THREE:The study of psychology with Plato stands in a fourfold relation to his general theory of the world. The dialectic method, without which Nature would remain unintelligible, is a function of the soul, and constitutes its most essential activity; then soul, as distinguished from body, represents the higher, supersensual element of existence; thirdly, the objective dualism of reality and appearance is reproduced in the subjective dualism of reason and sense; and lastly, soul, as the original spring of movement, mediates between the eternal entities which are unmoved and the material phenomena which are subject to a continual flux. It is very characteristic of Plato that he first strains an antithesis to the utmost and then endeavours to reconcile its extremes by the interposition of one or more intermediate links. So, while assigning this office to soul as a part of the universe, he224 classifies the psychic functions themselves according to a similar principle. On the intellectual side he places true opinion, or what we should now call empirical knowledge, midway between demonstration and sense-perception. Such at least seems to be the result reached in the Theaettus and the Meno. In the Republic a further analysis leads to a somewhat different arrangement. Opinion is placed between knowledge and ignorance; while the possible objects to which it corresponds form a transition from being to not-being. Subsequently mathematical reasoning is distinguished from the higher science which takes cognisance of first principles, and thus serves to connect it with simple opinion; while this again, dealing as it does with material objects, is related to the knowledge of their shadows as the most perfect science is related to mathematics.138It has, until lately, been customary to speak as if all that Aristotle knew about induction was contained in a few scattered passages where it is mentioned under that name in the Analytics. This, no doubt, is true, if by induction we mean simple generalisation. But if we understand by it the philosophy of experimental evidencethe analysis of those means by which, in the absence of direct observation, we decide between two conflicting hypothesesthen the Topics must be pronounced as good a discussion on the subject as was compatible with his general theory of knowledge. For he supposes that there are large classes of phenomena, including, among other things, the whole range of human life, which, not being bound by any fixed order, lie outside the scope of scientific demonstration, although capable of being determined with various degrees of probability; and here also what he has in view is not the discovery of laws, but the construction of definitions. These being a matter of opinion, could always be attacked as well as maintained. Thus the constant conflict and balancing of opposite forces, which we have learned to associate with the sublunary sphere, has its logical representative no less than the kindred ideas of uncertainty and vicissitude. And, in connexion with this side of applied logic, Aristotle has also to consider the requirements of those who took part in the public debates on disputed questions, then very common among educated Athenians, and frequently turning on verbal definitions. Hence, while we find many varieties of reasoning suggested, such as Reasoning by Analogy, Disjunctive Reasoning, Hypothetical Reasoning (though without a generalised expression for all its varieties), and, what is most remarkable, three out of Mills four Experimental Methods,288 we do not find that any interesting or395 useful application is made of them. Even considered as a handbook for debaters, the Topics is not successful. With the practical incompetence of a mere naturalist, Aristotle has supplied heads for arguments in such profusion and such utter carelessness of their relative importance that no memory could sustain the burden, except in the probably rare instances when a lifetime was devoted to their study.
