Critique of Pure Reason by Immanuel Kant

First published:Kritik der reinen Vernunft, 1781 (English translation, 1838)

Type of work: Philosophy

The Work

Immanuel Kant’s Critique of Pure Reason is a masterpiece in metaphysics designed to explore the possibility of synthetic a priori judgments. A synthetic judgment is one whose predicate is not contained in the subject; an a priori judgment is one whose truth can be known independently of experience. Kant therefore in effect questioned how it is that statements in which the idea of the subject does not involve the idea of the predicate can nevertheless be true and can also be known to be true without recourse to experience.

To make the question clearer, Kant offered examples of analytic and synthetic judgments. The statement that “All bodies are extended” is offered as an analytic judgment because it would be impossible to think of a body, that is, a physical object, that was not spread out in space; the statement “All bodies are heavy” is offered as a synthetic judgment, because Kant believed that it is possible to conceive of a body without supposing that it has weight.

The judgment that “All red apples are apples” is analytic because it would be impossible to conceive that something that was red and an apple could possibly not be an apple; the predicate is, in this case, included in the subject. The judgment “All apples are red,” however, is synthetic, because it is possible to think of an apple without supposing it to be red; in fact, some apples are green. Synthetic judgments can be false, but analytic judgments are never false.

A priori knowledge is knowledge “absolutely independent of all experience,” whereas a posteriori knowledge is empirical knowledge, that is, knowledge possible only through experience. Human beings can know a priori that all red apples are apples (and that they are red), but to know that a particular apple has a worm in it is something that can be known only a posteriori.

The question whether synthetic a priori judgments are possible concerns judgments that must be true—because they are a priori and can be known to be true without reference to experience—even though, being synthetic, their predicates are not conceived in thinking of their subjects. As an example of a synthetic a priori judgment Kant offers the statement “Everything that happens has its cause.” He argues that he can think of something happening without considering whether it has a cause; the judgment is, therefore, not analytic. Yet he supposes that it is necessarily the case that everything that happens has a cause, even though his experience is not sufficient to support that claim. The judgment must be a priori. How are such synthetic a priori judgments possible?

One difficulty arises at this point. Critics of Kant have argued that Kant’s examples are not satisfactory. The judgment that everything that happens has a cause is regarded either as being an analytic rather than a synthetic a priori judgment (every event being a cause relative to an immediately subsequent event, and an effect relative to an immediately preceding event) or as being a synthetic a posteriori rather than an a priori judgment (which leaves open the possibility that some events may be uncaused). A great many critics have maintained that Kant’s examples are bound to be unsatisfactory for the obvious reason that no synthetic a priori judgments are possible. The argument is that unless the predicate is involved in the subject, the truth of the judgment is a matter of fact, to be determined only by reference to experience.

Kant’s answer to the problem concerning the possibility of synthetic a priori judgments that pure reason—that is, the faculty of arriving at a priori knowledge—is possible because the human way of knowing determines, to a considerable extent, the character of what is known. Whenever human beings perceive physical objects, they perceive them in time and space; time and space are what Kant calls “modes of intuition,” that is, ways of apprehending the objects of sensation. Because human beings must perceive objects in time and space, the judgment that an object is in time must be a priori but, provided the element of time is no part of the conception of the object, the judgment is also synthetic. It is somewhat as if a world were being considered in which all human beings were compelled to wear green glasses. The judgment that everything seen is somewhat green would be a priori (since nothing could be seen except by means of the green glasses), but it would also be synthetic (since being green is no part of the conception of object).

In Kant’s terminology, a transcendental philosophy is one concerned not so much with objects as with the mode of a priori knowledge, and a critique of pure reason is the science of the sources and the limits of what contains the principles by which human beings know a priori. Space and time are the forms of pure intuition, that is, modes of sensing objects. The science of all principles of a priori sensibility, that is, of those principles that make a priori intuitions (sensations) possible, Kant calls the transcendental aesthetic.

Human beings do more than merely sense or perceive objects; they also think about them. The study of the existence of a priori concepts, as distinguished from intuitions, is called transcendental logic. This study is divided into transcendental analytic, dealing with the principles of the understanding without which no object can be thought, and transcendental dialectic, showing the error of applying the principles of pure thought to objects considered in themselves.

Using Aristotle’s term, Kant calls the pure concepts of the understanding categories. The categories are of quantity (unity, plurality, totality), quality (reality, negation, limitation), relation (substance and accident, cause and effect, reciprocity between agent and patient), and modality (possibility-impossibility, existence-nonexistence, necessity-contingency). According to Kant, everything that is thought is considered according to these categories. It is not a truth about things in themselves that they are one or many, positive or negative, but that all things fall into these categories because the understanding is so constituted that it can think in no other way.

Kant maintained that there are three subjective sources of the knowledge of objects: sense, imagination, and apperception. By its categories, the mind imposes a unity on the manifold of intuition; what would be a mere sequence of appearances, were the mind not involved, makes sense as the appearance of objects.

The principles of pure understanding fall into four classes: axioms of intuition, anticipations of perception, analogies of experience, and postulates of empirical thought in general. The principle of the axioms of intuition is that “All intuitions are extensive magnitudes,” proved by reference to the claim that all intuitions are conditioned by the spatial and temporal mode of intuition.

The principle by which all perception is anticipated is that “the real that is an object of sensation has intensive magnitude, that is, a degree.” It would not be possible for an object to influence the senses to no degree; hence, various objects have different degrees of influence on the senses. The principle of the analogies of experience is that “Experience is possible only through the representation of a necessary connection of perceptions.” Human experience would be meaningless were it not ordered by the supposition that perceptions are of causally related substances that are mutually interacting.

Kant’s postulates of empirical thought in general relate the possibility of things to their satisfying the formal conditions of intuition and of concepts, the actuality of things to their satisfying the material conditions of sensation, and the necessity of things to their being determined “in accordance with universal conditions of experience” in their connection with the actual.

A distinction that is central in Kant’s philosophy is the distinction between the phenomenal and the noumenal. The phenomenal world is the world of appearances, the manifold of sensation as formed spatially and temporally and understood by use of the categories. The noumenal world is the world beyond appearance, the unknown and unknowable, the world of “things-in-themselves.”

In the attempt to unify experience, reason constructs certain ideas—of a soul, of the world, of God. These ideas are, however, transcendental in that they are illegitimately derived from a consideration of the conditions of reason. To rely on them leads to difficulties that Kant’s “Transcendental Dialectic” was designed to expose. The “Paralogisms of Pure Reason” are fallacious syllogisms for which the reason has transcendental grounds; that is, the reason makes sense out of its operations by supposing what, on logical grounds, cannot be admitted. The “Antinomies of Pure Reason” are pairs of contradictory propositions, all capable of proof provided the arguments involve illegitimate applications of the forms and concepts of experience to matters beyond experience.

Kant concludes the Critique of Pure Reason with the suggestion that the ideas of God, freedom, and immortality arise in the attempt to make moral obligation intelligible. This point was developed at greater length in his Grundlegung zur Metaphysik der Sitten (1785; Foundations of the Metaphysics of Morals, 1950) and his Kritik der praktischen Vernunft (1788; Critique of Practical Reason, 1873).

Bibliography

Allison, Henry E. Idealism and Freedom: Essays on Kant’s Theoretical and Practical Philosophy. New York: Cambridge UP, 1996. Print.

Bohman, James, and Matthias Lutz-Backmann, eds. Perpetual Peace: Essays on Kant’s Cosmopolitan Ideal. Cambridge: MIT P, 1997. Print.

Buroker, Jill Vance. Kant’s Critique of Pure Reason: An Introduction. New York: Cambridge UP, 2006. Print.

Cassirer, Ernst. Kant’s Life and Thought. Trans. James Hayden. New Haven: Yale UP, 1981. Print.

Caygill, Howard. A Kant Dictionary. Malden: Blackwell, 1995. Print.

Edgar, Scott. "The Explanatory Structure of the Transcendental Deduction and a Cognitive Interpretation of the First Critique." Canadian Jour. of Philosophy 40.2 (2010): 285–314. Print.

Griffith, Aaron M. "Perception and the Categories: A Conceptualist Reading of Kant's Critique of Pure Reason." European Jour. of Philosophy 20.2 (2012): 193–222. Print.

Guyer, Paul, ed. The Cambridge Companion to Kant. New York: Cambridge UP, 1992. Print.

Hare, John E. The Moral Gap: Kantian Ethics, Human Limits, and God’s Assistance. New York: Oxford UP, 1996. Print.

Kerr, Gaven. "Kant's Transcendental Idealism: A Hypothesis?" Intl. Philosophical Quarterly 51.2 (2011): 195–222. Print.

Kuehn, Manfred. Kant: A Biography. New York: Cambridge UP, 2001. Print.

Luchte, James. Kant’s Critique of Pure Reason: A Reader’s Guide. London: Continuum, 2007. Print.

Schönfeld, Martin. The Philosophy of the Young Kant: The Precritical Project. New York: Oxford UP, 2000. Print.

Schott, Robin May, ed. Feminist Interpretations of Immanuel Kant. University Park: Pennsylvania State UP, 1997. Print.

Walker, Ralph. Kant. New York: Routledge, 1999. Print.