Let us take an aliquot part of capital upon which we calculate the rate of
 profit, e.g., 100. These 100 represent the average composition of the
 total capital, say, 80c + 20v. We
 have seen in the second part of this book that the average rate of profit in
 the various branches of production is determined not by the particular
 composition of each individual capital, but by the average social composition.
 As the variable capital decreases relative to the constant, hence the total
 capital of 100, the rate of profit, or the relative magnitude of surplus-value,
 i.e., its ratio to the advanced total capital of 100, falls even
 though the intensity of exploitation were to remain the same, or even to
 increase. But it is not this relative magnitude alone which falls. The
 magnitude of the surplus-value or profit absorbed by the total capital of 100
 also falls absolutely. At a rate of surplus-value of 100%, a capital of 60c + 40v produces a mass of
 surplus-value, and hence of profit, amounting to 40; a capital of 80c + 20v a mass of profit of 30; and for
 a capital of 80c + 20v the profit
 falls to 20. This falling applies to the mass of surplus-value, and hence of
 profit, and is due to the fact that the total capital of 100 employs less
 living labour, and, the intensity of labour exploitation remaining the same,
 sets in motion less surplus-labour, and therefore produces less surplus-value.
 Taking any aliquot part of the social capital, i.e., a capital of
 average composition, as a standard by which to measure surplus-value —
 and this is done in all profit calculations — a relative fall of
 surplus-value is generally identical with its absolute fall. In the cases given
 above, the rate of profit sinks from 40% to 30% and to 20%, because, in fact,
 the mass of surplus-value, and hence of profit, produced by the same capital
 falls absolutely from 40 to 30 and to 20. Since the magnitude of the value of
 the capital, by which the surplus-value is measured, is given as 100, a fall in
 the proportion of surplus-value to this given magnitude can be only another
 expression for the decrease of the absolute magnitude of surplus-value and
 profit. This is, indeed, a tautology. But, as shown, the fact that this
 decrease occurs at all, arises from the nature of the development of the
 capitalist process of production.