We can only explain it, said Kant, in this way: We must assume that what is given us from without is merely the raw material of sensation, the _matter_ of our experience; and that the ordering of this matter, the arranging it into a world of phenomena, the furnishing of _form_, is the work of the mind. Thus, we must think of space, time, causality, and of all other relations which obtain between the elements of our experience, as due to the nature of the mind. It perceives the world of phenomena that it does, because it _constructs_ that world. Its knowledge of things is stable and dependable because it cannot know any phenomenon which does not conform to its laws. The water poured into a cup must take the shape of the cup; and the raw materials poured into a mind must take the form of an orderly world, spread out in space and time. Kant thought that with this turn he had placed human knowledge upon a satisfactory basis, and had, at the same time, indicated the limitations of human knowledge. If the world we perceive is a world which we make; if the forms of thought furnished by the mind have no other function than the ordering of the materials furnished by sense; then what can we say of that which may be beyond phenomena? What of _noumena_? It seems clear that, on Kant's principles, we ought not to be able to say anything whatever of _noumena_. To say that such may exist appears absurd. All conceivable connection between them and existing things as we know them is cut off. We cannot think of a noumenon as a _substance_, for the notions of substance and quality have been declared to be only a scheme for the ordering of phenomena. Nor can we think of one as a cause of the sensations that we unite into a world, for just the same reason. We are shut up logically to the world of phenomena, and that world of phenomena is, after all, the successor of the world of ideas advocated by Berkeley. This is not the place to discuss at length the value of Kant's contribution to philosophy.[3] There is something terrifying in the prodigious length at which it seems possible for men to discuss it. Kant called his doctrine "Criticism," because it undertook to establish the nature and limits of our knowledge. By some he has been hailed as a great enlightener, and by others he has been accused of being as dogmatic in his assumptions as those whom he disapproved. But one thing he certainly has accomplished. He has made the words "phenomena" and "noumena" familiar to us all, and he has induced a vast number of men to accept it as established fact that it is not worth while to try to extend our knowledge beyond phenomena. One sees his influence in the writings of men who differ most widely from one another. [1] "Essay," Book IV, Chapter XI, section 7. [2] "An Inquiry into the Human Mind," Chapter V, section 5. [3] The reader will find a criticism of the Critical Philosophy in Chapter XV. CHAPTER XIII REALISM AND IDEALISM