Unequal volumes of different use-value contain the same quantity of labor-time or the same exchange value. The smaller the volume of a use-value containing a certain quantity of labor-time as compared with other use-values, the greater its specific exchange-value. If we find that certain use-values, such as, e. g., gold, silver, copper and iron, or wheat, rye, barley and oats, form a series of specific exchange values which, though not retaining exactly the same numerical ratio, still retain through widely remote epochs of civilization the same rough proportion of relatively larger and smaller quantities, we may draw the conclusion that the progressive development of the productive powers of society has equally, or approximately so, affected the labor-time necessary for the production of the various commodities.
The exchange value of a commodity is not revealed in its own use-value. But, as the embodiment universal social labor-time, the use-value of one commodity bears a certain ratio to the use-values of other commodities. Thus, the exchange value of one commodity is manifested in the use-values of other commodities. An equivalent is, in fact, the exchange value of one commodity expressed in the use-value of another commodity. If I say, e. g., that one yard of linen is worth two pounds of coffee, then the exchange value of linen is expressed in terms of the use-value of coffee, viz., in a certain quantity of that use-value. This ratio being given, I can express the value of any quantity of linen in coffee. It is clear that the exchange value of one commodity, say linen, is not confined to the ratio of any one commodity, e. g. coffee, as its equivalent. The quantity of universal labor-time which is represented in one yard of linen is at the same time embodied in an endless variety of volumes of use-values of all other commodities. The use-value of any other commodity forms the