According to this, the outer object is not known through an inference; it is known directly. But do not be in haste to class Spencer with the plain man, or with Reid. Listen to a citation once before made (section 22), but worth repeating in this connection: "When we are taught that a piece of matter, regarded by us as existing externally, cannot be really known, but that we can know only certain impressions produced on us, we are yet, by the relativity of thought, compelled to think of these in relation to a cause--the notion of a real existence which generated these impressions becomes nascent. If it be proved that every notion of a real existence which we can frame is inconsistent with itself,--that matter, however conceived by us, cannot be matter as it actually is,--our conception, though transfigured, is not destroyed: there remains the sense of reality, dissociated as far as possible from those special forms under which it was before represented in thought." It is interesting to place the two extracts side by side. In the one, we are told that we do not know external objects by an inference from our sensations; in the other we are taught that the piece of matter which we regard as existing externally cannot be really known; that we can know only certain impressions produced on us, and must refer them to a cause; that this cause cannot be what we think it. It is difficult for the man who reads such statements not to forget that Spencer regarded himself as a realist who held to a direct knowledge of something external. There are, as it is evident, many sorts of realists that may be gathered into the first class mentioned above--men who, however inconsistent they may be, try, at least, to maintain that our knowledge of the external world is a direct one. And it is equally true that there are various sorts of realists that may be put into the second class. These men have been called _Hypothetical Realists_. In the last chapter it was pointed out that Descartes and Locke belong to this class. Both of these men believed in an external world, but believed that its existence is a thing to be inferred. Now, when a man has persuaded himself that the mind can know directly only its own ideas, and must infer the world which they are supposed to represent, he may conceive of that external world in three different ways.