An excerpt of a passage from the Grundrisse, in the notorious "fragment on machines," has become iconic in contemporary Marx studies:
Capital itself is the moving contradiction, [in] that it presses to reduce labour time to a minimum, while it posits labour time, on the other side, as sole measure and source of wealth. Hence it diminishes labour time in the necessary form so as to increase it in the superfluous form; hence posits the superfluous in growing measure as a condition – question of life or death – for the necessary. On the one side, then, it calls to life all the powers of science and of nature, as of social combination and of social intercourse, in order to make the creation of wealth independent (relatively) of the labour time employed on it. On the other side, it wants to use labour time as the measuring rod for the giant social forces thereby created, and to confine them within the limits required to maintain the already created value as value. Forces of production and social relations – two different sides of the development of the social individual – appear to capital as mere means, and are merely means for it to produce on its limited foundation. In fact, however, they are the material conditions to blow this foundation sky-high.
I have highlighted in green part of the passage that Moishe Postone quoted twice in his Time, Labor and Social Domination. For Postone, the passage had profound emancipatory implications. The second citation precedes the climax of his interpretation of Marx's theory. The category of "superfluous labor time" is central to Postone's interpretation:
The difference between the total labor time determined as socially necessary by capital, on the one hand, and the amount of labor that would be necessary, given the development of socially general productive capacities, were material wealth the social form of wealth, on the other, is what Marx calls in the Grundrisse "superfluous" labor time.
Postone's speculation about the amount of labour time that "would be necessary" unwittingly reverts to Dilke's (and Godwin's) concept of consumption-based social necessity that Marx implicitly critiqued with his category of socially necessary labour time. Although it isn't self-evident from the Grundrisse passage, Marx's use of superfluous here is more likely to refer primarily to superfluous labour capacity rather than merely superfluous production. Granted the latter is implied by the former but Marx's analysis points to relative surplus population, the disposable industrial reserve army, as capital's instintive reflex.
Marx cited The Source and Remedy of the National Difficulties immediately after the paragraph about capital's "moving contradiction" but Postone didn't mention the pamphlet anywhere in his book. Marx's juxtaposition of the superfluous as a condition for the necessary with Dilke's exaltation of disposable time is too central to Marx's point to be glossed over. What superfluous (überflüssig) refers to here can best be understood from the recognition that there are not one but three pertinent fragments on machines in the Grundrisse that examine the contradictions of überflüssig and notwendig labour power and labour time.
Those fragments can be found on pages 397-401, 608-610, and 690-712 (especially pp. 704-709) of the 1973 English translation of Grundrisse by Martin Nicolaus, published by Penguin Books. Marx did mention surplus population in the pp. 690-712 fragment:
As the magnitude of relative surplus labour depends on the productivity of necessary labour, so does the magnitude of labour time – living as well as objectified – employed on the production of fixed capital depend on the productivity of the labour time spent in the direct production of products. Surplus population (from this standpoint), as well as surplus production, is a condition for this. That is; the output of the time employed in direct production must be larger, relatively, than is directly required for the reproduction of the capital employed in these branches of industry. The smaller the direct fruits borne by fixed capital, the less it intervenes in the direct production process, the greater must be this relative surplus population and surplus production; thus, more to build railways, canals, aqueducts, telegraphs etc. than to build the machinery directly active in the direct production process. Hence – a subject to which we will return later – in the constant under- and overproduction of modern industry – constant fluctuations and convulsions arise from the disproportion, when sometimes too little, then again too much circulating capital is transformed into fixed capital.
The pp. 608-610 fragment is more explicit about the relationship between necessary labour (individual and social), superfluous labour power, and surplus population:
The expression, surplus population, concerns exclusively labour capacities, i.e. the necessary population; surplus of labour capacities. But this arises simply from the nature of capital. Labour capacity can perform its necessary labour only if its surplus labour has value for capital, if it can be realized by capital. Thus, if this realizability is blocked by one or another barrier, then (1) labour capacity itself appears outside the conditions of the reproduction of its existence; it exists without the conditions of its existence, and is therefore a mere encumbrance; needs without the means to satisfy them; (2) necessary labour appears as superfluous, because the superfluous is not necessary. It is necessary only to the extent that it is the condition for the realization of capital.
Thus the relation of necessary and surplus labour, as it is posited by capital, turns into its opposite, so that a part of necessary labour – i.e. of the labour reproducing labour capacity – is superfluous, and this labour capacity itself is therefore used as a surplus of the necessary working population, i.e. of the portion of the working population whose necessary labour is not superfluous but necessary for capital.
Since the necessary development of the productive forces as posited by capital consists in increasing the relation of surplus labour to necessary labour, or in decreasing the portion of necessary labour required for a given amount of surplus labour, then, if a definite amount of labour capacity is given, the relation of necessary labour needed by capital must necessarily continuously decline, i.e. part of these labour capacities must become superfluous, since a portion of them suffices to perform the quantity of surplus labour for which the whole amount was required previously. The positing of a specific portion of labour capacities as superfluous, i.e. of the labour required for their reproduction as superfluous, is therefore a necessary consequence of the growth of surplus labour relative to necessary.
The pp. 397-401 fragment offers more elaboration on the historical evolution of superfluous labour time and its expression, under capital, as surplus population:
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.
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.
In closing, I want to acknowledge that Moishe Postone's critique of "traditional Marxism" and his analysis of this particular passage were crucial to my deeper understanding of Capital and the Grundrisse. My critique of Postone's interpretation of this passage doesn't unravel the importance of his contribution.
In the same vein, it is my view that Marx's critique of political economy owed far more than has been previously acknowledged to the 1821 pamphlet, The Source and Remedy of the National Difficulties and especially to those two things "our pamphleteer" overlooked that, in my opinion, laid the cornerstone for Marx's critique. It was Postone's omission of Marx's quotation of the pamphlet that sent me to the library to ferret out the microfilm copy a couple of decades ago.