metaphysics in the Sophist, is not his explanation of 'Not-being' as
difference. With this he certainly laid the ghost of 'Not-being'; and we
may attribute to him in a measure the credit of anticipating Spinoza and
Hegel. But his conception is not clear or consistent; he does not
recognize the different senses of the negative, and he confuses the
different classes of Not-being with the abstract notion. As the Pre-
Socratic philosopher failed to distinguish between the universal and the
true, while he placed the particulars of sense under the false and
apparent, so Plato appears to identify negation with falsehood, or is
unable to distinguish them. The greatest service rendered by him to mental
science is the recognition of the communion of classes, which, although
based by him on his account of 'Not-being,' is independent of it. He
clearly saw that the isolation of ideas or classes is the annihilation of
reasoning. Thus, after wandering in many diverging paths, we return to
common sense. And for this reason we may be inclined to do less than
justice to Plato,--because the truth which he attains by a real effort of
thought is to us a familiar and unconscious truism, which no one would any
longer think either of doubting or examining.

IV. The later dialogues of Plato contain many references to contemporary
philosophy. Both in the Theaetetus and in the Sophist he recognizes that
he is in the midst of a fray; a huge irregular battle everywhere surrounds
him (Theaet.). First, there are the two great philosophies going back into
cosmogony and poetry: the philosophy of Heracleitus, supposed to have a
poetical origin in Homer, and that of the Eleatics, which in a similar
spirit he conceives to be even older than Xenophanes (compare Protag.).
Still older were theories of two and three principles, hot and cold, moist
and dry, which were ever marrying and being given in marriage: in speaking
of these, he is probably referring to Pherecydes and the early Ionians. In
the philosophy of motion there were different accounts of the relation of