realized as use-values, they must be realized as exchange values.
While the single commodity appeared from the standpoint of use-value as something independent, as exchange value it was regarded first of all in its relation to all other commodities. This relation was, however, merely theoretical, imaginary. It becomes real only in the process of exchange. On the other hand, a commodity is an exchange value in so far as a certain quantity of labor-time has been expended on it, and it consequently represents materialized labor-time. But of itself it is only materialized individual labor-time of a particular kind, and not universal labor-time. Therefore, it is not directly an exchange value, but must first become such. First of all, it is an embodiment of universal labor-time only in so far as it represents labor-time applied to a definite useful purpose, i. e., when it represents a use-value. This was the material condition under which alone labor-time contained in commodities was regarded as universal social labor. Thus, while a commodity can become a use-value only after it has been realized as an exchange value, it can, on the other hand, be realized as an exchange value only if it proves to be a use-value in the process of alienation.