transforms into a metaphysical substance. His
theory of Ideas is the theory of the objectivity of concepts. That the
concept is not merely an idea in the mind, but something which has a
reality of its own, outside and independent of the mind--this is the
essence of the philosophy of Plato.

How did Plato arrive at this doctrine? It is founded upon the view
that truth means the correspondence of one's ideas with the facts of
existence. If I see a lake of water, and if there really is such a
lake, then my idea is true. But if there is no lake, then my idea is
false. It is an hallucination. Truth, according to this view, means
that the thought in my mind is a copy of something outside my mind.
Falsehood consists in having an idea which is not a copy of anything
which really exists. Knowledge, of course, means knowledge of the
truth. And when I say that a thought in my mind is knowledge, I must
therefore mean that this thought is a copy of something that exists.
But we have already seen that knowledge is the knowledge of concepts.
And if a concept is true knowledge, it can only be true in virtue of
the fact that it corresponds to an objective reality. There must,
therefore, be general ideas or concepts, outside my mind. It were a
contradiction to suppose, on the one hand, that the concept is true
knowledge, and on the other, that it corresponds to nothing external
{184} to us. This would be like saying that my idea of the lake of
water is a true idea, but that no such lake really exists. The concept
in my mind must be a copy of the concept outside it.

Now if knowledge by concepts is true, our experiences through
sensation must be false. Our senses make us aware of many individual
horses. Our intellect gives us the concept of the horse in general. If
the latter is the sole truth, the former must be false. And this can
only mean that the objects of sensation have no true reality. What has
reality is the concept; what has no reality is the individual thing
which is perceived by the senses. This and that particular horse have
no true being. Reality belongs only to the idea of the horse in
general.

Let us approach this theory from a somewhat different direction.
Suppose I ask you the question, "What is beauty?" You point to a rose,
and say, "Here is beauty." And you say the same of a woman's face, a
piece of woodland scenery, and a clear moonlight night. But I answer
that this is not what I want to know. I did not ask what