Immanuel Kant: Critique of Pure Reason

Kant begins with the problem of metaphysics, which tends to overstep the boundaries of possible experience, producing dogmatic claims to knowledge and an unfortunate backlash in the form of skepticism and indifferentism. Kant proposes to police the proper limits of the employment of speculative reason through a “critique of pure reason,” a critique “of the faculty of reason in general, in respect of all knowledge after which it may strive independently of all experience.” Kant’s starting point is a fundamental distinction between the object as an appearance for us and the object as a thing in itself. All human knowledge has to do solely with the object as an appearance. We can have a priori knowledge about an object because, as an appearance for us, each object must conform to certain conditions in order to enter into our experience. This a priori knowledge is “independent of experience and even of all impressions of the senses,” and is to be distinguished from “empirical,” a posteriori knowledge. Kant’s transcendental philosophy aims to investigate and “determine the possibility, the principles, and the extent of all a priori knowledge.” The first section, the “Transcendental Aesthetic,” shows how time and space are “pure forms of sensible intuition” to which all possible objects of experience must conform. Kant isolates a “pure intuition” stripped of everything coming from the senses. The investigation of this pure intuition leads him to claim, “Space is a necessary a priori representation, which underlies all outer intuitions. We can never represent to ourselves the absence of space, though we can quite well think it as empty of objects.” He concludes, “space is nothing but the form of all appearances of outer sense. It is the subjective condition of sensibility under which alone outer intuition is possible for us.” But, he underscores, space is a predicate of things only as appearances for us, not in themselves. He then turns to investigate the other pure form of sensible intuition, time, and claims, “Time is a necessary representation that underlies all intuitions. We cannot, in respect of appearances in general, remove time itself, though we can quite well think time as void of appearances.” He concludes, “Time is the formal a priori condition of all appearances whatsoever.” Whereas the “Transcendental Aesthetic” is about the rules of sensibility, the next section, the “Transcendental Logic,” is about the rules of understanding, the faculty of thinking an object of sensible intuition. Kant writes, “Our knowledge springs from two fundamental sources of the mind; the first is the capacity for receiving representations (receptivity for impressions), the second is the power of knowing an object through these representations (spontaneity in the production of concepts). Through the first an object is given to us, through the second the object is thought in relation to that given representation. . . . Intuition and concepts constitute, therefore, the elements of all our knowledge, so that neither concepts without an intuition in some way corresponding to them, nor intuition without concepts, can yield knowledge.” More bluntly stated, “The understanding can intuit nothing, the senses can think nothing. Only through their union can knowledge arise.” The Transcendental Logic begins with the “transcendental analytic,” which examines the pure a priori concepts of understanding. Pure intuition provides a manifold, which is synthesized by the imagination. This synthesis then yields knowledge when brought to unity under the concepts of the understanding. From four initial categories, Kant derives 12 “pure concepts of understanding, which apply a priori to objects of intuition in general.” They are: (of quantity) unity, plurality, totality; (of quality) reality, negation, limitation; (of relation) inherence and subsistence, causality and dependence, community; (of modality) possibility-impossibility, existence-nonexistence, necessity-contingency. “The objective validity of the categories as a priori concepts rests . . . on the fact that, so far as the form of thought is concerned, through them alone does experience become possible. They relate of necessity and a priori to objects of experience, for the reason that only by means of them can any object whatsoever of experience be thought.” But Kant adds that a transcendental subject is still necessary: “There can be in us no modes of knowledge, no connection of unity of one mode of knowledge with another, without that unity of consciousness which precedes all data of intuitions and by relation to which representation of objects is alone possible. This pure original unchangeable consciousness I shall name transcendental apperception.” “The abiding and unchanging ‘I’ (pure apperception) forms the correlate of all our representations in so far as it is to be at all possible that we should become conscious of them.” In the next section, the “Transcendental Dialectic,” Kant aims to point out and correct errors stemming from the “deceptive extension of pure understanding.” But first, he examines the function of reason. According to Kant, reason works to bring “the understanding into thoroughgoing accordance with itself, just as the understanding brings the manifold of intuition under concepts and thereby connects the manifold.” The concepts of pure reason are “transcendental ideas,” which must be distinguished from the pure concepts of understanding. Kant emphasizes, “no object adequate to the transcendental idea can ever be found within experience.” Transcendental ideas act as guides for understanding, setting it the task of extending its unity toward the unconditioned. “Reason . . . occupies itself solely with the employment of understanding, not indeed in so far as the latter contains the ground of possible experience (for the concept of the absolute totality of conditions is not applicable to any experience, since no experience is unconditioned), but solely in order to prescribe to the understanding its direction towards a certain unity of which it has itself no concept, and in such manner as to unite all the acts of the understanding in respect of every object, into an absolute whole.” When examined by pure reason that remains within its appropriate limits, the three transcendental ideas—psychological, cosmological, and theological—form a system and lead one to assume “the purposive unity of things,” “to regard all order in the world as if it had originated in the purpose of a supreme reason.” To conclude: “Thus all human knowledge begins with intuitions, proceeds from thence to concepts, and ends with ideas. Although in respect of all three elements it possesses a priori sources of knowledge, which on first consideration seem to scorn the limits of all experience, a thoroughgoing critique convinces us that reason, in its speculative employment, can never with these elements transcend the field of possible experience, and that the proper vocation of this supreme faculty of knowledge is to use all methods, and the principles of these methods, solely for the purpose of penetrating to the innermost secrets of nature, in accordance with every possible principle of unity—that of ends being the most important—but never to soar beyond its limits, outside which there is for us nothing but empty space.”