accurate to speak of the price of money in terms of commodities, or of a composite of commodities, as to speak of prices of commodities in terms of money. That is to say, the economist gives himself little concern, in his quasi-mathematical study, as to the ultimate nature of the social forces that manifest themselves in the market. A host of forces lie back of demand, but the economist puts the phenomena of demand into a curve which is the function of two variables, one a quantity of money, and the other a quantity of goods. Lying back of these quantities of goods and money, and giving meaning to the curve, are the more fundamental quantities, the value of the goods and the value of the money. Further than this, for the purposes of his quasi-mathematical, pure theory, the pure economist has no real occasion to go--in proof of which it need be remarked simply that the most divergent theories as to the nature of value, none of them adequate if the theory set forth in this book be true, have not prevented the development of a vast, highly organized, and immensely useful body of price doctrine, shared by economists of many schools. If only the economist have a quantitative value concept, he can do wonders. And, if the question be regarding relations between factors where the question of the value of money may be ignored, he may often safely abstract from the idea of value, and speak simply of money quantities, and relative changes in these money quantities. Such is, indeed, Professor Marshall's procedure in a large part of his great work. Professor Davenport's contention that, from the standpoint of the entrepreneur, the whole thing may be looked at in pecuniary terms, is true of many problems. Cost for the entrepreneur is simply a money matter. And while, for the more fundamental analysis, we of course must insist that a host of psychic forces determine what those money costs shall be, our analysis will justify the contention that it is impossible to treat them in any but price terms, in a precise and quantitative manner. They are too complex. Certainly labor-pain and abstinence, looked on as abstract individual feeling-magnitudes, will not explain the supply-prices of labor and capital, any more than individual "utilities" will explain demand-schedules. And we may add that the terms "social cost" and "social utility" can, in our scheme, get no meaning that will make them useful. The social value concept seems to us absolutely essential for the validation of the whole procedure of the price analysis, and to be implied in every step in it, but the only meaning we can find for the concept of social marginal utility would be one which would make it identical with social value; and against that there are two objections: first, it would be superfluous, and second, it would be misleading. "Social utility" can get only a vague, analogical meaning in our scheme. Instead of explaining social value, it would itself present a problem.[207] A measure