This theory is supposed to be based on Aristotle's Metaphysics, a passage containing an account of the ideas, which hitherto scholars have found impossible to reconcile with the statements of Plato himself. The preparations for the new departure are discovered in the Parmenides and in the Theaetetus; and it is said to be expressed under a different form by the (Greek) and the (Greek) of the Philebus. The (Greek) of the Philebus is the principle which gives form and measure to the (Greek); and in the 'Later Theory' is held to be the (Greek) or (Greek) which converts the Infinite or Indefinite into ideas. They are neither (Greek) nor (Greek), but belong to the (Greek) which partakes of both. With great respect for the learning and ability of Dr. Jackson, I find myself unable to agree in this newly fashioned doctrine of the Ideas, which he ascribes to Plato. I have not the space to go into the question fully; but I will briefly state some objections which are, I think, fatal to it. (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.)