Introduction to Immanuel Kant

Immanuel Kant was born in 1724 in the Prussian city of Konigsberg, where he lived until his death in 1804. His work is divided into two basic periods: the precritical years of 1747 to 1770, and the critical years of 1770 to his death in 1804. In his precritical period he was a rationalist in the tradition of Gottfried Leibniz, the great 17th century philosopher whose students dominated the Prussian philosophical scene of Kant's school years. In order to understand Kant, we'll first have to take a quick look at Leibniz and his followers.

Leibniz was committed to the idea that the world of phenomena, or the world of everyday experience, is in some sense ideal or dependent on the human mind, and therefore not fully real. Rather, what is fundamentally real is the world of what Leibniz calls metaphysical reality, which consists of things called monads. Monads are simple immaterial substances with varying degrees of consciousness, each of which contains all of its determinations within itself. That is to say, it contains the power to determine its entire "life history" without interacting with any other monad. Indeed, monads never do interact with each other, and the apparent interaction that a monad such as a human subject experiences in the world of appearances is just a phenomenon resulting from its own self-determination in the world of metaphysical reality.

Because space and time are relational properties—that is, they involve relations between objects, such as “prior to,” “later than,” “to the left of,” etc.—they too are merely ideal abstractions from the nonrelational properties of monads. This can be called a kind of material idealism, because the “matter” of everything that exists is in fact mental or ideal. Metaphysical reality consists of mental substances, and phenomenal reality consists of mental abstractions from their determinations.

Due to the limitations of our cognitive capacities, we humans can merely grasp indistinctly at knowledge of metaphysical reality. Only god can know that world fully as it is in itself. However, we do have innate ideas, or concepts which we possess prior to any experience and which enable us to know things a priori, that is, independently of experience. In particular, Leibniz believes we can know the truths of mathematics, geometry, logic, metaphysics, morality, and theology a priori. By means of innate ideas and conceptual analysis—that is, breaking concepts down into their constituent parts—we can increase the clarity and distinctness of our knowledge, though we can never have absolutely clear and distinct knowledge like god.

In his precritical period Kant's philosophy was structurally Leibnizian, in the sense that it was based on Leibniz' basic conception of the distinction between metaphysical reality and the world of appearances. Already in this period Kant rejected various substantive Leibnizian principles, most notably the principle of metaphysical noninteraction, but we don't need to go into that for our purposes. In the 1760s, however, Kant read the work of David Hume, one of the greatest philosophers of the Scottish Enlightenment, and the seeds were planted in his mind for a radical break with the Leibnizian tradition.

Hume had attacked the kind of a priori knowledge which Leibniz claimed to have established, arguing that we can only have a priori knowledge of what he called "relations of ideas," never of "matters of fact." These categories correspond to what Kant would call analytic and synthetic judgements. Analytic judgements, or relations of ideas, have truth values that depend solely on the meanings of the terms involved. For instance, the judgement "all bachelors are unmarried men" is analytic, because "unmarried man" is just the definition of bachelor. Synthetic judgements, on the other hand, or matters of fact, have truth values that depend on more than just the meanings of the terms involved. For instance, the judgement "it is raining today" is synthetic, because nothing in the definition of "today" implies that it is raining, or vice versa.

Hume's argument was that there can be no synthetic a priori knowledge of any sort. Rather, all a priori propositions must be analytic, and all synthetic propositions must be a posteriori. Hume's rejection of synthetic a priori knowledge was based on his empiricism, that is, his belief that all of our ideas are derived from experience. For Hume, there is nothing comparable to Leibniz' innate ideas which could give us a priori cognition of matters of fact. Without such a faculty we have no way of knowing substantive truths about the world independently of experience. As a result, Hume concluded that all philosophical truths are merely a posteriori and justified, if at all, on the basis of psychological habit.

Kant saw this conclusion as a threat to the very possibility of philosophy. If philosophical cognitions were based on mere habit, Kant believed, they would lose their normativity and necessity. That is, we would have no reason to believe that they were true at all, much less that they were true in all possible worlds, which Kant considered an essential feature of philosophical truths. We might as a matter of psychological fact be unable to cease believing them, but that is no substitute for the traditional aim of philosophy, that is, to investigate what we ought to believe rather than just what we do believe.

Kant had been gradually moving away from his Leibnizian heritage since the beginning of his career, but his reading of Hume brought him to the conclusion that a radical break was needed with what he would come to call the dogmatism of the rationalists. This didn't mean that the rationalist heritage was to be rejected entirely, but it did mean that it would have to be critically reassessed and placed within strict boundaries to prevent the excessive and unjustifiable claims that had rendered it vulnerable to Hume's critique.

This was the project that Kant undertook in his Critique of Pure Reason, first published in 1781 after a decade of near-total philosophical silence (his so-called "silent decade"). As Kant described it, his fundamental project in the Critique of Pure Reason, also known as the first Critique, was to explain the possibility of synthetic a priori judgements. In order to do this, he needed to introduce a fundamentally new perspective or metaphilosophy, which he called transcendental idealism.

Transcendental idealism is to be contrasted with Leibnizian or material idealism, which as we saw is the doctrine that the matter or stuff of appearances is an ideal or quasi-illusory abstraction from fundamental metaphysical reality. Rather than being a material idealism, transcendental idealism is a kind of formal idealism, meaning that what is ideal is not the matter of experience but only its form, that is to say its spatiotemporal and conceptual characteristics. To understand what this means, it will help to look at the other word in the term, namely, "transcendental."

Transcendental is a term of art that Kant uses to characterize his fundamental subject of inquiry in the Critique: the investigation of how a priori knowledge of objects is possible. His fundamental move in this regard was to introduce a conception of knowledge that marked a radical break with all philosophers who had come before him, both rationalist and empiricist. This radical break consisted in arguing that the objects of our knowledge are not things in themselves, but only phenomena, or things as they appear to us. This may sound like Leibniz' idealism after all, but there are several features of Kant's theory which make it fundamentally different. The most important difference concerns the possibility of knowledge of things in themselves. For Leibniz, as you'll recall, we can attain some knowledge of things in themselves by means of conceptual analysis, although this knowledge can never be as clear and distinct as god's knowledge is. For Kant, by contrast, we can never have any knowledge of things in themselves at all, not even unclear or indistinct knowledge.

To understand why Kant believed this, we need to examine another fundamental break that he made with the rationalist tradition 11 years before writing the first Critique. In his Inaugural Dissertation of 1770, Kant distinguished between two basic faculties of the mind: understanding and sensibility. Understanding is the faculty of concepts, or general representations, whereas sensibility is the faculty of intuitions, or singular representations. Kant claims that we need both faculties for cognition, and that neither can be understood as a merely deficient form of the other. The Leibnizians were his targets here, as they understood sensibility as a merely confused form of understanding. That was how they made room for finite creatures like us with limited faculties of understanding to have some grasp of the world of metaphysical reality. We might not have god's perfect or intellectual understanding, but we do have a faculty that is fundamentally continuous with it—namely, a sensible understanding—which can be improved through conceptual analysis, granting us some knowledge of metaphysical reality.

By rejecting this single-spectrum theory of the relation between understanding and intuition, Kant foreclosed on the possibility of knowing things in themselves. This is because the understanding requires intuitions to work on in order to produce cognition, but our sensible faculty of intuition is passive with respect to its matter. That is, it can only receive its contents as a result of being affected by things in themselves; it cannot actively grasp them as they are in themselves. In other words, we can only know things as they appear to us or as they are in the phenomenal world, not as they are in the world of things in themselves. Rather than drawing a continuum between knowledge of the phenomenal and metaphysical worlds like Leibniz did, Kant placed a precise barrier between the two. The project of placing this barrier and investigating its implications for knowledge is what Kant means by “transcendental.”

Armed with this understanding of the first term in “transcendental idealism,” we can now return to the second and see how Kant's idealism is fundamentally different from Leibniz'. What is ideal in transcendental idealism are the spatiotemporal and conceptual forms that objects in the phenomenal world have as a result of interacting with formal features of our faculties of intuition and understanding. The matter we use to constitute phenomenal objects is not ideal—it comes from things in themselves affecting our faculty of intuition—but in order for us to form a cognition on the basis of that matter, it must pass through the spatiotemporal forms of our intuition and the fundamental conceptual forms of our understanding. This makes the resulting object (the phenomenal object, the object of our cognition or knowledge) ideal in the sense that its form depends on features of the human mind. Whereas for Leibniz both the form and the matter of the phenomenal world are ideal, for Kant only the form is ideal; the matter is "real" in the sense that it is given by the thing in itself. This is the essence of transcendental idealism.

So how does transcendental idealism help Kant achieve his fundamental aim of explaining the possibility of synthetic a priori cognition? The answer lies in what is called Kant's "Copernican turn," which Kant describes in the introduction to the second edition of the Critique as follows:

"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."

What Kant's suggesting is that we use what we've just discussed about transcendental idealism as the grounds for a fundamental reorientation of philosophy comparable to Copernicus' revolution in astronomy. Just as Copernicus reoriented the center of the universe from the earth to the sun, Kant was suggesting that we reorient philosophy from a position that takes objects as they are in themselves as its starting point to one which takes human cognitive capacities as its starting point. Rather than attempting to cognize things in themselves—which we've just seen to be impossible, and which leads to the dogmatic excesses of the rationalists—philosophy, Kant suggests, should turn instead to investigating the cognition of objects of experience, or what I've been calling phenomenal objects.

Because these objects are formally ideal—because they depend on forms of the human mind—they are in a sense "ours," and that allows us to know truths about them a priori, including synthetic truths. The rationalists' attempt to justify synthetic a priori cognition fails because they have no way of explaining why it is that the objects they are concerned with (things in themselves) should conform to anything accessible a priori to humans. If the objects rationalists are concerned with exist independently of the human mind, what grounds do we have for believing that they conform to innate ideas in the mind? Our innate ideas, if such things exist at all, might just as well be what Kant calls "chimeras of the brain," totally unrelated to things in themselves.

If, however, the objects of philosophy are not things in themselves but rather things as they appear to us, or phenomena, this danger disappears. Because these objects are produced in accordance with the forms of our mind, we can cognize them using those same forms. If some forms of the mind are necessary to have any experience of objects at all, then they must be accessible to us a priori—otherwise we wouldn't be able to have any experience with which to acquire them—and thus we can use them to attain synthetic a priori knowledge. The bulk of the Critique is dedicated to exploring precisely this possibility, that is, to showing that certain forms of intuition and understanding are necessary for experience, and therefore do provide us with synthetic a priori cognition.