=Exchange.=—Hitherto Value has been presented as a relation between Satisfactions and Goods. It remains to say that this subjective valuation becomes objective and explicit in exchange; we have, in fact, a definite expression of this valuation in the thing surrendered in exchange. In other words, we need not measure Value by the subjective satisfaction we should lose in losing the marginal item—we actually do lose the utility we part with in purchasing, and this—generally money—names the value. If exchange were by barter, it would be clear that the exchanger surrendered a utility as well as gained one. Take a shepherd and goatherd bartering successive items of their flocks; the gain and loss of sheep-utility and goat-utility are quite evident—as is also the diminishing marginal utility of the items successively acquired and the increasing marginal utility of the items successively parted with. When money forms the one side of the exchange, it is not essentially different; the motive always is that the thing purchased is considered of greater utility than the money parted with: that is to say, of greater utility than all the things that might, in the circumstances, have been purchased with the money. But, in this case, the money parted with expresses universally the value of the goods bought, and gets the name of Price. Thus Price, in this point of view, is the money expression of Marginal Utility. =Marginal Utility of Money.=—Money, like all other goods, diminishes in utility with increase in the amount of it possessed. But the diminution is much less marked, and never comes near zero, because money is not one commodity, satisfying one want, but is potentially, everything that money can buy, _i.e._, a complex of things satisfying almost the whole complex of wants. Till we have no need for anything which money can buy, the marginal utility of money will not sink to zero. =Demand Price.=—What we have in actual life is not, of course, individual bargains between two persons, where the exchange would be determined by the marginal utility on each side, and Demand Price and Supply Price would be convertible terms. Still what we have, on the one side, is multitudes of people—each with different valuations based on different subjective marginal utilities depending on different circumstances of want and provision—offering Demand Prices. That they are confronted, in the market, with another distinct set of prices brings us to the other side of the total theory of value.