The question which Kant put at the beginning of his philosophy, namely 'How is pure mathematics possible'? is an interesting and difficult one, to which every philosophy which is not purely sceptical must find some answer.
Thus according to the philosophers before Kant, the law of contradiction, which asserts that nothing can at the same time have and not have a certain property, sufficed to establish the truth of all a priori knowledge.
Other German philosophers also joined in the enterprise of transforming Kant's critical philosophy into a metaphysical idealism—most notably, Hegel, Schelling, and Schopenhauer.
13-3Kant's critical philosophy and his Copernican revolution The turning point in Kant's intellectual development was his encounter with Hume's empiricism.
14-4-3Phenomenal and Noumenal Reality A major aspect of Kant's critical philosophy was his insistence that human knowledge is forever limited in its scope.