“ … [sc. Marx] declares that labor … means the ‘expenditure of simple [unskilled] labor power, an average of which is possessed in his physical organism by every ordinary man, without special cultivation"; or in other words ‘simple average labor’ (I, 51, and also previously in I, 46).This is correct: Marx faces the problem of reducing all heterogeneous human labour to a homogeneous abstract socially necessary labour time unit, but does not properly explain how this happens.
‘Skilled labor,’ he continues, ‘counts only as concentrated or rather multiplied unskilled labor, so that a small quantity of skilled labor is equal to a larger quantity of unskilled labor. That this reduction is constantly made experience shows. A commodity may be the product of the most highly skilled labor, but its value makes it equal to the product of unskilled labor, and represents therefore only a definite quantity of unskilled labor. The different proportions in which different kinds of labor are reduced to unskilled labor as their unit of measure are fixed by a social process beyond the control of the producers, and therefore seem given to them by tradition.’
This explanation may really sound quite plausible to the hasty reader, but if we look at it coolly and soberly we get quite a different impression.
The fact with which we have to deal is that the product of a day’s or an hour’s skilled labor is more valuable than the product of a day's or an hour's unskilled labor; that, for instance, the day's product of a sculptor is equal to the five days’ product of a stone-breaker. Now Marx tells us that things made equal to each other in exchange must contain ‘a common factor of the same amount,’ and this common factor must be labor and working time. Does he mean labor in general? Marx's first statements up to page 45 would lead us to suppose so; but it is evident that something is wrong, for the labor of five days is obviously not ‘the same amount’ as the labor of one day. Therefore Marx, in the case before us, is no longer speaking of labor as such but of unskilled labor. The common factor must therefore be the possession of an equal amount of labor of a particular kind, namely, unskilled labor.
If we look at this dispassionately, however, it fits still worse, for in sculpture there is no ‘unskilled labor’ at all embodied, much less therefore unskilled labor equal to the amount in the five days’ labor of the stone-breaker. The plain truth is that the two products embody different kinds of labor in different amounts, and every unprejudiced person will admit that this means a state of things exactly contrary to the conditions which Marx demands and must affirm, namely, that they embody labor of the same kind and of the same amount!.” (Böhm-Bawerk 1949 : 81–82).
First, Marx suggests that the reduction of skilled labour to a simple unit of abstract labour can be conducted in a physical or scientific manner by examining the “expenditure of human brains, nerves, and muscles.” But it is utterly unclear how one can aggregate the labour of a human surgeon or solicitor and that of brick-layer, and Marx quickly passes over the problem.
But then Marx states that:
“Experience shows that this reduction is constantly being made. A commodity may be the product of the most skilled labour, but its value, by equating it to the product of simple unskilled labour, represents a definite quantity of the latter labour alone. The different proportions in which different sorts of labour are reduced to unskilled labour as their standard, are established by a social process that goes on behind the backs of the producers, and, consequently, appear to be fixed by custom.” (Marx 1906: 51–52).Note that such an argument only works if commodities tend to exchange at their true labour values.
But since Marx admits that most commodities do not even exchange for their true labour values by volume 3 of Capital, this argument does not work. The whole thing falls apart; it collapses like a house of cards. Marx is left with the need for a physical or scientific manner of aggregating all heterogeneous types of human labour by reducing all labour to a homogeneous unit of simple labour, but this is an insolvable aggregation problem.
In short, this is a major reason why the whole concept of homogeneous socially necessary labour time in volume 1 of Capital cannot even get off the ground.
Böhm-Bawerk, Eugen von. 1949 . “Karl Marx and the Close of His System,” in Paul. M. Sweezy (ed.), Karl Marx and the Close of His System and Böhm-Bawerk’s Criticism of Marx. August M. Kelley, New York. 3–120.
Marx, Karl. 1906. Capital. A Critique of Political Economy (vol. 1; rev. trans. by Ernest Untermann from 4th German edn.). The Modern Library, New York.