Again, the physical sciences take the existence of matter for granted. But philosophy asks what matter is. At first sight it might appear that this question is one for the physicist and not the philosopher. For the problem of "the constitution of matter" is a well-known physical problem. But a little consideration will show that this is quite a different question from the one the philosopher propounds. For even if it be shown that all matter is ether, or electricity, or vortex-atoms, or other such, this does not help us in our special problem. For these theories, even if proved, only teach us that the different kinds of matter are forms of some one physical existence. But what we want to know is what physical existence itself is. To prove that one kind of matter is really another kind of matter does not tell us what is the essential nature of matter. That, therefore, is a problem, not of science, but of philosophy. In the same way, all the sciences take the existence of the universe for granted. But philosophy seeks to know why it is that there is a universe at all. Is it {6} true, for example, that there is some single ultimate reality which produces all things? And if so, what sort of a reality is it? Is it matter, or mind, or something different from both? Is it good or evil? And if it is good, how is it that there is evil in the world? Moreover every science, except the purely mathematical sciences, assumes the truth of the law of causation. Every student of logic knows that this is the ultimate canon of the sciences, the foundation of them all. If we did not believe in the truth of the law of causation, namely, that everything which has a beginning has a cause, and that in the same circumstances the same things invariably happen, all the sciences would at once crumble to dust. In every scientific investigation, this truth is assumed. If we ask the zoologist how he knows that all camels are herbivorous, he will no doubt point in the first instance to experience. The habits of many thousands of camels have been observed. But this only proves that those particular camels are herbivorous. How about the millions that have never been observed at all? He can only appeal to the law of causation. The camel's structure is such that it cannot digest meat. It is a case of cause and effect. How do we know that water always freezes at 0° centigrade (neglecting questions of pressure, etc.)? How do we know that this is true at those regions of the earth where no one has ever been to see? Only because we believe that in the same circumstances the same thing always happens, that like causes always produce like effects. But how do we know the truth of this law of causation itself? Science does not consider the question. It traces its assertions back to this law, but goes no {7} further. Its fundamental canon it takes for granted. The grounds of causation, why it is true, and how we know it is true, are, therefore, philosophical questions.