Marginal Productivity and the Demand for Labour

The theory of the determination of wages in a free market is simply a special case of the general theory of value. Wages are the price of labour; and thus, in the absence of control, they are determined, like all prices, by supply and demand. The need for a special theory of wages only arises because both the supply of labour, and the demand for it, and the way in which demand and supply interact on the labour market, have certain peculiar properties, which make it impossible to apply to labour the ordinary theory of commodity value without some further consideration.