a rather important part in Kant's philosophy. He had a series of arguments which he believed to be perfectly valid from the ordinary point of view and which proved that the universe must be finite in space and time; and he had another set of arguments on the opposite page which proved that the universe must necessarily be infinite in both respects. He believed that there was a real contradiction between these two proofs, which could be overcome only by his own philosophy with its distinction between the world as appearance and the world as reality. Again modern scince, discarding entirely Kant's merely speculative reason, has very definite arguments in favor of the view that the universe is finite in space. There are in the first place astronomical reasons which give a certain probability to this view, but there are also general reasons derived from the application of modern physics to problems concerning the structure of the universe which seem almost inevitably to lead to the conclusion that the universe must be finite in space, though probably not in time. The proof will rest on astronomical observations and our knowledge of the laws of nature and on nothing else.
This case is similar to the one of the former question in that the problem seems to be shifted from the realm of philosophical speculation to that of scientific observation, thereby changing from an apparently hopeless issue into a perfectly answerable question. With the development of our knowledge we come to see possibilities which formerly were not known to men; and therefore the number of insoluble problems seems to diminish. What is the significance of this process, and can it go on indefinitely?
Now let us consider another “purely philosophical” problem, one of the oldest in philosophy; the “relationship between body and mind.” Are there perhaps two substances in the world, physical and mental substance; and what is their interaction? Is there any such thing as mind, or must everything be explained in terms of physics? Is there any such thing as matter, or must everything be explained in terms of mind? Such are the questions about which philosophers have debated. Concerning this particular problem, not a few of them have taken the attitude that it is a good instance of an unanswerable question. They say, for instance, that there will never be the slightest hope of understanding even the simplest act of sensation.
They argue that it is impossible to imagine any way in which a certain physical process in the brain can be transformed into a sensation, i. e. into
