If surplus labour-time is that part of the working day in excess of necessary labour-time, it assumes a form of existence as “a multiplication of simultaneous working days, i.e. of the labouring population.” To the extent, therefore, that the relation between necessary and surplus labour-time can be modified through transformations in the social productivity of labour, this latter can also change the composition of the population. “A labouring population of, say, 6 million can be regarded as one working day of 6 × 12, i.e. 72 million hours: so that the same laws [are] applicable here.”

If it is a law of capital that it sets surplus labour in motion, it can only do this on the basis of setting necessary labour in motion. This in turn is achieved through the exchange of capital with labour. The tendency of capital is to create as much labour as possible, at the same time as to reduce necessary labour to a minimum. It is therefore also a tendency of capital to create a surplus population.

More (pdf, 79 KB): The Chapter on Capital: Part 17: The Accumulation of Capital and the Law of Population (pp. 398-401)