, 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.

(1) He may believe that what corresponds to his idea of a material
object, for example, an apple, is in very many respects like the idea
in his mind. Thus, he may believe that the odor, taste, color,
hardness, etc., that he perceives directly, or as ideas, have
corresponding to them real external odor, taste, color, hardness, etc.
It is not easy for a man to hold to this position, for a very little
reflection seems to make it untenable; but it is theoretically possible
for one to take it, and probably many persons have inclined to the view
when they have first been tempted to believe that the mind perceives
directly only its ideas.

(2) He may believe that such things as colors, tastes, and odors cannot
be qualities of external bodies at all, but are only effects, produced
upon our minds by something very different in kind. We seem to
perceive bodies, he may argue, to be colored, to have taste, and to be
odorous; but what we thus perceive is not the external thing; the
external thing that produces these appearances cannot be regarded as
having anything more than "solidity, extension, figure, motion or rest,
and number." Thus did Locke reason. To him the external world as it
really exists, is, so to speak, a paler copy of the external world as
we seem to perceive it. It is a world with fewer qualities, but,
still, a world with qualities of some kind.

(3) But one may go f