Footnote

Marx discovered and wrote in volume 3 of Capital that the prices of particular commodities cannot be equal to their labor values when some are produced using more machinery per worker than others. Instead, the prices will deviate from the labor values, being somewhat higher when more machinery is used than the average production process, and less when less than average machinery is used. This is something of a problem for the Marxist theory of exploitation: could the labor value of labor deviate from the price of labor, the wage, in ways that would eliminate surplus-value and exploitation? While no-one has produced an example in which this happens (to the best of my knowledge), the possibility undercuts the surplus value theory, so, in the context of a reasonable dialog, Marxists need an answer to it.

Friedrich Engels (writing in the preface to volume 3 of Capital ) felt the answer would go as follows: exploitation, profits, and the rate of profit are determined by the surplus-value in production in the economy as a whole. If production is not subdivided into different commodities, then there are no differences in machinery per worker to cause problems. The rate of profits determined in this way can then be used to adjust the labor-values to get the long-period price of each commodity, depending on the machinery per worker used.

Not all Marxists regard this answer as quite sufficient, and no committed critic of Marxism accepts it, so far as I know. It may be that some additional assumptions are needed to clarify the theory of surplus value, and some Marxists and non-Marxist economists who accept most of the Marxist approach have discussed what they might be. Marxism, like Neoclassical Economics, has some unresolved basic issues, and different people will disagree as to whether the unresolved issues are fatal in one case or in the other or in both cases.