There is a story that Schopenhauer used to begin his lectures on Kant by saying: "Let no one tell you what is contained in the Critique of Pure Reason." The writer of this little book hopes that no one will imagine that he has disregarded this warning. There are no short-cuts to the understanding of a great philosopher, and the only way to appreciate the greatness of a philosophic system is to study the philosopher's own writings. All that the writer of a book like this can hope to do is to persuade others to undertake that study by interesting them in the problems with which it deals, and by offering a few suggestions which may help to an understanding of it. I have said nothing about the numerous other works which Kant wrote. For the three Critiques contain his system, and the understanding of that is all-important.