ABSTRACT
Common sense believes that we know something about mind, and something about matter; it holds, further, that what we know of both is enough to show that they are quite different kinds of things. I hold, on the contrary, that whatever we know without inference is mental, and that the physical world is only known as regards certain abstract features of its space-time structure—features which, because of their abstractness, do not suffice to show whether the physical world is, or is not, different in intrinsic character from the world of mind.
