In first separating value in exchange from value in use, it may be allowable to distinguish it by the title of the power of purchasing other goods, as Adam Smith has done, though never to interpret this power as the power of purchasing any one sort of goods, as the author has done. But the moment we come to inquire into the variations of the values of commodities at different periods, we must, with any view to precision and utility, draw a marked line of distinction between a variation in the power of purchasing derived from causes affecting the particular purchasing commodities, and the variations in the power of purchasing which may arise from causes operating upon the purchased commodities. We must confine our attention exclusively to the former; and for this purpose refer to some standard which will best enable us to estimate the variations in the elementary costs of production, and in the state of the demand and supply of these commodities, as the best criterion of their varying value, or the varying estimation in which they are held at different periods. On these grounds, Mr. Ricardo, consistently with his peculiar theory, measures the varying values of commodities at different periods by their producing labour. And Adam Smith, consistently with his more just and applicable theory, measures the values of commodities at different periods by the labour which they will command. Among the author’s chapters is one (the seventh) entitled “On the Measure of Value proposed by Mr. Malthus.” In order to prepare himself for the refutations intended, he sums up his principal doctrines respecting value; and as they are here brought into a small compass, I cannot resist the temptation of quoting them in his own words. He says, “It has been shown that the value of labour, like that of any other exchangeable article, is denoted by the quantity of some other commodity for which a definite portion of it will exchange, and must rise or fall as that quantity becomes greater or smaller, these phrases being only different expressions of the same event. Hence, unless labour always exchanges for the same quantity of other things, its value cannot be invariable, and, consequently, the very supposition of its being, at one and the same time, invariable, and capable of measuring the variations of other commodities, involves a contradiction.” “It has also been shown, that to term anything immutable in value, amidst the fluctuations of other things, implies that its value at one time may be compared with its value at another time, without reference to any other commodity, which is absurd, value denoting a relation between two things at the same time; and it has likewise been shown, that in no sense could an object of invariable value be of any peculiar service in the capacity of a measure. “These considerations,” he says, “are quite sufficient to overturn the claims of the proposed measure, as maintained by its advocate.”[78]