This is, I think, what we mean by "money." It is the social expression of value separated from the concrete particularity of any use value. .
With this emergence of money as the social expression of value, money stands, in opposition to commodities, as the abstract always stands in opposition to the particular. We will see value in two forms: as particular commodities, and as money. It is crucial to recognize that this development is latent in the commodity form itself. Insofar as commodity relations are well developed, so that exchange of products is common and people are forced willy nilly to consider the value of products separately from their use values, the money form of value will also be present. There is no reason to think of the commodity form emerging historically before the money form. To the degree that we see the first, we will see the second, or reasons why the emergence of money is suppressed in the concrete situation. What we see historically are very different stages of development of commodity relations, corresponding to different degrees of development of social production and to different forms of money. .
These differences in levels of development may give the illusion of an historical emergence of money separate from, and subsequent to, the emergence of commodities. But in such cases what is at issue is the particular form of money, or the way in which value manifests itself in the particular society. Even transactions which are apparently barter transactions, in that the equivalents exchanged are both concrete commodities, may best be analyzed as degenerate monetary transactions, in which the parties estimate the abstract value of their respective products, and finding them equal, or nearly equal, are able to avoid transferring money itself. .
Marx regards value, the general power of exchangeability that resides in commodities, as an expression of the labor expended in the production of the commodities.