Marx introduced the commodity as having a strangely conflicted dual existence as both a use value and an exchange value. He has posed the question of just what is it that is the basis of value – why do we exchange one thing for a specific amount of another thing entirely – what dictates the correct amounts to exchange?
If then we leave out of consideration the use value of commodities, they have only one common property left, that of being products of labour. But even the product of labour itself has undergone a change in our hands. If we make abstraction from its use value, we make abstraction at the same time from the material elements and shapes that make the product a use value; we see in it no longer a table, a house, yarn, or any other useful thing. Its existence as a material thing is put out of sight. Neither can it any longer be regarded as the product of the labour of the joiner, the mason, the spinner, or of any other definite kind of productive labour. Along with the useful qualities of the products themselves, we put out of sight both the useful character of the various kinds of labour embodied in them, and the concrete forms of that labour; there is nothing left but what is common to them all; all are reduced to one and the same sort of labour, human labour in the abstract.
When we exchange two different commodities to the same value we are abstracting them from their inherent use values, that which makes them physically useful objects. They become a different sort of value in exchange, and this is a social value in that it requires an interaction or transaction.
Labour, which produces the physical objects for exchange, is that which creates common social value in commodities. That’s what we’re paying for, and it’s the basis of the value that we’re paying with.
Marx presents the labour contained in the commodity as the standard basis of value across all commodities and, as making all commodities exchangeable with each other reduces all commodities to a general homogenous value, so it reduces all the various types of labour (machine operating, baking, transporting, brick laying, or whatever etc etc…) contained in the commodities to a general labour value. Marx terms this ‘human labour in the abstract’.
He’s making these distinctions so as to indicate how value is created *socially* (ie. it’s never really the preserve of a few, despite social appearances, although it effectively is!)
It consists of the same unsubstantial reality in each, a mere congelation of homogeneous human labour, of labour power expended without regard to the mode of its expenditure. All that these things now tell us is, that human labour power has been expended in their production, that human labour is embodied in them. When looked at as crystals of this social substance, common to them all, they are – Values.
Marx emphasises this generalised labour which creates value as a ‘social substance’.
A use value, or useful article, therefore, has value only because human labour in the abstract has been embodied or materialised in it. How, then, is the magnitude of this value to be measured? Plainly, by the quantity of the value-creating substance, the labour, contained in the article. The quantity of labour, however, is measured by its duration, and labour time in its turn finds its standard in weeks, days, and hours.
This generalised labour will necessarily be measured in time, how long it takes to produce the thing in a given society.
And Marx will later large it up on the heightened significance time, or a capitalist construction of it, takes on under the capitalist mode of production.