Part Six — Wages Chapters 19–22. The wage-form as the mystification of the value of labour-power, time-wages, piece-wages, and national differences in wages.

Part Six returns to the wage, the form in which the whole relation of exploitation presents itself on the surface of society — and conceals itself there. Chapter 19 is the conceptual heart: it shows that "the value of labour" is an irrational expression, that what is actually sold is labour-power, and that the wage-form systematically hides the division of the working day into paid and unpaid labour. Chapters 20 and 21 examine the two principal forms the wage takes, time-wages and piece-wages, and how each is used to intensify exploitation; Chapter 22 turns to national differences in wages. The Part is short, and its load lies almost entirely in Chapter 19, because the wage-form is the mystification on which "all the notions of justice held by both the worker and the capitalist" are built.

On the surface, the wage looks like the price of labour — so much money for so much labour, with a "value of labour" oscillating around a natural price. Marx shows the phrase is incoherent. Value is measured by labour-time, so "the value of labour" would mean the labour-time contained in a quantity of labour, an empty tautology; and labour has no independent existence to be sold before it is performed. What confronts the money-owner is not labour but the worker, and what is sold is labour-power.

Labour is the substance, and the immanent measure of value, but it has no value itself. In the expression ‘value of labour’, the concept of value is not only completely extinguished, but inverted, so that it becomes its contrary. It is an expression as imaginary as the value of the earth. These imaginary expressions arise, nevertheless, from the relations of production themselves. They are categories for the forms of appearance of essential relations.

Marx, Capital I, page 677.