Use values cannot confront each other as commodities, unless the useful labour embodied in them is qualitatively different in each of them.
 Karl Marx, Das Kapital (1867). copy citation

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Author Karl Marx
Source Das Kapital
Topic value commodity
Date 1867
Language English
Reference
Note Translated by Samuel Moore and Edward Aveling
Weblink https://www.marxists.org/archive/marx/works/download/pdf/Capital-Volume-...

Context

“Only such products can become commodities with regard to each other, as result from different kinds of labour, each kind being carried on independently and for the account of private individuals. To resume, then: In the use value of each commodity there is contained useful labour, i.e., productive activity of a definite kind and exercised with a definite aim. Use values cannot confront each other as commodities, unless the useful labour embodied in them is qualitatively different in each of them. In a community, the produce of which in general takes the form of commodities, i.e., in a community of commodity producers, this qualitative difference between the useful forms of labour that are carried on independently by individual producers, each on their own account, develops into a complex system, a social division of labour.” source