On the same principle, Adam Smith considers the value of cattle as rising in the progress of cultivation and improvement, although the value of land, the value of wood, the value of poultry, &c., might rise still higher, and, consequently, a given quantity of cattle might, with regard to some commodities or sets of commodities, have its power of purchasing diminished. But in saying that the value of cattle rises in the progress of cultivation, he means to say, that it rises in relation to a standard, namely, the labour a commodity will command, which represents at different periods the state of the supply of cattle compared with the demand, and, on an average, the elementary costs of their production; and, consequently, much better represents the estimation in which they are held than any commodity or set of commodities. “Labour,” he observes, “it must always be remembered, and not any particular commodity, or set of commodities, is the real measure of the value both of silver and of all other commodities.”[77] Even the author himself has a chapter on the causes of value; and here he finds it absolutely necessary to estimate the causes affecting one commodity as distinct from the causes affecting another; although, according to his previous doctrine, the value of one commodity might be just as powerfully affected by causes operating upon another commodity as by causes operating upon itself: If _a_ and _b_ be compared, the value of _a_ will be equally doubled, whether the elementary cost of _a_ be doubled or the elementary cost of _b_ be diminished one half; and so no doubt it would, if the relation of _a_ to _b_ were alone considered. But what does this prove? not that the value of _a_ is not very differently affected in the two cases, according to the most ordinary, the most useful, and the most correct acceptation of the term value; but that to confine the term value, as the author does, to the mere relation of any one commodity to any other, is to render it pre-eminently futile and useless.