In this section, we will show that complex and simple labour are both abstract labour, and that the reduction of complex to simple labour thus presupposes the independent and prior reduction of concrete to abstract labour.
Imagine two kinds of weaving-labour, simple and complex, and assume one can somehow determine that each hour of the complex counts as equal to 2 hours of the simple. Suppose that 10 hours of simple weaving-labour are extracted, and 3 hours of the complex. Then, by reduction, the amount of simple weaving-labour = 1 × 10 + 2 × 3 = 16.
Similarly, assume that one can somehow determine that each hour of complex tailoring-labour counts as equal to 4 hours of simple tailoring-labour, and that 12 hours of the simple and 5 hours of the complex are extracted. Then, by reduction, the amount of simple tailoring-labour = 1 × 12 + 4 × 5 = 32.
Now, how much total labour is done? We can’t add 16 simple weaving-hours to 32 simple tailoring-hours – they are concretely different. We can’t say that twice as much simple tailoring-labour is done as simple weaving-labour – again, we’d be comparing apples and oranges. Nor can we say that the complex tailoring-labour is twice as complex as the complex weaving-labour, or even that an hour of the simple weavers is equal to an hour of the simple tailors.
The only way to make any quantitative comparison across industries is if we are already talking about abstract labour. If it is the case, for instance, that 1 hour of simple-weaving labour and 1 hour of simple tailoring-labour each equal 1 hour of simple abstract labour, then the weavers do 16 hours of abstract labour, half as much as the 32 hours extracted from the tailors, the total labour extracted is 48 hours, and so on.
This example shows clearly that the concrete/abstract question is separate from the complex/simple question. Even after one knows the amounts of simple weaving-labour and simple tailoring-labour extracted, one doesn’t have a clue as to the amounts of simple general labour, ‘labour-as-such’, extracted – unless the weaving and tailoring have both been already reduced from concrete to abstract.
The example also shows that concrete/abstract is ‘prior to’ complex/simple in the sense that one needs the former reduction to say anything about the latter across different kinds of concrete labour, but the converse is not true. When we refer to simple and complex labour, we do not refer to simple weaving-labour or complex tailoring-labour, and so on, but to simple and complex labour-as-such. The commensuration of labours that produce different use-values is already presupposed. When we computed the amounts of abstract labour extracted, however, although we needed to presume a knowledge of skill differences within each industry, we did not first have to reduce complex labour-as-such to simple labour-as-such.
Complex labour can be compared to, and thus reduced to a multiple of, simple labour, only because they lack any qualitative difference, i.e., only because both are abstract labour. As Marx ([Capital, Vol. 1, Chap. 1]) noted, ‘the magnitudes of different things only become comparable in quantitative terms when they have been reduced to the same unit’.