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.'"
Aristotle here makes a point against Plato and his school, inasmuch as, starting from the assumption that of the world of sense there could be no knowledge, no apprehension fixed or certain, and setting over against this a world of general forms which were fixed and certain, they had nothing with which to fill this second supposed world except the data of sense as found in individuals. Plato's mistake was in confusing the mere 'this,' which is the conceived starting-point of any sensation, but which, like a mathematical point, has nothing which can be said about it, with individual objects as they exist and are known in all the manifold and, in fact, infinite relations of reality. The bare subject 'this' presents at the one extreme the same emptiness, the same mere possibility of knowledge, which is presented at the other by the bare predicate 'is.' But Plato, having an objection to the former, as representing to him the merely physical and therefore the passing and unreal, clothes it for the nonce in the various attributes which are ordinarily associated with it when we say, 'this man,' 'this horse,' only to strip them off successively as data of sensation, and so at last get, by an illusory process of {183} abstraction and generalisation, to the ultimate generality of being, which is the mere 'is' of bare predication converted into a supposed eternal substance.
Aristotle was as convinced as Plato that there must be some fixed and immovable object or reality corresponding to true and certain knowledge, but with his scientific instincts he was not content to have it left in a condition of emptiness, attractive enough to the more emotional and imaginative Plato. And hence we have elsewhere quite as strong and definite statements as those quoted above about universals [316] (p. 180), to the effect that existence is in the fullest and most real sense to be predicated of individual things, and that only in a secondary sense can existence be predicated of universals, in virtue of their being found in individual things. Moreover, among universals the species, he maintains, has more of existence in it than the genus, because it is nearer to the individual or primary existence. For if you predicate of an individual thing of what species it is, you supply a statement more full of information and more closely connected with the thing than if you predicate to what genus it belongs; for example, if asked, "What is this?" and you answer, "A man," you give more information than if you say, "A living creature."
How did Aristotle reconcile these two points of {184} view, the one, in which he conceives thought as starting from first causes, the most universal objects of knowledge, and descending to particulars; the other, in which thought starts from the individual objects, and predicates of them by apprehension of their properties? The antithesis is no accidental one; on the contrary, it is the governing idea of his Logic, with its ascending process or Induction, and its descending process or Syllogism. Was thought a mere process in an unmeaning circle, the 'upward and downward way' of Plato?
As to this we may answer first that while formally Aristotle displays much the same 'dualism' or unreconciled separation of the 'thing' and the 'idea' as Plato, his practical sense and his scientific instincts led him to occupy himself largely not with either the empty 'thing' or the equally empty 'idea,' but with the true individuals, which are at the same time the true universals, namely, real objects as known, having, so far as they are known, certain forms or categories under which you can class them, having, so far as they are not yet fully known, a certain raw material for further inquiry through observation. In this way Thought and Matter, instead of being in eternal and irreconcilable antagonism as the Real and the Unreal, become parts of the same reality, the first summing up the knowledge of things already attained, the second symbolising the infinite {185} [317] possibilities of further ascertainment. And thus the word 'Matter' is applied by Aristotle to the highest genus, as the relatively indefinite compared with the more fully defined species included under it; it is also applied by him to the individual object, in so far as that object contains qualities not yet fully brought into predication.
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And second, we observe that Aristotle introduced a new conception which to his view established a vital relation between the universal and the individual. This conception he formulated in the correlatives, Potentiality and Actuality. With these he closely connected the idea of Final Cause. The three to Aristotle constituted a single reality; they are organically correlative. In a living creature we find a number of members or organs all closely interdependent and mutually conditioning each other. Each has its separate function, yet none of them can perform its particular function well unless all the others are performing theirs well, and the effect of the right performance of function by each is to enable the others also to perform theirs. The total result of all these mutually related functions is Life; this is their End or Final Cause, which does not exist apart from them, but is constituted at every moment by them. This Life is at the same time the condition on which alone each and every one of the functions constituting it can be performed. Thus {186} life in an organism is at once the end and the middle and the beginning; it is the cause final, the cause formal, the cause efficient. Life then is an Entelechy, as Aristotle calls it, by which he means the realisation in unity of the total activities exhibited in the members of the living organism.
In such an existence every part is at once a potentiality and an actuality, and so also is the whole. We can begin anywhere and travel out from that point to the whole; we can take the whole and find in it all the parts.
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