The real assumption of the economist therefore is, as I think, simply the existence of a certain industrial organisation, which has a real existence as much as an army or a church; and there is no reason why his description should not be as accurate as the complexity of the facts allows. He is giving us the anatomy of society considered as a huge mechanism for producing and distributing wealth, and he makes an abstraction only in the sense that he is considering one set of facts at a time. The military writer would describe the constitution of an army without going into the psychological or political conditions which are of course implied, and without considering the soldiers in any other relations than those implied in their military services. In the same way, the economist describes the army of industry, and classifies its constituent parts. In order to explain their mutual relations, he has to make certain further assumptions, of which it would be rash to attempt a precise summary. He assumes as a fact, what has of course always been known, that scarcity implies dearness and plenty cheapness; that commodities flow to the markets where they will fetch the highest prices; that there is a certain gravitation towards equalisation of profits among capitalists, and of wages among labourers; so that capital or labour will flow towards the employments in which they will secure the highest reward. He endeavours to give the greatest accuracy to such formulæ, of which nobody, so far as I know, denies a certain approximate truth. So long as they hold good, his inferences, if logically drawn, will also hold good. They take for granted certain psychological facts, such as are implied in all statements about human nature. But the economist, as an economist, is content to take them for granted without investigating the ultimate psychological laws upon which they depend. Those laws, or rather their results, are a part of his primary data, although he may go so far into psychological problems as to try to state them more accurately. The selfishness or unselfishness of the economic man has to be considered by the psychologist or by the moralist; but the economist has only to consider their conclusions so far as they affect the facts. So long as it is true, for example, that scarcity causes dearness, that profits attract capital, that demand and supply tend to equalise each other, and so forth, his reasonings are justified; and the further questions of the ethical and psychological implications of these facts must be treated by a different science. The question of the play of economic forces thus generally reduces itself to a problem which may be thus stated: What are the conditions of industrial equilibrium? How must prices, rates of wages, and profit be related in order that the various classes concerned may receive such proportions of produce as are compatible with the maintenance of the existing system of organisation? If any