(1) First, the foundation of his argument is laid in the Metaphysics of
Aristotle. But we cannot argue, either from the Metaphysics, or from any
other of the philosophical treatises of Aristotle, to the dialogues of
Plato until we have ascertained the relation in which his so-called works
stand to the philosopher himself. There is of course no doubt of the great
influence exercised upon Greece and upon the world by Aristotle and his
philosophy. But on the other hand almost every one who is capable of
understanding the subject acknowledges that his writings have not come down
to us in an authentic form like most of the dialogues of Plato. How much
of them is to be ascribed to Aristotle's own hand, how much is due to his
successors in the Peripatetic School, is a question which has never been
determined, and probably never can be, because the solution of it depends
upon internal evidence only. To 'the height of this great argument' I do
not propose to ascend. But one little fact, not irrelevant to the present
discussion, will show how hopeless is the attempt to explain Plato out of
the writings of Aristotle. In the chapter of the Metaphysics quoted by Dr.
Jackson, about two octavo pages in length, there occur no less than seven
or eight references to Plato, although nothing really corresponding to them
can be found in his extant writings:--a small matter truly; but what a
light does it throw on the character of the entire book in which they
occur! We can hardly escape from the conclusion that they are not
statements of Aristotle respecting Plato, but of a later generation of
Aristotelians respecting a later generation of Platonists. (Compare the
striking remark of the great Scaliger respecting the Magna Moralia:--Haec
non sunt Aristotelis, tamen utitur auctor Aristotelis nomine tanquam suo.)

(2) There is no hint in Plato's own writings that he was conscious of
having made any change in the Doctrine of Ideas such as Dr. Jackson
attributes to him, although in the Republic the platonic Socrates speaks of