[26] _Principles of Economics_, p. 183. Professor Seligman in the _Q. J. E._ article (_supra_, p. 6, note I) indicates that Pantaleoni expresses a similar thought (_Pure Economics_, London, 1898, p. 127). This idea is elaborated by Professor Georg Simmel, _Philosophie des Geldes, Erster Teil, Kap. 2_. (A translation of this chapter, under the title, "A Chapter in the Philosophy of Value," appears in the _American Journal of Sociology_, vol. v, pp. 577-603. The translation was made from the author's manuscript, before the publication of the book, and does not exactly correspond with the chapter as published by Simmel.) Simmel's contention is that, even for an isolated economy, value arises from exchange, and that exchange is essential to it. Every value is relative to some other value. But to develop this conception, "exchange" is distorted into a variety of meanings. In one place, exchange takes place between an isolated man and his environment. It makes no difference to him whether he is exchanging with other men or with the order of nature (_Phil. des Geldes_, p. 34). But later, exchange is declared to be "a sociological structure _sui generis_" (_ibid._, p. 56). Again, only in the vaguest sort of sense is exchange used in this expression, "_wo wir Liebe um Liebe tauschen_" (_ibid._, p. 33). Yet all these meanings are forced in to fit the exigencies of the argument. The doctrine of cost is brought in, and the exchange is between individual cost and individual utility, and an equality between them is insisted upon, despite the well-known phenomenon of "consumer's surplus." This emphasis on _equality_ in exchanges is stressed especially on p. 31, and economic activity is said to derive its peculiar character from a consideration of these equalities in abstraction.