'Property. Origin in the productivity of labour. If one can produce only enough for one, everyone worker; there can be no property. When one man's labour can maintain five, there will be four idle men for one employed in production. Property grows from the improvement in the mode of production ... The growth of the property, this greater ability to maintain idle men and unproductive industry = capital ... machinery itself can seldom be applied with success to abridge the labours of an individual: more time would be lost in its construction than could be saved by its application. It is only really useful when it acts on great masses. when a single machine can assist the labours of thousands. It is accordingly in the most populous countries where there are most idle men that it is always most abundant. It is not called into action by scarcity of men, but by the facility with which they are brought together ... Not 1/4 of the English population provides everything that is consumed by all. Under William the Conqueror for example the amount of those directly participating in production much greater relative to the idle men.' (Ravenstone, IX, 32.) Just as capital on one side creates surplus labour, surplus labour is at the same time equally the presupposition of the existence of capital. The whole development of wealth rests on the creation of disposable time. The relation of necessary labour time to the superfluous (such it is, initially, from the standpoint of necessary labour) changes with the different stages in the development of the productive forces. In the less productive  stages of exchange, people exchange nothing more than their superfluous labour time; this is the measure of their exchange, which therefore extends only to superfluous products. In production resting on capital, the existence of necessary labour time is conditional on the creation of superfluous labour time. In the lowest stages of production, firstly, few human needs have yet been produced, and thus few to be satisfied. Necessary labour is therefore restricted, not because labour is productive, but because it is not very necessary; and secondly, in all stages of production there is a certain common quality [Gemeinsamkeit] of labour, social character of the same, etc. The force of social production develops later etc. (Return to this.) 
Increase of surplus labour time. Increase of simultaneous working days (Population). (Population can increase in proportion as necessary labour time becomes smaller, i.e. the time required to produce living labour capacities decreases.) Surplus capital and surplus population. -- Creation of free time for society
Surplus time is the excess of the working day above that part of it which we call necessary labour time; it exists secondly as the multiplication of simultaneous working days, i.e. of the labouring population. (It can also be created - but this is mentioned here only in passing, belongs in the chapter on wage labour - by means of forcible prolongation of the working day beyond its natural limits; by the addition of women and children to the labouring population.) The first relation, that of the surplus time and the necessary time in the day, can be and is modified by the development of the productive forces, so that necessary labour is restricted to a constantly smaller fractional part. The same thing then holds relatively for 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 applicable here.
It is a law of capital, as we saw, to create surplus labour, disposable time; it can do this only by setting necessary labour in motion—i.e. entering into exchange with the worker. It is its tendency, therefore, to create as much labour as possible; just as it is equally its tendency to reduce necessary labour to a minimum. It is therefore equally a tendency of capital to increase the labouring population, as well as constantly to posit a part of it as surplus population—population which is useless until such time as capital can utilize it. (Hence the correctness of the theory of surplus population and surplus capital.) It is equally a tendency of capital to make human labour (relatively) superfluous, so as to drive it, as human labour, towards infinity. Value is nothing but objectified labour, and surplus value (realization of capital) is only the excess above that part of objectified labour which is necessary for the reproduction of labouring capacity. But labour as such is and remains the presupposition, and surplus labour exists only in relation with the necessary, hence only in so far as the latter exists. Capital must therefore constantly posit necessary labour in order to posit surplus labour; it has to multiply it (namely the simultaneous working days) in order to multiply the surplus; but at the same time it must suspend them as necessary, in order to posit them as surplus labour. As regards the single working day, the process is of course simple: (1) to lengthen it up to the limits of natural possibility; (2) to shorten the necessary part of it more and more (i.e. to increase the productive forces without limit). But the working day, regarded spatially—time itself regarded as space—is many working days alongside one another. The more working days capital can enter into exchange with at once, during which it exchanges objectified for living labour, the greater its realization at once. It can leap over the natural limit formed by one individual's living, working day, at a given stage in the development of the forces of production (and it does not in itself change anything that this stage is changing) only by positing another working day alongside the first at the same time - by the spatial addition of more simultaneous working days. E.g. I can drive the surplus labour of A no higher than 3 hours; but if I add the days of B, C, D etc., then it becomes 12 hours. In place of a surplus time of 3, I have created one of 12. This is why capital solicits the increase of population; and the very process by means of which necessary labour is reduced makes it possible to put new necessary labour (and hence surplus labour) to work. (I.e. the production of workers becomes cheaper, more workers can be produced in the same time, in proportion as necessary labour time becomes smaller or the time required for the production of living labour capacity becomes relatively smaller. These are identical statements.) (This still without regard to the fact that the increase in population increases the productive force of labour, since it makes possible a greater division and combination of labour etc. The increase of population is a natural force of labour, for which nothing is paid. From this standpoint, we use the term natural force to refer to the social force. All natural forces of social labour are themselves historical products.) It is, on the other side, a tendency of capital—just as in the case of the single working day—to reduce the many simultaneous necessary working days (which, as regards their value, can be taken as one working day) to the minimum, i.e. to posit as many as possible of them as not necessary. Just as in the previous case of the single working day it was a tendency of capital to reduce the necessary working hours, so now the necessary working days are reduced in relation to the total amount of objectified labour time. (If 6 are necessary to produce 12 superfluous working hours, then capital works towards the reduction of these 6 to 4. Or 6 working days can be regarded as one working day of 72 hours; if necessary labour time is reduced by 24 hours, then two days of necessary labour fall away—i.e. 2 workers.) At the same time, the newly created surplus capital can be realized as such only by being again exchanged for living labour. Hence the tendency of capital simultaneously to increase the labouring population as well as to reduce constantly its necessary part (constantly to posit a part of it as reserve). And the increase of population itself the chief means for reducing the necessary part. At bottom this is only an application of the relation of the single working day. Here already lie, then, all the contradictions which modern population theory expresses as such, but does not grasp. Capital, as the positing of surplus labour, is equally and in the same moment the positing and the not-positing of necessary labour; it exists only in so far as necessary labour both exists and does not exist. [*]
If the relation of the necessary working days to the total number of objectified working days was = 9:12 (hence surplus labour = 1/4), then the striving of capital is to reduce it to 6:9 (i.e. 2/3, hence surplus labour = 1/3). (Develop this more closely later; still, the major basic traits here, where we are dealing with the general concept of capital.)