Formal subsumption remains merely formal precisely in the sense that it does not involve capital’s transformation of a given labour process, but simply its taking hold of it. Capital can extract surplus value from the labour process simply as it is given — with its given productivity of labour — but it can do so only insofar as it can extend the social working day beyond what must be expended on necessary labour. It is for this reason that formal subsumption alone could only ever yield absolute surplus value: the absoluteness of absolute surplus value lies in the fact that its extraction involves an absolute extension of the social working day — it is a simple quantity in excess of what is socially necessary for workers to reproduce themselves.12
The subsumption of the labour process under the valorisation process of capital becomes “real” insofar as capital does not merely rest with the labour process as it is given, but steps beyond formal possession of that process to transform it in its own image. Through technological innovations and other alterations in the labour process, capital is able to increase the productivity of labour. Since higher productivity means that less labour is required to produce the goods which the working class consumes, capital thereby reduces the portion of the social working day devoted to necessary labour, and concomitantly increases that devoted to surplus labour. The relativity of relative surplus value lies in the fact that the surplus part of the social working day may thus be surplus relative to a decreasing necessary part, meaning that capital may valorise itself on the basis of a given length of social working day — or even one that is diminished in absolute length.13 The production of relative surplus-value, and the real subsumption through which this takes place, are driven by the competition between capitals: individual capitalists are spurred on to seize the initiative by the fact that, while the value of commodities is determined by the socially necessary labour-time for their production, if they introduce technological innovations which increase the productivity of labour, they will be able to sell commodities at a price above their “individual value”.
Despite their usage by Marx in close association with systematic categories like absolute and relative surplus-value, and their abstract philosophical provenance, there are at least two senses here in which we may consider the categories of formal and real subsumption to have a “historical” significance. Firstly, as capital’s simple taking hold of the labour process, the formal subsumption of labour under capital can be understood as the transition to the capitalist mode of production: it is “the subsumption under capital of a mode of labour already developed before the emergence of the capital-relation”.15 Marx describes the transformation of slave, peasant, guild and handicraft forms of production into capitalist production — as producers associated with these forms were transformed into wage-labourers — as a process of formal subsumption. It is only on the basis of this formal subsumption that real subsumption can proceed historically: formal subsumption of labour under capital is both a logical/systematic and a historical prerequisite for real subsumption.
Secondly, real subsumption has a historical directionality, for it entails a constant process of revolutionising the labour process through material and technological transformations which increase the productivity of labour. From these secular increases in productivity follow broader transformations in the character of society as a whole, and in the relations of production between workers and capitalists in particular. Real subsumption, as the modification of the labour-process along specifically capitalist lines, is exemplified in the historical development of the productive powers of social labour as the productive powers of capital. This occurs through cooperation, the division of labour and manufacture, machinery and large-scale industry, all of which are discussed by Marx under the heading of “The Production of Relative Surplus-Value” in volume one of Capital.
The work of some theorists in the area of value-form theory or systematic dialectic — such as Patrick Murray and Chris Arthur — puts such periodisation further in doubt. For Arthur, though formal subsumption may well precede real subsumption temporally in the case of any given capital, real subsumption is inherent to the concept of capital from the outset.35 If real subsumption is thus something always implicit, which is only actualised in the course of capitalist history, this would further undermine any attempt to demarcate a specific period of real subsumption. Murray argues that the terms “formal subsumption” and “real subsumption” refer first to concepts of subsumption and only secondarily — if at all — to historical stages. According to Murray, Marx considers the possibility of a distinct historical stage of merely formal subsumption, but finds no evidence of one.36