Professor Clark develops a theory that the ultimate standard of the value of a good is the “effective social disutility” cost of its acquisition. Thus he presents a theory of distinctively social valuation.[235] But we also find as a part of his doctrines a theory of purely individual valuations. Professor Clark distinguishes clearly between these two, and in fact develops the theory of social from the theory of individual valuation. In drawing the reader’s attention to these doctrines, it will suit our purposes best to emphasize as much as possible the distinction between value in the individual economy and in the social economy. We may, therefore, adopt the device of “Crusoe economics,” and consider the relation of subjective cost to value in the isolated individual economy. In the theory of value, the pursuit of this plan does not involve a waste of time, but on the contrary it is an excellent measure for which there is precedent at some point or other in the writings of nearly all theorists. The plan corresponds to the artifice of the primitive society of hunters and fishers so frequently used and also abused by the classical economists. It is in a peculiar degree a device of what Roscher called the “idealistic method.” We are, of course, now dealing with a problem entirely outside the possible sphere of the “historical method.” We find in the Crusoe economy the prototype, as it were, of many a complex value relation in advanced social conditions, and an appreciation of certain simple and highly generalized principles true of this economy may greatly facilitate our understanding of the difficult subject of cost and value under real conditions. But the strongest reason of all for considering consciously and explicitly the case of Crusoe by himself, is because there are many examples in the literature of value where certain doctrines are laid down ostensibly as universal principles, which are in reality conditioned upon the unconscious assumption of Crusoe conditions. The case of Crusoe should be discussed if only to show what principles are limited to the conditions of his economy.