In its most definite form, the theory asserts that the value of an economic good is determined by, and precisely accords with, the marginal utility of the good to society, considered as a unitary organism. Professor Clark, as is well known, makes use of the analysis of diminishing utility in an individual's consumption of goods in much the same fashion that Jevons does, but while Jevons makes this simply a step in the analysis of market ratios of exchanges, Professor Clark treats it as analogical, representing _in parvo_ what society does, as an organic whole, on a bigger scale.[4] The precise relation of social value to social marginal utility is variously stated by the writers named: for Professor Clark, value is the _measure_ of effective, or marginal, utility;[5] for Professor Seligman, social value is the _expression_ of social marginal utility;[6] for Professors Ross, Merriam, and Kinley, value _is_ that social marginal utility itself.[7] These statements are more different in words than in ideas, though some significance is to be attached to Professor Seligman's formulation, as will later appear. This conception is a bold one. It has, moreover, never been adequately developed or criticized. Its friends have found it a convenient and useful working hypothesis, and Professor Clark, especially, has built a great system upon it, but, with the exception of an article in the _Yale Review_ of 1892,[8] has made no serious efforts, either to make clear its full meaning, or to vindicate it--except that, of course, his whole system may be considered such a vindication. Professor Seligman, in an article in the _Quarterly Journal of Economics_, vol. XV, and also in his _Principles of Economics_, has espoused the conception, and has shown how, assuming its truth, a great many antagonistic theories may be harmonized; but he, also, has failed to treat it with that detail which full demonstration requires. In particular, he has omitted a treatment of the problem of the relation between the value of a good for the individual and for society, and the relation between individual and social marginal utility.[9] The most searching investigation of the theory has come from unfriendly critics, among whom may be especially named Professor H. J. Davenport, and Professor J. Schumpeter of Vienna.[10]