All modern philosophy is a footnote to Kant [or perhaps to Descartes], as all philosophy is a footnote to Plato. Kant is deservedly considered a great philosopher. Charles Murray puts him at number 3 in the list of the 100 most eminent philosophers. However, Kant is unusual among philosophers in having a major element of his philosophy refuted by later experimentation. Sure, sure, I hear you reciting examples of things Aristotle got wrong, like gravity. Nothing important in Aristotle's physics has been refuted. If anything, it is experiencing a resurgence. Kant's natural philosophy is radically at odds with quantum mechanics and general relativity alike.
However, the real thrust of Kant's philosophy was ethics, and this is were Kant retains enormous influence.
Kant's solution to the question of the origin of moral obligation was wonderfully ingenious, though historically catastrophic. In effect, his guiding question is not, "What would Jesus do?" but "What would I do if I were God?"
The modern turn in Kant's philosophy was to make the will the font of morality. Much later mischief has come of this.
Critique of Pure Reason
by Immanuel Kant
First Edition 1781; Second Edition 1787
Translation by F. Max Müller (1881)
Anchor Doubleday Paper Edition 1966
543 Pages, $1.95
"Immanuel admitted, as a speculative truth, that there were such things as dreams, and that he conceivably dreamed himself: but then he had a complex proof (which John never quite grasped) that no one could possibly remember a dream..." C.S. Lewis The Pilgrim's Regress Page 132
All modern philosophy is a footnote to this book by Immanuel Kant (1724-1804), professor of the University of Königsberg and, by some accounts, the most boring man who ever lived. If we hold up the "Critique" to a light, we can see all kinds of creatures in embryo: Hegel's historicism, Marx's dialectical materialism, Nietzsche's Triumph of the Will, as well as such later hatchlings as Pragmatism, Logical Positivism, and Mathematical Intuitionism. There is even, perhaps, a hint of the feral supernatural that we see in the fiction of H.P. Lovecraft, which is a very late product of New England Transcendentalism. Kant's Transcendental Idealism is one of the great philosophies, fruitful even when it is wrong. Such systems are never simply refuted. Nonetheless, looking at the Critique from the beginning of the 21st century, it is clear that Kant was too pessimistic about the possible scope of human knowledge. It is also clear that, oddly enough, he had nothing to say about the real limits of pure reason.
The problem with writing about Kant is that the inherent difficulties of his philosophy are in no way mitigated by its appalling exposition. Maybe the old translation I used was more Germanic than necessary, but Kant has been blamed for inaugurating the tradition of philosophical bad prose. Kant was in fact capable of lucid writing; he even had a sense of humor. Nonetheless, the "Critique of Pure Reason," the most important of his books, is full of sentences like this: "But is it really necessary that, if effects are phenomena, the causality of their cause, which cause itself is phenomenal, could be nothing but empirical; or is it not possible, although for every phenomenal effect a connection with its cause, according to the laws of empirical causality, is certainly required, that empirical causality itself could nevertheless, without breaking in the least its connection with the natural causes, represent an effect of a non-empirical and intelligible causality, that is, of a caused action, original in respect to phenomena, and in so far not phenomenal: but, with respect to this faculty, intelligible, although, as a link in the chain of nature, to be regarded as entirely belonging to the world of sense?" (Page 372)