"To the man, therefore, who has in fullest measure this knowledge of universals, all knowledge must lie to hand; for in a way he knows all that underlies them. Yet in a sense these universals are what men find hardest to apprehend, because they stand at the furthest extremity from the perceptions of sense."
"Yet if anything exist which is eternal, immovable, freed from gross matter, the contemplative science alone can apprehend this. Physical science certainly cannot, for physics is of that which is ever in flux; nor can mathematical science apprehend it; we must look to a mode of science prior to and higher than both. The objects of physics are neither unchangeable nor free from matter; the objects of mathematics are indeed unchangeable, but we can hardly say they are free from matter; they have certainly relations with matter. But the first and highest science has to do with that which is unmoved and apart from matter; its function is with the eternal first causes of things. There are therefore three modes of theoretical inquiry: the science of physics, the science of mathematics, the science of God. For it is clear that if the divine is anywhere, it must be in that form of existence I have spoken of (_i.e._ in first causes). . . . If, therefore, there be { 181} any form of existence immovable, this we must regard as prior, and the philosophy of this we must consider the first philosophy, universal for the same reason that it is first. It deals with existence as such, inquiring what it is and what are its attributes as pure existence."
This is somewhat more technical than the language of Plato, but if we compare it with what was said above (p. 142) we shall find an essential identity. Yet Aristotle frequently impugns Plato's doctrine of ideas, sometimes on the lines already [322] taken by Plato himself (above, p. 158), sometimes in other ways. Thus (_Met_. Z. 15, 16) he says: "That which is _one_ cannot be in many places at one time, but that which is common or general is in many places at one time. Hence it follows that no universal exists apart from the individual things. But those who hold the doctrine of ideas, on one side are right, viz. in maintaining their separate existence, if they are to be substances or existences at all. On the other side they are wrong, because by the idea or form which they maintain to be separate they mean the one attribute predicable of many things. The reason why they do this is because they cannot indicate what these supposed imperishable essences are, apart from the individual substances which are the objects of perception. The result is that they simply represent them under the same forms as { 182} those of the perishable objects of sensation which are familiar to our senses, with the addition of a phrase--_i.e._ they say 'man as such,' 'horse as such,' or 'the absolute man,' 'the absolute horse.'"