The capitalist pays the value of the labor power (or, if the price diverges from this, he pays the price) and receives in exchange the right to dispose of the living labor power itself. The length of time during which he utilizes this labor power is divided into two separate parts. During one period, the worker produces a value that is only equal to the value of his labor power, a product of the same price. It is the same as if he had bought the product ready-made in the market. During the other period, the period of surplus labor, the utilization of labor power creates a value for the capitalist without costing him any value in return. He is thus able to set labor power in motion without paying for it. It is in this sense that surplus labor can be called unpaid labor. Capital, therefore, is not only the command over labor, as Adam Smith thought. It is essentially the command over unpaid labor. All surplus value, whatever particular form (profit, interest, rent) it may subsequently crystallize into, is in substance the materialization of unpaid labor time. The secret of the self-valorization of capital resolves itself into the fact that it has at its disposal a definite quantity of the unpaid labor of other people.
Karl Marx, “The Production of Absolute and Relative Surplus-Value”, in Capital, Vol. I, trans. by Ben Fowkes, New York: Penguin, 1990, pp. 671-672.


















