They cannot be Distinguished
There is still a third difficulty in connexion with the dualistic theory; namely, the question how matter and mind are to be distinguished.
At first sight this question is ridiculous; for the whole theory consists of nothing but the clear and sharp distinction between the two. But it does not follow that this distinction is satisfactory. Matter is conceived as having one group of qualities, position and motion : mind as having a different group, thought and will.
Now we distinguish two different pieces of matter by their having different positions; and we distinguish mind from matter as a whole, presumably, by its having no position at all. But has mind really no position ? If that were the case, position would be irrelevant to consciousness as it is, for instance, to time; and my consciousness would be all over the universe precisely as 11.15 a.m. Greenwich time is all over the universe. But my consciousness is not all over the universe, if that means that I am equally conscious of all the universe at once; when I look out of the window, I see only Wetherlam, not Mont Blanc or the satellites of Sirius.
There may be, and doubtless is, a sense in which the mind rises above the limitations of space; but that is not to say that space is irrelevant to the mind.
It would appear, in fact, that things can only be distinguished when they are in some way homogeneous. We can distinguish two things of the same class or type without difficulty : we can point out that the difference lies in the fact that one weighs a pound and the other two pounds, or that one is red and the other blue.
Differentiating things implies comparing them: and if we are to compare things they must be comparable. If two things have no point of contact, they are not comparable, and therefore, paradoxical as it may seem, they cannot be distinguished. Now in our original definitions of mind and matter, there was no such community, no point of contact. Each was defined as having unique properties of its own, quite different in kind from the properties of the other : and if this is really so, to compare and distinguish them becomes impossible.
But in practice the dualistic view is more lenient than this. It is not at all uncommon to hear mind described as if it were a kind of matter; for instance, as a very subtle or refined matter : and it is equally common to hear matter spoken of as if it had that self-consciousness and power of volition which are characteristic of mind.
These are dismissed as confusions of thought, mythological and unscientific; but even if they cannot be defended they may be used as illustrations of the difficulty which mankind finds in keeping the ideas of matter and mind really separated. 89 Once grant that mind is a kind of matter, and it becomes for the first time possible to distinguish them; you have only to say what kind of matter mind is.
But, strictly interpreted, it seems that we can hardly accept the dualistic view whether as a metaphysic or as a hypothesis of science. It seems more hopeful to examine the other alternatives, materialism and idealism.