ory of Ideas is a
thing established, lead us to the belief that it belongs to the period
of Plato's maturity. Zeller's theory that it was written at the
beginning of the second period, and is then offered to the reader as a
sort of sweetmeat to induce him to enter upon the laborious task of
reading the "Sophist," the "Statesman," and the "Parmenides," seems to
be far-fetched and unnecessary. [Footnote 12]

[Footnote 12: Zeller's _Plato and the Older Academy_, chap. iii.]

If the second is the great constructive period of Plato's life, the
third may be described as his systematic and synthetic period. Every
part of his philosophy is here linked up with every other part. All
the details of the system are seen to flow from the one central
principle of his thought, the theory of Ideas. Every sphere of
knowledge and being is in turn exhibited in the light of that
principle, is permeated and penetrated by it.

The plan for expounding Plato which first suggests itself is to go
through the dialogues, one by one, and extract the doctrine of each
successively. But this suggestion has to be given up as soon as it is
mentioned. For although the philosophy of Plato is in itself a
systematic and coherent body of thought, he did not express it in a
systematic way. On the contrary, he scatters his ideas in all
directions. He throws them out at random in any order. What logically
comes first often appears last. It may be found at the end of a
dialogue, and the next step in reasoning may make its appearance at
the beginning, or even in a totally different dialogue. If, therefore,
we are to get any connected view of the system, we must abandon
Plato's own order of exposition, and piece the thought together for
ourselves. We must begin {177} with what logically comes first,
wherever we may find it, and proceed with the exposition in the same
manner.

A similar difficulty attends the question of the division of Plato's
philosophy. He himself has given us no single and certain principle of
division. But the principle usually adopted divides his philosophy
into Dialectic, Physics, and Ethics. Dialectic, or the theory of
Ideas, is Plato's doctrine of the nature of the absolute reality.
Physics is the theory of phenomenal existence in space and time, and
includes therefore the doctrine of the soul and its migrations, since
these are happenings in time. Ethics includes politics, the theory of
the duty of man as a citizen, as well as the eth