If commodity a equals 1 shilling, and 1 shilling equals 1/x (let us suppose ounces) of silver, and commodity b equals 2 shillings (2/x of silver), then commodity b is of twice the value of commodity a. ‘The value relationship between a and b is expressed by the proportion in which each exchanges against a definite quantity of a third commodity, silver; not against a value relationship.’
Each commodity (whether it is a product intended for unproductive consumption or an article of productive consumption) is equal to ‘the objectification of a particular [amount of] labour time.’ The proportion is which it is exchanged for other commodities (or other commodities are exchanged for it) is equal to the amount of labour time realised in it. A commodity which is equal to one hour’s labour time can be exchanged for any other commodity which is equal to one hour’s labour time. (Assuming, of course, Marx reminds us, that ‘exchange value’ = ‘market value’, that ‘real value’ = price.)
But: ‘[t]he value of a commodity is different from the commodity itself.’ A commodity becomes value only in exchange (whether real or ‘imagined’ [‘vorgestellten’]). The value of a commodity is both its exchangeability ‘in general’ and its ‘specific exchangeability’. ‘It [value] is at once the indicator of the ratio in which the commodity exchanges for others and the indicator of the ratio in which it has already been exchanged for others (materialised labour time) in the process of production.’
‘Value is a commodity’s quantitatively determined exchangeability.’ Different commodities are different in that they possess different properties, they are measured in different units, and are, as such, incommensurable (Marx does not use the term ‘use value’ but that is what he means here), but, as values, they ‘are qualitatively equal and only quantitatively different, hence they can be measured in terms of each other and are mutually replaceable (exchangeable, convertible into each other) in definite quantitative proportions.’
The value of commodities is both their social relationship and their ‘economic quality’. Different kinds of otherwise incommensurable commodities (effectively different use values) are as values mutually exchangeable in given ratios. As a value, a commodity is an ‘equivalent’, and as an equivalent its natural properties disappear. ‘As value it [the commodity] is money.’ But the commodity as a product (‘product’ here is synonymous with what Marx will later call ‘use value’) is distinct from the commodity as a value (and the commodity as a value is distinct from the commodity as a product): the commodity, in one of its guises, is distinct from itself. Thus, since the commodity as a value is qualitatively distinct from itself as a value (and, as a value, is qualitatively similar to other commodities), its value requires a qualitatively distinct existence from itself.
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