Kant, Immanuel (1724-1804). German philosopher, one of the most important thinkers (along with Plato, Aristotle, Thomas Aquinas, and Descartes) in the history of Western thought, and exercising a profound influence on Christian theology, especially within the Reformation heritage. Born in Königsberg (now Kaliningrad), East Prussia, where also he died, he never traveled beyond it, holding until his death his professorship of logic at the University of Königsberg, to which he had been appointed in 1770 ( Privatdozent 1755-1770).

In a very general way he may be considered, in the context of his age, as having synthesized the British Empiricist and the Continental European Rationalist schools of philosophy by asking neither what we know about the universe nor what is the nature of the universe, but, rather: What is possible for the human mind to know? Although his philosophy is primarily critical in the sense that he critically examines the limits of human knowledge, he ends by showing why a certain kind of knowledge is possible and what such knowledge attains.

He starts with traditional distinctions to be found in Leibniz (in whose system Kant was trained) between analytic and synthetic propositions and between a priori and a posteriori ones. Analytic propositions do not tell us anything new; for example, "all stallions are male" tells us nothing new, for a stallion is nothing other than a male horse. Mathematical propositions are of this kind: they analyze the implicates of what is already known within a system but may need extrapolation. One does not need to look at the external world to deal with them. Synthetic propositions, by contrast, purport to add some knowledge for the ascertaining of which we have to look at the external world. Analytic propositions are a priori in the sense that what they assert is known to be true or false before experience; synthetic propositions are a posteriori in the sense that they cannot be said to be known except after experience. For example, there is no use your telling me about kangaroos till I have seen one or at least a picture of one. Kant asks, then, whether there can be any synthetic propositions that are a priori, that is, that do not require experience, and much of his philosophy consists in a demonstration of how this could be. There are realities to be known, but what we can actually know is a combination of these realities with the mind that is engaged in knowing them. I know the sun as a red ball in the sky that heats my body and can burn my skin. With a knowledge of physics and astronomy I can be more precise, but still I cannot know the sun "as it is in itself" (the Dt'ng an Sich). Nevertheless, I am doing much better than merely recording my sensations.

Such are the kinds of question that Kant treats in his Critique of Pure Reason ( 1781). In the Critique of Practical Reason ( 1788) he sought to show that the Ideas of Reason (God, Freedom, Immortality), although not theoretically demonstrable, are nevertheless warranted in practice. Various implicates of this view are exhibited in his Critique of Judgment ( 1790), and some theological questions are raised in his Religion within the Limits of Reason ( 1793).

Although Kant's philosophy was deeply respectful of traditional belief in God and provided a basis for justifying faith as understood within the Reformation heritage, he left no quarter for the Catholic view as expounded in the seminaries that the existence of God could be proved by rational argument. He repudiated the Ontological Argument as offered by Descartes. Thomas Aquinas had repudiated that argument in the form in which it had been presented much earlier by Anselm and had provided instead five others, which he modestly called "ways" (viae) pointing to the existence of God. Kant, however, rejected all of these as unwarranted, although he recognized belief in God to be warranted by the "practical reason."

While Kant's thought has played an enormous role not only in Western philosophy in general but in the development of philosophical theology within the Reformation heritage, it was for long resisted in Roman Catholic circles. The Critique of Pure Reason was placed on the Index of Prohibited Books by papal decree of June 11, 1827, and was still included at least till the edition of the Index published in Vatican City in 1929.

Geddes MacGregor, Dictionary of Religion and Philosophy, New York: Paragon House, 1989