“ The value of every commodity is the product of labour ”
 Karl Marx, Das Kapital (1885). copy citation

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“if we furthermore keep in mind that Adam Smith lumps together labour, so far as it creates value and is an expenditure of labour-power, and labour, so far as it creates use value, i.e., is expended in a useful, appropriate manner — then the entire conception amounts to this: The value of every commodity is the product of labour; hence this is also true of the value of the product of the annual labour or of the value of society’s annual commodity-product. But since all labour resolves itself 1) into necessary labour-time, in which the labourer reproduces merely an equivalent for the capital advanced in the purchase of his labour-power, and 2)” source