Das Kapital

Part IV begins here with Marx's second major method by which capitalists expand surplus-value: relative surplus-value. Absolute surplus-value, covered in Part III, means extending the working day. But there are physical and political limits to that extension — Chapter 10 showed the bitter struggle required just to maintain existing hours. Relative surplus-value is the alternative: not lengthening the working day but shifting the internal division of it. If necessary labour time — the portion during which workers reproduce the value of their wages — can be shortened, surplus labour time grows automatically, without any change in the total hours worked. How is necessary labour time shortened? Only by reducing the value of labour-power itself. The value of labour-power is determined by the cost of the goods workers need to reproduce themselves — food, clothing, shelter. If the productivity of industries producing those goods rises, those goods become cheaper, the value of labour-power falls, and workers reproduce their wages in less time. The surplus portion of the day expands. No individual capitalist sets out to cheapen labour-power in general. Each simply tries to beat their competitors by cutting unit costs through higher productivity. But the aggregate social effect of each capitalist's competitive drive is exactly this: the general cheapening of wage-goods, the falling value of labour-power, the expansion of relative surplus-value across the whole economy. This is the mechanism behind the long historical trend of rising productivity combined with stagnant or falling real wages. The gains from increased productive power accrue overwhelmingly to capital, because the competitive pressure that drives productivity simultaneously drives down the value of what workers are paid in. Relative surplus-value is the form that surplus extraction takes once absolute extension of the working day meets its limits.