If society must expend on the average much labour in order to produce any article, the price of that article is high; if on the average little labour is required, the price of the article is low. Assuming average efficiency of manufacture (that is to say, when the machinery and tools employed are neither the very best nor the very worst), the amount of social labour requisite for the production of a commodity is termed the value of that commodity. We see that price depends upon value. In actual fact, price is sometimes higher than value and sometimes lower, but for simplicity we may here assume that they are one and the same.
We must now recall what we said concerning the hiring of wage workers. The hiring of a worker is the sale of a peculiar commodity, the name of which is “labour power.” As soon as labour power has become a commodity, what applies to other commodities applies to labour power. When the capitalist hires the worker, the former pays the latter the price of his labour power (or, to speak simply, the value of his labour power). By what is this value determined? We have seen that the value of all commodities is determined by the quantity of labour expended in producing them. The same thing applies to labour power.
What, however, do we mean by the production of labour power? Labour power is not indeed produced in a factory, like cloth, blacking, or machinery. How then are we to explain it? We have merely to look at contemporary life under capitalism in order to understand with what we are concerned. Let us suppose that the workers have just finished their day’s work. They are tired out, all their vital energy has been used up, they cannot work any more. Their labour power is practically exhausted. What is needed to restore it? Food, rest, sleep, recuperation, and therewith strength will be restored. Then will reappear the capacity for work; then, once more, they will have labour power. This means that food, clothing, and shelter — in a word, the necessaries that the worker consumes — effect the production of his labour power. Additional elements have to be considered, such as expenditure upon training when skilled workers are needed, and so on.