Kant's chief inquiry is directed to the explanation of the certainty we have in the use of this category of cause to give us knowledge of what transcends experience. It is evident enough that experience cannot furnish us a knowledge of any universality in the facts of time or space and still less of any necessity of existence as prevailing among such facts. It can only say: "So far as observed this or that prevails."
Kant has done the cause of affirmative philosophy an incalculable service in showing the method of discovering the a priori elements in knowledge. But the use he made of his discoveries in rational psychology was to destroy the very foundations of philosophy and discourage any and all attempts to solve the great problems of human thought. For he held, first, that the considerable store of a priori knowledge which we have in possession is entirely subjective in its character: we do not know things-in-themselves but only phenomena and our own mental forms. We know the forms of our knowing to be the necessary forms for the existence of phenomena, because we impose those forms on the data of sensation.
Secondly, he held that our supposed transcendental knowledge, by which we reach the ideas of God, freedom, and immortality, is all an illusion. It is in fact only one side of a twofold argument—a conflict or antinomy of ideas either side of which seems to be irrefutably established when regarded by itself alone. For instance, the doctrine of causality seemed to contain the necessary implication of an original source of movement. That which causes, originates. That which receives and transmits causality is not a true cause but only an effect or at best an instrument or agent of the cause. Hence Plato and his school of thinkers could hold that a causality of mind or personality is involved as the ultimate presupposition of the least and most mechanical movement in the world.
Kant shows in his third antinomy that the line of thought which ends in discovering a free personality as the ultimate presupposition (the thesis), although it proceeds by logically necessary steps and is not fallacious, yet stands side by side with another line of thought equally necessary and logical and
