as one of the universal constituents of Being is Form or Essence (οὐσία), a principle on which I have touched in the preceding section. This principle was advanced by Aristotle in the place of the Platonic ideas which he endeavours to displace and refute. Whether he dealt altogether fairly with the Platonic theory is still a somewhat unsettled question. Aristotle understood Plato to maintain that the ideas existed by themselves apart (χωριστά) from the individual things which were formed after their pattern. That Plato maintained this in literal strictness is not by any means certain. Such, however, was Aristotle's understanding of him. And interpreting him this way, he objected to the doctrine of ideas on the following grounds: First, that such a doctrine is a mere doubling of sensible existences; the ideas are conceived as merely attenuated material objects. Aristotle calls them also αἰσθητά ἀΐδια, that is, everlasting sensibles. Secondly, he says that the ideas not being in things, cannot be the causes of motion or change, and therefore serve no purpose as explanatory of the phenomena of change. Thirdly, that not being in things, they cannot help us to any knowledge of things, and are therefore of no use as explanatory of the phenomenon of knowledge. Fourthly, that they are contradictory, inasmuch as they are represented as the essence of things, and yet as existing separate from things, as if it were possible that the essence of a thing could be separated from the thing of which it was the essence. Fifthly, that the
