As seen above, Plato was the first great economic thinker of Greece.[68] Plato, however, was primarily interested in neither economics nor politics, but in moral idealism. He is pre-eminent, even among the Socratics, for this. All his economic thought is a direct outgrowth of it, and is shot through with its influence. Yet, despite this fact, he exhibits considerable insight into some of the basal principles of economics,[69] and his entire _Republic_ is founded upon an essentially economic theory of society. He traces its origin to mutual need,[70] and makes little of the innate social impulse, so prominent in Aristotle’s analysis.[71] He is the predecessor of Aristotle, however, in opposing the social contract doctrine of the Sophists with its interpretation of law as mere convention, by a natural theory of social origins. To his thought, the very foundations of society are established in eternal justice. They are not the result of mere convention, nor altogether the work of inspired lawgivers, but a complex product of natural and artificial elements.[72] VALUE Strictly speaking, Plato’s contribution to a theory of economic value and a definition of wealth is practically nil. In his discussion of just price, he merely hints at the fact of exchange value. He implies that, since goods exchange according to definite proportions, they should have a common quality capable of measurement, and that just price corresponds to this.[73] He offers no suggestion as to the nature of this quality, except that, in stating that “the artisan knows what the value of his product is,” he seems to be thinking of labor, or cost of production, as the chief element in value.[74] In other passages, he insists on the doctrine taught previously by Democritus,[75] and later by Xenophon and other philosophers, that so-called goods depend for their value upon the ability of the possessor to use them rightly.[76] This idea is represented in modern thought especially by Ruskin.[77] The theory is, of course, true of absolute value, and, in a sense, even of economic value, in that “all exchangeableness of a commodity depends upon the sum of capacity for its use.”[78] It cannot be made a criterion of economic value, though the allied idea, implied by Plato and urged by Ruskin, that the innate quality of the thing, its capacity for good or harm, is a real element in economic value, is being recognized today. This is evident in the increasing hostility toward such so-called commodities as opium and intoxicating liquors. Since we have begun to define political economy in terms of human life rather than in terms of property, Ruskin’s definition of wealth is more acceptable: “the things which the nature of humanity has rendered in all ages, and must render in all ages to come ... the objects of legitimate desire.”[79] WEALTH