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physical and moral relations of their images or representations, the phenomena of the physical and moral worlds. Such is the method of Plato when explicitly unfolded.
It results from such a method, that Plato's physics and Plato's logic, or, more strictly, Plato's metaphysics and Plato's dialectics, are the same. His physics is a logico-physics. The words of popular language embodied his whole field of observation. And the logical relations of the words, therefore, constituted, or were commuted with, the physical relations of the things signified by them; because these things were nothing else than the popular meaning of these words. This is sufficiently exemplified in the Platonic doctrine of contraries. This doctrine is, that the ultimate powers
of nature are contraries, and that everything is generated by its contrary. “There is (says Plato) a certain medium between the two contraries. There are two births, or processions—one of this from that, and of that from this. The medium between a greater and a less thing is increase and diminution. The same is the case of what we call mixing, separating, heating, evolving, and all other things without end. For, though it sometimes falls out, that we have not terms to express those changes and mediums, yet experience shows, that by an absolute necessity, things take rise from one another, and pass reciprocally from one to another through a medium." It is manifest, that the two births, or processions, spoken of as subsisting in nature between contraries, are nothing but the logical relations of the meaning of the words greater and less. There are no births, or processions, in nature, corresponding with these relations, constituting a generative medium between the entities greater and less. The whole doctrine is an affair of words. The reasoning is logico-physical. There is nothing real beyond the meaning of the words. The whole of philosophy and science is made nothing more than the development of the meaning of the terms of common language. Plato's philosophy, therefore, like all ancient philosophy, reposes upon mere popular notions. He finds the words, equality, big, little, and other like words, in popular language, and, instead of looking into nature for the real things intended to be signified by these terms, he conceives that there are realities independent of nature corresponding with them. That Plato's supposed higher objects of knowledge, called ideas, are but the popular signification of general terms, is sufficiently manifest from Plato's own theory of the origin of this sort of knowledge. His theory is, that though the knowledge of ideas is acquired in a prior state of existence, yet it is recovered in this world by the ministry of the senses exercised upon individual objects, which recall the ideas by reminiscence. This theory shows, that these ideas are but the general notions formed by every one in the exercise of his faculties upon the objects of nature. In other words, ideas are only the meaning of general terms, which express only relations, and afford no irrespective objects.
So, then, the Idealism of Plato, when sifted to the bottom, is found to be the mere Phenomenalism of the common mind—a lame empiricism. There is no deeper principle underlying it, as is pretended—no knowledge of higher essences remembered from a prior state of existence. A severe logic takes off the veil, and Plato is seen to stand on the common ground of the meagre empiricism of the ancient philosophy. All philosophers necessarily take their departure from the same general experiences, whatever may be pretended to the contrary; and the different results of their specusations will depend upon the difference in the accuracy, the extent, and the completeness of their observations, and legitimate inferences or deductions.
Aristotle appears next in Greek philosophy; he was the very genius of subtlety and of system; and no greater thinker has yet appeared in the family of man. He saw that the Lasis of science and philosophy must, from the very structure of the human mind, be phenomenal. Therefore, he strove to fix logic on a psychological basis. With this view, he proceeded to analyze the senses, and account for the origin of knowledge through sensation. He repudiated the Platonic doctrine of ideas, and contended that the only real existences are individuals, and that generals may be nothing more, so far as the purpose of demonstration is concerned, than terins denoting a property common to an indefinite number of individuals. “ The steady contemplation (says Aristotle, in his Metaphysics), of any individual object under that aspect in which it agrees with other individuals, will recall many similar objects to the mind; the stability of the one will communicate stability to the others, and thus give birth to what are called universals, that is, to general terms, equally applicable to an indefinite number of individuals.” Laying down this doctrine as the basis of his theory of knowing, he at once constructed his logic in accordance with it. Therefore, in his Posterior Analytics, he thus lays down the psychological basis of demonstration : "For the purpose of demonstration, it is not necessary to suppose the existence of general ideas, but only that one general term can be applied with truth, and in the same sense, to many individuals. It is not necessary to suppose that general terms, denoting any class of substances, express anything besides the different particulars to which they apply, any more than the general terms denoting qualities, relations, or actions. One general term stands for a variety of particulars, considered under one and the same aspect; but to suppose that this term requires one substantial archetype or idea, as general as itself, is the hearer's fault; such a supposition not being necessary for the purpose of demonstration."
If we should stop our inquiry here, Aristotle would appear to be a mere Sensationalist; and such is, sometimes, the account of him in history. Plato is represented as a pure Idealist, while Aris
totle is represented as a pure Sensationalist. This is a great mistake ; each is both an Idealist and a Sensationalist-maintaining that human knowledge is derived from both the intellect and the senses. Plato, it is true, considers intellect exercised upon ideas, the sole source of science; yet he ascribed some degree of knowing to the senses. Aristotle ascribed much more importance to sense, but yet made both intellect and sense the conjunct principle of science. He rejected the Platonic doctrine of ideas, but, as we shall see, did not advance as far beyond it as the quotations from his writings which we have given above seem at first to indicate.
It behooves us here to inquire, what is the Platonic doctrine of ideas? The word idea, since the time of Des Cartes, has been employed to denote the objects of our consciousness in general; and, since the time of Gassendi and Condillac, whose school analyzed our highest faculties into our lowest, the word has been used to denote the objects of our senses in general. We have already seen that Plato used the word in a far different sense from either of these. He employed it to express the real forms of the intelligible world in lofty contrast with the images of the sensible. It was in this Platonic sense that Aristotle rejected the doctrine of ideas. “ Plato (says Aristotle), came to the doctrine of ideas, because he was convinced of the truth of the Heraclitic view, which regards the sensible world as a ceaseless flowing and changing. His conclusion from this was, that if there be a science of anything, there must be, besides the sensible, other substances which have permanence; for there can be no science of the fleeting.” In Plato's view, science demanded the reality of ideas as permanent existences, independent of sensible phenomena. Aristotle maintained that there is no proof of the independent reality of ideas; and that, at any rate, the doctrine furnishes no ground for the explanation of being. That Plato, in order to make science possible, had arbitrarily posited certain substances independent of the sensible and uninfluenced by changes—but that only individual things are offered to us objectively. Therefore, that it is the individual which is conceived as universal, or perhaps, that the universal is perceived in the individual; and that this conception or perception is the objectified idea of Plato.
The doctrine, that the universal can be perceived in the individual, which was, perhaps, the opinion of Aristotle, when sifted to the bottom, is simply this. The products of the understanding or generalising faculty have both a general and an individual element, constituting two opposite logical poles. The simplest operation of this faculty is to compare together the points of resemblance between objects, and reduce them to one in the synthesis of thought. The product of this process is a concept. A concept being the result of a comparison, necessarily expresses a relation;
it therefore affords no absolute or irrespective object of knowledge. In this aspect, it is general ; but it can be realized in consciousness, by applying it, as the term of relation, to one or more of the objects which agree in the point or points of resemblance which it expresses. In this aspect, it is individnal. A concept, therefore, is a synthesis of the universal, and the individual expressed in a term of relation. And it is the obscure consciousness of this conjunction of the universal and the individual in the products of the understanding, which has led men to assert the existence of universals in nature. It is but the common error in philosophy of commuting the subjective for the objective. This criticism, we believe, has never been made before. It seems to us to furnish a clue to the fundamental errors in philosophy.
From the criticism of Plato's doctrine of ideas, arose Aristotle's doctrine of matter and form. Aristotle enumerates four metaphysical causes or principles; matter, form, moving cause, and end. But these four can be resolved into the fundamental antithesis of matter and form. Matter and form, therefore, are, according to the Aristotelic doctrine, the only things which cannot be resolved into each other. Matter, according to Aristotle, is capable of the widest diversity of forms, but is itself without determinate form: it is everything in possibility, but nothing in actuality._Matter is thus a far more positive thing with Aristotle than with Plato, who treated it as a shadow. We must guard against the supposition, that Aristotle means by form what we mean by shape. The Aristotelic form is an activity which becomes actualized, through matter, in individual objects.
Aristotle's theory of knowledge corresponds with his theory of forms. As, according to his metaphysical doctrine, forms or universals exist not apart froin, but in individual objects, he made, as we have said before, both intellect and sense important faculties in science. He held that there is an a priori knowledge paramount to, but not exclusive of, the a posteriori. That, though universals are known through the intellect and implicitly contain particulars, yet we may remain ignorant of particulars until they are realized through the senses. Therefore, that intellect and sense combine in framing the fabric of science. Accordingly Aristotle's method is two-fold, deductive and inductive; the first allied with intellect and forms, or universals; the second, with sense and individuals. In conformity with this doctrine, Aristotle seems to have considered syllogism proper, or deduction, no less ampliative than induction; that deduction did, in some way, assure us, or fortify our assurance, of real truth.
Though Aristotle turned the mind to outward contemplation, he did not perceive the full import of observation, nor the full scope of induction. He still, in conformity with ancient thinking, made universals the paramount element of science, and intellect
the paramount principle. It is true, that his doctrine of universals differed metaphysically from that of Plato; but logically it came to very much the same result in its influence upon method. There are, according to Aristotle's theory of knowledge, certain universal principles existing in the mind, rather as native generalities than as mere necessities of so thinking, which furnish the propositions for syllogism; therefore syllogism or deduction is not dependent for these on induction. Syllogism is thus the paramount process, and induction an inferior process, which may be used as corroborative of deduction; and may be especially used by such minds as cannot realize a priori universals, but may perceive them in individuals. Aristotle directed all his energies towards constructing a system of deductive logic. And he assumed that the notions contained in the language of his day were sufficiently accurate for philosophy and science. Some of the profoundest distinctions of his philosophy are to be found in the very structure of the Greek language. The distinction, for instance, of power into active and passive which is said to have been established by Aristotle, and was adopted by Locke and by Leibnitz, is found in the very fabric of the Greek language, which possesses two sets of potential adjectives, the one for active and the other for passive power. Those significant of active power are denoted by the termination ixos, and those of passive, by that of cos.* Though, therefore, Aristotle extricated logic from the metaphysical errors of Plato, he fell into
error, but not so gross, under a different name; for Plato's ideas and Aristotle's forms are, at bottom, but the common notions expressed by general terms. In his investigations, Aristotle generally starts out by saying: “It is said so and so; and his procedure is ratiocination founded upon common notions. The doctrine of contraries, too, as was the case with Plato, is a sophistry by which he deceived himself. And in his reasonings, his doctrine of forms, sometimes, unconsciously to himself, slips into Plato's doctrine of ideas. And we doubt whether Aristotle's estimate of induction, as a method of material inquiry, was higher than that of the ancient Greek skeptics as recorded by Sextus Empiricus in these words: “ Induction is the conclusion of the universal from individual things. But this induction can only be correct in as far as all the individual things agree with the universal. This universality must, therefore, be verified before its induction can be made: a single case to the contrary would destroy the truth of the induction.” The weakness of induction, as indicated by this criticism of the skeptics, was overrated by Aristotle; as his whole logic seems to assume, in the very subordinate place given to
* Ποιητικον signifies that which can make, and ποιησον, that which can be made; XIVnTixov, that which can move, and mountov, that which can be moved.