to fulfil all the functions involved in this definition. So, also, the creative cause of a man is another man, who directly impresses the human form on the material supplied by the female organism. In the same way, every definite individual aggregate becomes what it is through the agency of another individual representing the same type in its perfect manifestation.[228] The substantial forms of Aristotle, combining as they do the notion of a definition with that of a moving cause and a fulfilled purpose, are evidently derived from the Platonic Ideas; a reflection which at once leads us to consider the relation in which he stands to the spiritualism of Plato and to the mathematical idealism of the Neo-Pythagoreans. He agrees with them in thinking that general conceptions are the sole object of knowledge—the sole enduring reality in a world of change. He differs from them in maintaining that such conceptions have no existence apart from the particulars in which they reside. It has been questioned whether Aristotle ever really understood his master’s teaching on the subject. Among recent critics, M. Barthélemy Saint-Hilaire asserts, with considerable vehemence, that he did not. It is certain that in some respects Aristotle is not just to the Platonic theory, that he exaggerates its absurdities, ignores its developments, and occasionally brings charges against it which might be retorted with at least equal effect against his own philosophy. But on the most important point of all, whether Plato did or did not ascribe a separate existence to his Ideas, we could hardly believe a disciple of twenty years’ standing[229] to be mistaken, even if the master had not left on record a decisive testimony to the affirmative side in his _Parmenides_, and one scarcely less decisive in his _Timaeus_.[230] And so far as the controversy reduces itself to this particular issue, Aristotle is entirely right. His most powerful arguments are not, indeed, original, having been anticipated by Plato himself; but as they were left unanswered he had a perfect right to repeat them, and his dialectical skill was great enough to make him independent of their support. The extreme minuteness of his criticism is wearisome to us, who can hardly conceive how another opinion could ever have been held. Yet such was the fascination exercised by Plato’s idealism, that not only was it upheld with considerable acrimony by his immediate followers,[231] but under one form or another it has been revived over and over again, in the long period which has elapsed since its first promulgation, and on every one of these occasions the arguments of Aristotle have been raised up again to meet it, each time with triumphant success. Ockham’s razor, _Entia non sunt sine necessitate multiplicanda_, is borrowed from the _Metaphysics_; Locke’s principal objection to innate ideas closely resembles the sarcastic observation in the last chapter of the _Posterior Analytics_, that, according to