The keystone of Kant’s philosophy, sometimes called critical philosophy, is contained in his Critique of Pure Reason (1781), in which he examined the bases of human knowledge and created an individual epistemology. Like earlier philosophers, Kant differentiated modes of thinking into analytic and synthetic propositions. An analytic proposition is one in which the predicate is contained in the subject, as in the statement “Black houses are houses.” The truth of this type of proposition is evident, because to state the reverse would be to make the proposition self-contradictory. Such propositions are called analytic because truth is discovered by the analysis of the concept itself. Synthetic propositions, on the other hand, are those that cannot be arrived at by pure analysis, as in the statement “The house is black.” All the common propositions that result from experience of the world are synthetic.
Propositions, according to Kant, can also be divided into two other types: empirical and a priori. Empirical propositions depend entirely on sense perception, but a priori propositions have a fundamental validity and are not based on such perception. The difference between these two types of proposition may be illustrated by the empirical “The house is black” and the a priori “Two plus two makes four.” Kant’s thesis in the Critique is that it is possible to make synthetic a priori judgments. This philosophical position is usually known as transcendentalism. In describing how this type of judgment is possible Kant regarded the objects of the material world as fundamentally unknowable; from the point of view of reason, they serve merely as the raw material from which sensations are formed. Objects of themselves have no existence, and space and time exist only as part of the mind, as “intuitions” by which perceptions are measured and judged.
In addition to these intuitions, Kant stated that a number of a priori concepts, which he called categories, also exist. He divided the categories into four groups: those concerning quantity, which are unity, plurality, and totality; those concerning quality, which are reality, negation, and limitation; those concerning relation, which are substance-and-accident, cause-and-effect, and reciprocity; and those concerning modality, which are possibility, existence, and necessity. The intuitions and the categories can be applied to make judgments about experiences and perceptions, but cannot, according to Kant, be applied to abstract ideas such as freedom and existence without leading to inconsistencies in the form of pairs of contradictory propositions, or “antinomies,” in which both members of each pair can be proved true.
In the Metaphysics of Ethics (1797) Kant described his ethical system, which is based on a belief that the reason is the final authority for morality. Actions of any sort, he believed, must be undertaken from a sense of duty dictated by reason, and no action performed for expediency or solely in obedience to law or custom can be regarded as moral. Kant described two types of commands given by reason: the hypothetical imperative, which dictates a given course of action to reach a specific end; and the categorical imperative, which dictates a course of action that must be followed because of its rightness and necessity. The categorical imperative is a three-pronged statement that succinctly outlines Kant’s moral views. All three must be met for an action to be morally obligatory.
Formulation One-“Act according to that maxim by which you can at the same time will that it should become a universal law.” Or, “Think about what would happen if everyone acted in the same way, and for the same reasons you did.”
All moral laws must be universal. They are formed regardless of circumstance, since the circumstances cannot be predicted. All we can really know is the principle behind our action. Besides this, the consequences do not matter. If something is deemed to be moral, it becomes a duty. A duty must be fulfilled, no matter what the consequences. For example, making a false promise, a man in need finds himself forced to borrow money. He knows that he cannot repay, but promises to do so anyway. His maxim is “when I believe myself to be in need of money, I will borrow money and promise to repay it, though I know I cannot.” If it were universalized, this law of false promises destroys the entire concept of promises, since no person would believe anyone. It is thus immoral, since it cannot rationally be universalized.
Formulation Two-“Act so that you treat humanity, whether in you own person, or that of another, as an end and never as a means only.” Or, “Don’t use people.”
Humans all possess rationality, this gives them inherent worth. All humans must be treated as ends in every circumstance. This formulation says that the ends of others, if morally permissible, set limits to the ends that we can pursue. We must respect the permissible ends of others, and we may make people serve our purposes only when they, as moral agents, consent to such use. For example, a worker is used as a means to the economic strength of his employer, but he agrees to his use, is paid, and is treated with respect, so he is also an end in and of himself.
Formulation Three-“All maxims as proceeding from our own lawmaking ought to harmonize with a possible kingdom of ends as a kingdom of nature.”
Here we are told to think of ourselves as members of a society of beings whose permissible ends are to be respected. We must test our maxims by asking whether, supposing the maxims were universal laws, there would be a society of that kind. We must look at both the agent and the ricipient of the action together in a community as we legislate through our laws.
Kant’s ethical ideas are a logical outcome of his belief in the fundamental freedom of the individual as stated in his Critique of Practical Reason (1788). This freedom he did not regard as the lawless freedom of anarchy, but rather as the freedom of self-government, the freedom to obey consciously the laws of the universe as revealed by reason. He believed that the welfare of each individual should properly be regarded as an end in itself and that the world was progressing toward an ideal society in which reason would “bind every law giver to make his laws in such a way that they could have sprung from the united will of an entire people, and to regard every subject, in so far as he wishes to be a citizen, on the basis of whether he has conformed to that will.” In his treatise, Perpetual Peace (1795) Kant advocated the establishment of a world federation of republican states.
Kant had a greater influence than any other philosopher of modern times did. Kantian philosophy, particularly as developed by the German philosopher G.W.F. Hegel, was the basis on which the structure of Marxism was built; the dialectical method, used by both Hegel and Karl Marx, was an outgrowth of the method of reasoning by “antinomies” that Kant used. The German philosopher Johann Fichte, Kant’s pupil, rejected his teacher’s division of the world into objective and subjective parts and developed an idealistic philosophy that also had great influence on 19th-century socialists. One of Kant’s successors at the University of Knigsberg, J.F. Herbart, incorporated some of Kant’s ideas in his system of pedagogy.