Value

Value is the labour-time required to produce a Use Value. Value is measured and expressed as an amount of Labour-time, whereas Exchange Value can only be expressed as a quantity of some other Use Value.  A Use Value that is not the product of human labour – for example air – does not have Value. Use Values do not have to be commodities to have Value. A primitive Community that produces Use Values for their own consumption, does not produce commodities, but does produce Use Values that have Value, because they have required human labour to produce.  The Value for this community of producing 20 yards of linen is expressed in the fact that, it has had to forgo the coat it could have produced instead.  How much Value a society places on a particular Use Value can be gauged by the proportion of social labour-time it devotes to its production.

The orthodox economics equivalent of Value is Opportunity Cost in Production

As Marx says in Capital, Value is both logically and historically prior to Exchange Value. All Use Values possess Value prior to becoming commodities, and prior to having Exchange Value. Exchange Value can only arise when all of these Values are brought into a social relation one with another through Exchange.