51.  THE CRITICAL PHILOSOPHY.—­The German philosopher, Immanuel Kant (1724-1804), was moved, by the skeptical conclusions to which Hume’s philosophy seemed to lead, to seek a way of escape, somewhat as Reid was.  But he did not take refuge in “Common Sense”; he developed an ingenious doctrine which has had an enormous influence in the philosophical world, and has given rise to a Kantian literature of such proportions that no man can hope to read all of it, even if he devotes his life to it.  In Germany and out of it, it has for a hundred years and more simply rained books, pamphlets, and articles on Kant and his philosophy, some of them good, many of them far from clear and far from original.  Hundreds of German university students have taken Kant as the subject of the dissertation by which they hoped to win the degree of Doctor of Philosophy;—­I was lately offered two hundred and seventy-four such dissertations in one bunch;—­and no student is supposed to have even a moderate knowledge of philosophy who has not an acquaintance with that famous work, the “Critique of Pure Reason.”

It is to be expected from the outset that, where so many have found so much to say, there should reign abundant differences of opinion.  There are differences of opinion touching the interpretation of Kant, and touching the criticisms which may be made upon, and the development which should be given to, his doctrine.  It is, of course, impossible to go into all these things here; and I shall do no more than indicate, in untechnical language and in briefest outline, what he offers us in place of the philosophy of Hume.

Kant did not try to refute, as did Reid, the doctrine, urged by Descartes and by his successors, that all those things which the mind directly perceives are to be regarded as complexes of ideas.  On the contrary, he accepted it, and he has made the words “phenomenon” and “noumenon” household words in philosophy.

The world which seems to be spread out before us in space and time is, he tells us, a world of things as they are revealed to our senses and our intelligence; it is a world of manifestations, of phenomena.  What things-in-themselves are like we have no means of knowing; we know only things as they appear to us.  We may, to be sure, talk of a something distinct from phenomena, a something not revealed to the senses, but thought of, a noumenon; but we should not forget that this is a negative conception; there is nothing in our experience that can give it a filling, for our experience is only of phenomena.  The reader will find an unmistakable echo of this doctrine in Herbert Spencer’s doctrine of the “Unknowable” and its “manifestations.”

Now, Berkeley had called all the things we immediately perceive ideas.  As we have seen, he distinguished between “ideas of sense” and “ideas of memory and imagination.”  Hume preferred to give to these two classes different names—­he called the first impressions and the second ideas.