As of late, I’ve been working my way through a number of German idealist thinkers, producing a series of small posts as I investigate the tradition (see on Kant and Fichte here, on Fichte and Schelling here, and on Goethe here). In this post, I move back to Kant himself, sketching an outline of the critical philosophy, as expressed in The Critique of Pure Reason, including an account of his rejection of rationalism and empiricism, his account of intuitions, concepts, and ideas, and his notions of judgment, imagination, and apperception. Understanding Kant’s critical philosophy is essential to understanding the evolution of German idealism as a whole. As Frederick Beiser notes, those involved in this tradition strove to find a middle path between a number of competing binaries, including that between skeptical subjectivism and naive realism, foundationalism and relativism, materialism and idealism, and Platonism and historicism, binaries which, as Beiser rightly suggests, are still the concern of much contemporary epistemology.
In many ways, then, the attempt launched by Kant and the German idealists is centered on finding a synthesis between empirical reality and transcendental ideality. Kant’s hope was to create a new science (Wissenschaft) of knowledge through the transcendental method wherein metaphysics is recast in terms of the limits of human reason; this was a “critical idealism” that “observes the limits of human experience, and that avoids all speculation about the existence of spiritual substance.” Thus on the one hand Kant rejected Locke’s claims that the human being comes into the world as a blank slate (tabula rasa), that all ideas come to us through accrued sensory impressions, and that thinking is merely a reflection upon those ideas. On the other, Kant rejected Descartes’s account of the manner in which our imaginings (Vorstellen)—our representations of the real—coincide with things in their original being, or what Schelling calls “being through itself” (das von sich selbst Seyende).
Critical or transcendental idealism in this way sought to recognize the subjective, mental, and rational elements of the subject’s constructive capacity vis-a-vis experience whilst nevertheless rejecting the empiricists claims to individual solipsism and particularity. In this sense, the transcendental predicate of Kant’s idealism amounts to a universalism amongst humans (insofar as every human is a transcendental subject) which honored the intersubjective and publically observable elements of empirical experience (i.e., those elements which the special sciences describe). As Beiser notes, “The intersubjective world constituted by these concepts [of transcendental idealism] is not constructed from the ideas of the individual mind; rather, it is the necessary condition of even having such ideas.”
Thus for Kant it is the transcendental status of the subject’s construction of experience that secures both the epistemic role of reason in ordering concepts and the success of the empirical sciences in describing causal relationships within the domain of a shared intersubjective ideality. Crucially, the transcendental on this account, as Beiser is at pains to show, is not a new form of subjectivism, but an account of the space within which the subjective and the objective is established. This rational–empirical synthesis—the idea that mind actively organizes experience based on a priori principles, an idea that Lee Braver calls “the Kantian root” of modern philosophy—has dominated the continental landscape in one form or another for over 200 years.
More specifically, in his Critique of Pure Reason Kant argued that all knowledge, including our scientific knowledge, amounts to knowledge of appearances (phenomena) but never to things in themselves (noumena). These appearances are fashioned from our own representations. Kant wrote, “We suppose that our representations of things, as they are given to us, do not conform to these things as they are in themselves, but that these objects, as appearances, conform to our mode representation.”
To produce the representations that populate our first-person experience, Kant argued, sense impressions, or what he called intuitions, must be combined with concepts, which express our understanding of what is the case in a given moment of experience. As a singular representation, an intuition is a particular sensory item that provides sensibility with the raw data for conceptualization. On this account, a concept is a mode of synthesis in which the multiple and particular features of our sensory impressions are combined in a moment of cognition. For Kant, experience depends on receptivity, in the mode of sensible intuition, and discursivity, in the mode of conceptual ordering.
Concepts, Kant held, are deployed in our capacity for linking together multiple representations in a series of interconnected types. The concept takes an ideal type as an exemplar of a class of beings and compares the contents of our singular empirical encounters to this type, issuing a judgment in cognition about what the perceived item is as it emerges in perception. Stated differently, the judgment is the object’s emergence in perception. As Henry Allison notes, “To judge is both to unify representations by combining them in a concept (producing an analytic unity) and to relate these representations to an object in a manner that purports to be valid with respect to the object.”
Interestingly, for Kant, the imagination is central to his account of perception and judgment. On Kant’s account, the subject uses the conceptual tools acquired through experience—that is, through learning how to bring together representations into a concept—to project a likely future state of affairs based on our best understanding of an in-the-moment event. This understanding is rooted in our conceptual skills and knowledge, which yield to the subject relevant inferences about what to expect next in a given scenario. In this way, the given manifold of sensibility is not only combined through the understanding to produce a judgment, but also contains knowledge about a likely future event, constellated out of present actions. In Altman’s words, “According to Kant, the imagination forms expectations about our experience based on what we require of it conceptually; it relates the sensory manifold to conceptually possible future representations.”
On Kant’s view, then, the world—and what it might do next—is made intelligible only through our concepts and categories. This is the basis of Kant’s critical philosophy: All metaphysical description from this point on must be carried out in tandem with a transcendental epistemology, with a critical philosophy of the knowing person. In this sense, Kant recasts in a single move the modern senses of self, world, and knowledge. This move split the world into two complex registers, the noumenal and the phenomenal; it made truth an intersubjective agreement; and it positioned the self as an organizing center around which turned an epistemic anti-realism.
This organizing center Kant called the transcendental subject, a unity of apperception, a pure and unchanging consciousness who synthetically grounds and produces experience through the forms of intuition, the categories of the understanding, and the ideas of reason. These elements are transcendental in the sense of being anthropologically universal and they are formal in the sense of being necessary for our mode of experience; that is, the aim of Kant’s transcendental idealism is to provide an a priori account of the conditions of possibility necessary for experience.
In the context of transcendental idealism, what were for Aristotle ontological categories of being—quantity, quality, temporality, location, and so on—become epistemological categories in Kant’s critical philosophy. This shift amounts to a move away from metaphysical concepts of world and towards regulative ones. Specifically, with Kant’s Copernican Revolution, the notion of world is reduced to a regulative ideal used to clarify and systematize the ideas of reason. All previous metaphysical systems, including Aristotle’s, Kant argued, were but transcendental illusions, which the philosopher Sean Gaston aptly defined as any “subjective view that takes itself as an objective summation of things as they really are.” Gaston continues:
Before critical philosophy it was easier to speak of the world as something ontologically given. It was also easier to speak of a concept of world in general on this basis. Kant implies that there can be no concept of world in these terms and that we must use the idea of the world in general within the epistemological limitations and possibilities of reasoning.
The ideas of reason thus enable the understanding, even if only artificially, to extend beyond the immediately empirical. The regulative function of reason is thus to secure the understanding’s ability to issue judgments that hold consistently across time, allowing it to ground its operations beyond a series of fragmentary cognitions.
Kant further insists that the systematic unity that reason provides for the understanding’s various instances of cognition is merely projected; it is another transcendental illusion, albeit a necessary and functional one. The ideas here serve a similar function to the understanding that concepts serve to intuitions. Just as concepts gather together intuitions in a rule-like way, allowing for generality, consistency, and comparability in the plural contents of empirical experience across time, the ideas of reason gather together concepts in an equally rule-like way, permitting the recombination of concepts into new and more complex conceptual architectures.
Finally, as reason uses the concept of world to enable the understanding’s ability to make judgments across time and place, the transcendental unity of apperception grounds the thinking subject’s ability to maintain its sense of unity across moments of systematized understanding and intuiting. As a transcendental unity, this “I” is not equivalent to the empirical or psychological self, which may change moment to moment, but to the formal activity that synthesizes intuition, concept, and idea into a unity that transcends but connects together empirical instances of experience across time.
 Beiser, German Idealism, viii.
 Ibid., 36.
 Ibid., 43.
 Ibid., 18.
 Ibid., 20.
 See Braver, A Thing of This World, 3–11.
 Kant, Critique of Pure Reason, Bxx.
 Allison, Kant’s Transcendental Idealism, 81.
 Ibid., 14.
 Ibid., 80.
 Ibid., 84.
 Altman, “Legacies of German idealism,” 766.
 Braver, A Thing of This World, 8.
 Gaston, The Concept of World, 10.
 Ibid., 17.
 Allison, Kant’s Transcendental Idealism, 428–429.
 Ibid., 430.
 Ibid., 436.