be worlds, not a world, since they would in no wise be connected into one whole. And vice versa, if there be several actual worlds without one another, several primary and necessary causes are given, so, however, as to give intercommunication neither to one world with another, nor to the cause of one with the world caused by another.

Several actual worlds without one another are not, therefore, impossible by the very concept, as Wolf hastily concluded from the notion of a complex or multiplicity which he deemed sufficient to a whole, as such, but only on condition that there exist but one necessary cause of all things. If several are admitted, several worlds without one another will be possible in the strictest metaphysical sense.

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If, as we validly conclude from a given world to a single cause of all its parts, we may similarly argue reversely from the given cause common to all to their interconnection, and hence to the form of the world—though I confess this conclusion does not seem as plain to me—then the primary connection of substances will not be contingent but by the sustentation of all by the common principle, necessary, and hence the harmony proceeding from their very subsistence founded in a common cause would proceed according to the usual rules. Such a harmony I term established generally; as that which does not take place except as far as any individual states of a substance are adapted to the condition of another is harmony established particularly; the communion by the former being real and physical, by the latter ideal and sympathetic. All communion, then, of the substance of the universe is eternally established by the common cause of all, and either established generally by physical influence—as amended; see paragraph 17—or adapted particularly to their states; and the latter either rests originally in the primary constitution of every substance or is impressed on the occasion of any change whatever; the first being called pre-established harmony, the latter occasionalism. If, then, on account of the sustentation of all substances by one, the conjunction of all constituting them a unit be necessary, the universal commerce of substances will be by physical influence, and the world a real whole; if not, the commerce will be sympathetic, that is a harmony without true commerce, and the world only an ideal whole. To me the former, though not demonstrated, appears abundantly proved by other reasons.


If it were right to overstep a little the limits of apodictic certainty befitting metaphysics, it would seem worth while to trace out some things pertaining not merely to the laws but even to the causes of sensuous intuition, which are only intellectually knowable. Of course the human mind is not affected by external things, and the world does not lie open to its insight infinitely, except as far as itself together with all other things is sustained by the same infinite power of one. Hence it does not perceive external things but by the presence of the same common sustaining cause; and hence space, which is the universal and necessary condition of the joint presence of everything known sensuously, may be called the phenomenal omnipresence, for the cause of the universe is not present to all things and everything, as being in their places, but their places, that is the relations of the substances, are possible, because it is intimately present to all. Furthermore, since the possibility of the changes and successions of all things whose principle as far as sensuously known resides in the concept of time, supposes the continuous existence of the subject whose opposite states succeed; that whose states are in flux, lasting not, however, unless sustained by another; the concept of time as one infinite and immutable in which all things are and last, is the phenomenal eternity of the general cause.[7] But it seems more cautious to hug the shore of the cognitions granted to us by the mediocrity of our intellect than to be carried out upon the high seas of such mystic investigations, like Malebranche, whose opinion that we see all things in God is pretty nearly what has here been expounded.



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In all sciences whose principles are given intuitively, whether by sensual intuition, that is, experience, or by an intuition sensuous, to be sure, but pure—the concepts of space, time, and number—that is to say, in the natural and in the mathematical sciences, use gives method, and by trying and finding after the science has been carried to some degree of copiousness and consonancy it appears by what method and in what direction we must proceed in order to finish and to purify it by removing the defects of error as well as of confused thoughts; exactly as grammar after the more copious use of speech, and style after the appearance of choice examples in poetry and oratory, furnished vantage-ground to rules and to discipline. But the use of the intellect in the sciences whose primitive concepts as well as axioms are given by sensuous intuition is only logical, that is, by it we only subordinate cognitions to one another according to their relative universality conformably to the principle of contradiction, phenomena to more general phenomena, and consequences of pure intuition to intuitive axioms. But in pure philosophy, such as metaphysics, in which the use of the intellect in respect to principles is real, that is to say, where the primary concept of things and relations and the very axioms are given originally by the pure intellect itself, and not being intuitions do not enjoy immunity from error, the method precedes the whole science, and whatever is attempted before its precepts are thoroughly discussed and firmly established is looked upon as rashly conceived and to be rejected among vain instances of mental playfulness. For, since here the right use of the reason constitutes the very principles and the objects as well, what axioms are to be thought of concerning them become primarily known solely by its own nature, the exposition of the laws of pure reason is the very origin of the science, and their distinction from spurious laws the criterion of truth. The method of the science not being practiced much nowadays, except what logic prescribes to all sciences generally, that fitted for the peculiar nature of metaphysics being simply ignored, it is no wonder that those who everlastingly turn the Sisyphean stone of this inquiry do not seem so far to have made much progress. Though here I neither can nor will expatiate upon so important and extensive a subject, I shall briefly shadow forth what constitutes no despicable part of this method, namely, the infection between sensuous and intellectual cognition, not only as creeping in on those incautious in the application of principles, but even producing spurious principles under the appearance of axioms.

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In substance the whole method of metaphysics as to the sensuous and the intellectual amounts to this precept; to take care not to allow the principles at home in sensuous cognition to outstray their limits and affect the intellectual concepts. For, since the predicate in any judgment enounced intellectually is a condition in the absence of which the subject is asserted to be unthinkable, the predicate hence being the principle of cognition, it will, if a sensuous concept, be only the condition of a possible sensuous cognition—and hence will square well enough with the subject of a judgment whose concept is also sensuous. But if it be applied to an intellectual concept, the judgment will be valid only according to subjective laws, and hence must not be affirmed objectively and predicated of the intellectual notion itself, but only as a condition in the absence of which the sensuous cognition of the given concept does not take place.[8]

Now, since the tricks of the intellect by the subordination of sensuous concepts as though intellectual marks may be called, analogously to the accepted meaning, a fallacy of subreption, the exchanging of intellectual and sensual concepts will be a metaphysical fallacy of subreption, the intellectualized phenomenon, if the barbarous expression be permissible, and hence I call such a hybrid axiom as palms off the sensuous as necessarily adhering to the intellectual concept, a surreptitious axiom. From these spurious axioms have gone forth, and are rife throughout metaphysics, principles deceiving the intellect. In order that we may have, however, a readily and clearly knowable criterion of those judgments, a touchstone, so to speak, by which to distinguish them from genuine judgments, and at the same time if, perhaps, they seem to cling tenaciously to the intellect, an assaying art by which we can justly estimate how much belongs to the sensuous and how much to the intellectual sphere, I think it necessary to go into the question more deeply.

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Here, then, is the principle of reduction for any spurious axiom: If concerning any intellectual concept something pertaining to time and space relations be predicated generally, it is not to be enounced objectively, but denotes only the condition without which the given concept is not knowable sensuously. That such an axiom is spurious, and, if not false, at least a rash and question-begging assertion, appears thus: the subject of the judgment being intellectually conceived pertains to the object, whilst the predicate, since it contains the determinations of space and time, pertains only to the conditions of human sensuous cognition, which, not adhering of necessity to any cognition whatsoever of the object, cannot be enounced concerning the given intellectual concept universally. The intellect’s being so readily subject to this fallacy of subreption comes of its being deceived under the plea of another and perfectly true rule. For we rightly suppose that that which can be cognized by no intuition whatever is utterly unthinkable and hence impossible. But since we cannot attain by any mental striving, even fictitiously, to any other intuition but that according to the form of space and time, it happens that we deem all intuition whatever impossible which is not bound by these laws, passing by the pure intellectual intuition exempt from the laws of the senses, such as the divine, by Plato called the Idea, and hence subject all possible given things to the sensual axioms of space and time.

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All sleights of substitution of sensuous cognition under guise of intellectual concepts, from which spurious axioms originate, can be reduced to three species, whose general formulae are the following:

1. The sensual condition under which alone the intuition of an object is possible, is the condition of its possibility.

2. The sensual condition under which alone data can be compared in order to form the intellectual concept of the object, is the condition of the very possibility of the object.

3. The sensual condition under which alone the subsumption of an object under a given intellectual concept is possible, is the condition of the possibility of the object.

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A spurious axiom of the first class is: Whatever is, is somewhere and sometime.[9] Now by this spurious principle all beings, even though they be intellectually cognized, are restricted in existence by the conditions of space and time. Hence people discuss all sorts of inane questions, such as concerning the places of immaterial substances—of which, for that very reason, there is no sensuous intuition, nor, under that form, any representation—in the corporeal universe, or the seat of the soul; and as they improperly mix sensual things with intellectual concepts, like square figures with round, it oftens happens that of the disputants one appears as milking a he-goat, and the other as holding the sieve under. The presence of immaterial substances in the corporeal world is virtual, not local, though thus improperly talked about. Space does not contain the conditions of possible mutual activities, except those of matter. What may constitute the external relations of forces in immaterial substances, as well among themselves as toward bodies, altogether escapes the human intellect, as was acutely noted, for instance, in a letter to a German prince by the clear-sighted Euler, otherwise a great investigator and judge of phenomena. But when people have arrived at the concept of a highest and extra-mundane being, they are fooled by these shadows flitting before the intellect to a degree beyond the force of language to express. The presence of God they figure to themselves as a local one, involving God in the world as if also comprised in infinite space, compensating Him for this limitation by a locality, so to speak, eminently conceived, that is, infinite. But it is absolutely impossible to be at the same time in several places, since different places are mutually without each other, and hence what is in several places is outside of itself, which implies being present to itself externally. But as to time, having not only exempted it from the laws of sensual knowledge, but transferred it beyond the limits of the world to the extra-mundane Being Himself as a condition of His existence, they involve themselves in an inextricable labyrinth. Hence they cudgel their brains with absurd questions, such as, for instance, why God did not make the world many centuries earlier. They persuade themselves that it is easy to conceive, to be sure, how God may discern what is present, that is, what is actual in the time in which he is, but how He may foresee what is future, that is, what is actual in the time in which He is not yet, they deem an intellectual difficulty; as if the existence of the Necessary Being descended through all the moments of an imaginary time, and, having already exhausted a part of His duration, saw before Him the eternity He was yet to live simultaneously with the present events of the world. All these difficulties upon proper insight into the notion of time vanish like smoke.

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The prejudices of the second species, since they impose upon the intellect by the sensual conditions restricting the mind if it wishes in certain cases to attain to what is intellectual, lurk more deeply. One of them is that which affects knowledge of quantity, the other that affecting knowledge of qualities generally. The former is: every actual multiplicity can be given numerically, and hence, every infinite quantity; the latter, whatever is impossible contradicts itself. In either of them the concept of time, it is true, does not enter into the very notion of the predicate, nor is it attributed as a qualification to the subject. But yet it serves as a means for forming an idea of the predicate, and thus, being a condition, affects the intellectual concept of the subject to the extent that the latter is only attained by its aid.

As to the first, as every quantity and any series whatever are distinctly known only by successive co-ordination, the intellectual concept of amount and multiplicity arises only by the aid of this concept of time, and never attains to completeness unless the synthesis can be gone through with in finite time. It is hence that the infinite series of co-ordinate things cannot be comprehended distinctly according to the limits of our intellect; it hence by the fallacy of subreption seems impossible. According to the laws of pure intellect any series of effects has its principle, that is, there is not given in a series of effects a regress without a limit; whilst according to sensual laws any series of co-ordinate things has its assignable beginning. These propositions, the latter of which involves the mensurability of the series, the former the dependence of the whole, are taken hastily for identical. In the same way, to the argument of the intellect, proving that a substantial composite being given so are the elements of composition, that is, the simple things, there is adjoined a supposititious one suborned from sensual knowledge, namely, that in such a composite there is not given an infinite regress in the composition of the parts, that is to say, that in any composite there is given a definite number of parts, a sense certainly not germane to the former, and hence substituted rashly for it. For that the quantity of the world is limited, not the maximum, that it owns a principle, that bodies consist of simple parts, can certainly be cognized rationally. But that the universe as to its mass is mathematically finite, that its age as elapsed can be given by measure, that the number of simple parts constituting any body whatever is a definite number, are propositions openly proclaiming their origin from the nature of sensual knowledge; however true they may be held to be, they bear the undoubted stigma of their origin.

As for the latter spurious axiom, it originates from a rash conversion of the principle of contradiction. For to this primitive judgment the concept of time adheres to the extent that contradictorily opposed data being given at the same time in the same thing, the impossibility is plain, which is enounced thus: whatever simultaneously is and is not, is impossible. Here, as the intellect predicates something in a case given according to sensual laws, the judgment is perfectly true and obvious. On the contrary, converting this axiom, saying: whatever is impossible is and is not at the same time, or involves a contradiction, we predicate through sensual knowledge something concerning the object of reason generally, thus subjecting the intellectual conception of the possible and the impossible to the conditions of sensual knowledge, namely, to the relations of time; which certainly is true enough of the laws restricting and limiting the human intellect, but cannot be conceded objectively and generally by any means. Of course, our intellect perceives no impossibility except where it can note the simultaneous enunciation of opposites concerning the same thing, that is, only where contradiction occurs. Wherever, therefore, this contradiction does not occur, there is no room for the judgment of impossibility by the human intellect. But that on this account it should be open to no intellect whatever, and hence that what does not involve contradiction is therefore possible, is concluded rashly by taking the subjective conditions of judgment for objective ones. It is for this reason that a host of fictitious forces, gotten up ad libitum, bursts, in the absence of self-contradiction, from any constructive, or, if you prefer, from every chimerical mind. For as a force is nothing but a relation of a substance a to something else b, an accident, as of a reason to the consequence, the possibility of any force does not rest in the identity of the cause and the effect, or the substance and the accident, and hence even the impossibility of forces made up falsely does not depend solely on contradiction. Therefore it is not permissible to assume as possible any original force unless the force be given by experience. Neither can the possibility be conceived a priori by any perspicacity of the intellect.

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The spurious axioms of the third kind from conditions proper to the subject whence they are transferred rashly to the object are plentiful, not, as in those of the Second Class, because the only way to the intellectual concept lies through the sensuous data, but because only by aid of the latter can the concept be applied to that which is given by experience, that is, can we know whether something is contained under a certain intellectual concept or not. To this class belongs the threadbare one of the schools: whatever exists contingently does at some time not exist. This spurious principle springs from the poverty of the intellect, having insight frequently into the nominal, rarely into the real, marks of contingency or necessity. Hence, whether the opposite of any substance be possible, an insight hardly obtained from a priori marks, is not otherwise known than by its being evident that at some time that substance was not; and changes rather witness contingency than contingency mutability, so that were nothing fleeting and transitory to occur in the world, a notion of contingence would hardly be possible in us. Therefore, though the direct proposition is perfectly true: whatever at some time was not is contingent, its converse indicates nothing but the conditions under which we can alone distinguish whether something exists necessarily or contingently. Hence if enunciated as a subjective law, which indeed it is, it should be enounced thus: Sufficient marks of contingency of that of which it is not evident that at some time it was not, are not, by common intelligence, given. This, however, tacitly deviates into an objective condition, as though in its absence there were no room for contingence; which being done, a counterfeit and erroneous axiom arises. For this world though existing contingently is sempiternal, that is, simultaneous with all time. It is a rash assertion that there was a time when it did not exist.

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To these spurious principles must be added some others of great affinity with them, not imparting to the given intellectual concept any blemish of sensuous cognition, but deceiving the intellect so as to take them for arguments drawn from the object, though they are commended to us only by the peculiar nature. of the intellect for the convenience of its free and ample use. Therefore, these as well as those enumerated above, rest in subjective reasons, although not in the laws of sensuous, but in those of intellectual cognition itself, namely, in the conditions under which it appears easy and quick to the mind to make use of its insight. I shall beg leave to throw in here, by way of conclusion, some mention of these principles, not as yet, as far as I know, set forth distinctly. I call, then, principles of convenience rules of judging to which we freely submit, and to which we adhere as if they were axioms, for the only reason that, were we to depart from them, scarcely any judgment concerning a given object would be permissible to our intellect. In this list belong the following: First, that by which we assume that everything in the universe is done according to the order of nature

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