l are very exalted moral ideas, such as
beauty, justice, and goodness. But the case of whiteness will serve to
show that the theory attributes reality not only to exalted ideas, but
to others also. In fact, we might quite well substitute evil for
goodness, and all the same arguments would apply. Or we might take a
corporeal object such as the horse, and ask what "horse" means. It
does not mean the many individual horses, for since one word is used
it must mean one thing, which is related to individual horses, just as
whiteness is related to individual white things. It means the
universal horse, the idea of the horse in general, and this, just as
much as goodness or beauty, must be something objectively real.

Now beauty, justice, goodness, whiteness, the horse in general, are
all concepts. The idea of beauty is formed by including what is common
to all beautiful objects, and excluding those points in which they
differ. And this, as we have seen, is just what is meant by a concept.
Plato's theory, therefore, is that concepts are objective realities.
And he gives to these objective concepts the technical name Ideas.
This is his answer to the chief question of philosophy, namely, what,
amid all the appearances and unrealities of things, is that absolute
and ultimate reality, from which all else is to be explained? It
consists, for Plato, in Ideas.

Let us see next what the characteristics of the Ideas are. In the
first place, they are substances. Substance is a technical term in
philosophy, but its philosophical meaning is merely a more consistent
development of its {187} popular meaning. In common talk, we generally
apply the word substance to material things such as iron, brass, wood,
or water. And we say that these substances possess qualities. For
example, hardness and shininess are qualities of the substance iron.
The qualities cannot exist apart from the substances. They do not
exist on their own account, but are dependent on the substance. The
shininess cannot exist by itself. There must be a shiny something.
But, according to popular ideas, though the qualities are not
independent of the substance, the substance is independent of the
qualities. The qualities derive their reality from the substance. But
the substance has reality in itself. The philosophical use of the term
substance is simply a more consistent application of this idea.
Substance means, for the philosopher, that which has its whole being
in itself,