Supposing, then, that the exchangeable value of a commodity were defined to be its general power of purchasing, this must refer to the power of purchasing the mass of commodities; but this mass is quite unmanageable, and the power of purchasing it can never be ascertained. With a view, therefore, to its practical application, it would unquestionably be our endeavour to fix upon some object, or set of objects, which would best represent an average of the general mass. Now, of any one object, it cannot for a moment be denied that labour best represents an average of the general mass of productions. There is no commodity considered by society as wealth, for which labour is not, in the first instance, exchanged; there are very few for which it is not exchanged in great quantities: and this can be said of no other object, except labour, and the circulating medium which represents it. It is, at once, the first, the universal, and the most important object given in exchange for all commodities; and if to this we add, that while there is one large class of commodities, such as raw products, which in the progress of society tends to rise as compared with labour, there is another large class of commodities, such as manufactured articles, which at the same time tends to fall; it may not be far from the truth to say, that the portion of the average mass of commodities which a given quantity of labour will command in the same country, during the course of some centuries, may not very essentially vary. Allowing, however, that it would vary, and that labour is an imperfect measure of the general power of purchasing; yet, if some sort of standard more applicable than the mass of commodities be required, and labour appears to be beyond comparison the best representative of this mass, there will be a very powerful reason for adopting labour as the practical measure of value, even among those who may persevere in thinking that the best definition of value in exchange is the general power of purchasing. To those, however, who hold the opinion that the variations in the exchangeable value of a commodity and the variations in its power of purchasing are not identical, and that a commodity increases in exchangeable value only when it will command a _greater value in exchange_, while its power of purchasing may increase merely because it will command a _greater quantity_ of commodities which have confessedly fallen in value, the reasons for adopting labour as the measure of value will be found to increase tenfold in force. There are various ways of describing value in the sense here understood; and the slightest examination of them will show that the labour which a commodity will command can alone be the measure of such value.