In his Grundrisse, Marx identified surplus labour time as a form of disposable time. That is to say that, under capitalism, it is labour time at the disposal of capital. "The whole development of wealth," Marx wrote, "rests on the creation of disposable time." "In production resting on capital," he continued three sentences later, "the existence of necessary labour time is conditional on the creation of superfluous labour time."
Although it strongly suggests surplus labour time -- and thus surplus value -- superfluous labour time is not identical to surplus labour time. In the Grundrisse, Marx discussed disposable time and superfluous labour time as characteristics of any human society, not exclusively historical capitalism. It is the unique characteristic of capitalism that it subordinates the performance of necessary labour to the production of surplus value. Thus, under capitalism, superfluous labour time takes on a new function, a large part of which is indeed the production of surplus value. But that is not all, as Marx explained two paragraphs later. In its drive to create as much surplus labour as possible and "to reduce necessary labour to a minimum," capital also has a tendency "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." Superfluous labour time thus implies surplus population alongside surplus labour time.
Regardless of whether one works for a wage or is unemployed, the capacity to perform labour is the outcome of an intrinsically social, co-operative activity. As such, this capacity can best be understood, at least in part, as a "common-pool resource" in that it may most effectively be engaged, valued, enjoyed and protected as a collectively-shared asset rather than as a fragmented assortment of individualized units, which is the current model of labour-as-a-commodity. Relating the concept of a common-pool good to labour is especially apt in that it illuminates, as Burkett points out, "the parallel between capital's extension of work time beyond the limits of human recuperative abilities [including social vitality], and capital's overstretching of the regenerative powers of the land." However, there is also an important distinction between wealth, which can be accumulated and preserved, and those subsistence goods that must be consumed directly to sustain life and enable work to continue. Social production would cease if the producers themselves were denied the goods necessary to their sustenance. Therefore it would be logical to regard only the produce of disposable time, that is superfluous labour time, as goods held in common.