Robert Solomon offers a helpful fairly traditional summary of Kant’s philosophy in his little book on Continental Philosophy. Kant’s overall agenda, Solomon says, was (in Kant’s own words) to “deny knowledge, in order to make room for faith.” Much as he admired the advances of post-Newtonian science, he worried that it could destroy the human world and religion. He wanted to show that religion and science could live together peaceably. Kant’s “Copernican Revolution” is worked out first in the Critique of Pure Reason. Metaphysics, Kant said, was “a battle-ground quite peculiarly suited for those who desire to exercise themselves in mock combats,” but no one has made any progress in metaphysics. Yet, metaphysics is unavoidable, particularly the questions of “God, freedom, and immortality.” Metaphysical questions such as the nature of the self, the reality of the world, the nature of mathematics, and the role of religion cannot be sidestepped. Kant was brought from his dogmatic slumber by the encounter with Hume, who concluded that we can’t really know the outside world at all. To meet the empiricism of Hume, it was necessary to turn the question around. Instead of asking how knowledge must conform to objects, Kant hoped to make progress by supposing that “objects must conform to knowledge.” He set out to demonstrate, in Solomon’s words, “The world IS the world of our experience, not something outside of it. We are not just acted upon by a world we never know directly; we act upon the world to give it its basic forms.

The Critique of Pure Reason is divided into three sections, which correspond to the three faculties of sense, understanding, and reason. Sense is “our capacity to be affected by sensations, to see, hear, smell, and feel.” Through understanding, we identify and organize sensations, connect them, employ concepts. Reason is the ability to fiddle with concepts wholly apart from experience. For Kant, each of these faculties has its own structure that “determines the nature of our experience.” He argues that “the human mind is responsible for the appearance of objects and their structures independent of us, even though we can come to appreciate, through reason, that this appearance of independence is dependent upon us.” Because of its ability to work without contact with the world, reason can get itself into trouble, and Kant’s work is partly an effort “to curb the historical pretensions of reason, and reason alone, to gain knowledge of God, eternity, and the nature of the world beyond the realm of our experience.”

Kant suggests “a new vision of human knowledge, a basic mode of knowledge that is something more than the passive reception and interpretation of sensations, and more substantial than the abstract manipulations of ideas.” This “a priori” knowledge and its principles rule our experience, and “the world has and must have the structures we impose upon it. “Transcendental” plays an important role in Kant’s philosophy. The term means “necessary and universal,” and the transcendental philosophy or transcendental idealism means essentially that “certain ideas are the basic (a priori) conditions for all possible human experience.” The first part of the first Critique is the Transcendental Aesthetic, which deals with the structures of sense experience. The “a priori forms of intuition” or sense experience are “space and time,” and the principles that govern sense experience are the principles of math and geometry. These principles “describe the basic structures of our experience itself.” This means, though, that the ego that imposes these forms on experience must itself be outside time: “It projects temporality but is not itself temporal.”

The Transcendental Analytic analyzes understanding, and introduces a list of 12 categories, “the most basic [concepts] such as the concept of an object as such, or the concept of one event causing another.” These are not learned from experience, but presupposed in every experience. They are transcendental categories, and they are again imposed by the transcendental ego: “We can know,” Kant says, “a priori of things only what we ourselves put into them.” Kant is not a solipsist. He is not that the world came into being when I started thinking about it The self brings the forms and the world supplies the given sensations that the world organizes. But the world as a set of organized objects is the product of this interaction. It should be remembered too that Kant’s self is not an empirical self, but the transcendental self that appears almost to be a universal shared self. Kant speaks of “consciousness in general,” which appears to stretch across the particular minds that participate in it.

The third part of the Critique of Pure Reason is the Transcendental Dialectic, which deals with the faculty of reason. He rejects the Cartesian notion that the self is a thinking thing, yet he also realizes that the self cannot be within human experience: Since it imposes the categories it cannot be subject to the categories. Kant also attacks traditional proofs of the existence of God, arguing that God is not within the realm of knowledge. This doesn’t mean that Kant is an atheist, or at least he professes not to be: “God remains for Kant a transcendental ideal, whose existence my not be a matter of knowledge but nevertheless is an absolutely necessary condition of human existence.” This portion of Kant’s treatise also introduces a series of antinomies, contradictory conclusions that can be equally supported by rational arguments. One can defend the proposition that the world is eternal, and the proposition that the world was created in time, and neither argument triumphs. The purpose of introducing the antinomies is to demonstrate “the illusory nature of reason.” This possibility of self-contradiction is not an accident, but built into the nature of reason. It is one way of showing the limits of reason, and making room for faith. Kant concludes that God, freedom, and immortality are not found within the realm of knowledge, but Kant’s purpose is not to dismiss these things. Rather, he wants to make room for faith and for the human, and it’s this effort that made Kant a precursor to the anti-rationalist movement of romanticism and certain strains of idealism.

The second Critique treats man not as a knower but as a doer. He is not only interested in man as an observer of the world, or with rationality. He wants to explain the character of the rational life. Morality cannot be left to sentimentality or to custom. It has to be rationally grounded, and has to be an expression of human rationality. And the second critique is the place where Kant most fully develops the contrast of the phenomenal world and the noumenal world, which he describes as the world “in itself.” It is not clear how the noumenal self is related to the transcendental ego that Kant posits in the first Critique, but he insists that this “two-world” system is essential to the possibility of morality. The problem is this: Newton and his followers have shown that the world is causally determined; yet, without freedom, there is not possibility for morality. There needs to be some way to secure the freedom of the self if it is going to act morally. Kant has already anticipated one part of the answer to this problem by his third antinomy: “every event has natural causes but some events do not” (Solomon’s summary).

For Kant, actions are “intentional, usually more or less deliberate, and implicitly based upon principles (or ‘maxims’), whether or not we act u ally think about these.” The maxims of the moral life are objective maxims, universal laws. The laws of morality are imperatives that lay out universal duties, and the imperative of all imperatives is the categorical imperative that “we should always act in such a way that the maxim behind our actions could be generalized as a universal law for everyone, and that we should always treat other people as ends in themselves, and never merely as means.” He imagines a “Kingdom of Ends,” a world in which everyone always acts rationally. The categorical imperative, and its social expression in the Kingdom of Ends, is an example of “pure” morality, stripped of custom, feeling, social influence, nurture, habit, and much else. Kant’s pattern of thought is consistent through the first Critiques. Necessary principles of knowledge are found independent of experience, and so also there are universal principles of action that are necessary and independent of context or inclination.

Solomon points to three crucial flaws in Kant’s approach to morality. First, Kant removes from consideration all the emotional components of morality: “compassion, sympathy, pleasure, satisfaction, and happiness.” What guides morality is simply one’s sense of duty, not sympathy for others. He favorably cites Nietzsche’s comment that “morality is anti-nature.” Second, Kant’s moral theory assumes a radical stance of autonomy: “Kant’s notion of knowledge is born of the Enlightenment faith in reason, the confidence that the individual can, using his own resources, through observation, experience, and careful thinking, discover what is true about the world. It is worth noting that there is no social element in this picture, no community of scientists, public opinion, or pressures from colleagues, employers, or research-granting agencies. Knowledge is purely a relationship between the autonomous individual and the world of nature, and morality is a relationship between the individual and the universal law, a product of pure practical reason.” Finally, Kant brings everything back to the inner self, particularly the will: “The only thing that is good without qualification,” Kant says, “is a good will.” What counts is not the consequences, but the intention and the maxim that guides action. Once again “the social is reduced to second-rate status,” and as a result “we lost what would seem to be the primary ground of ethics, our membership in a community and interaction with others.”