I like to point out that Marx had sense. Engels lent him the necessary pence.
The Unpaid Working Day As The Source Of Surplus ValueAs demonstrated by Ian Steedman in the 1970s, the working day can be broken out into time paid to the worker and unpaid time. Steedman is echoing results established previously by Michio Morishima.
This decomposition takes the technique in use as given. A complication arises for the general case of joint production. The production of wool and mutton, both from sheep, is often cited as an example of joint production. The proper treatment of fixed capital, such as lathes and other machinery, is another example of joint production.
When calculating the part of the day that is required to produce the commodities that the workers buy out of their wages, the technique is not given. In the circulating capital case, the processes being operated, are scaled down. But in the case of general joint production, a different set of processes might be operated. The labor required to produce a net product of a given commodity basket, contrary to Marx, is not a sum of the labor values of the commodities in the basket. An explanation is provided in the closing chapters of Morishima's and Steedman's respective books. The labor required to produce a commodity basket is the solution of a linear program (LP) in which the processes are operated to produce the basket such that labor input is a minimum.
The decomposition of the working day is not dependent on Marx's theory of value. The unpaid part of the working day is the source of surplus, part of which is paid out as the revenue of the capitalist.
Illusions Of The MarketThis decomposition of the working day is not necessarily apparent. The employer of a worker at Walmart sees they are being paid so much an hour. All of labor appears to be paid. Marx is quite aware of this appearance:
"Hence, we may understand the decisive importance of the transformation of value and price of labour-power into the form of wages, or into the value and price of labour itself. This phenomenal form, which makes the actual relation invisible, and, indeed, shows the direct opposite of that relation, forms the basis of all the juridical notions of both labourer and capitalist, of all the mystifications of the capitalistic mode of production, of all its illusions as to liberty, of all the apologetic shifts of the vulgar economists." -- Karl Marx, Capital, Vol. 1, chap 19.
These necessary illusions are not just for wages. A financial analyst does not calculate the rate of return for a firm based on how much a company expends on payroll. Rather the entire capital investment is examined, with conventional accounting for depreciation.
Here is another apposite paragraph from Marx:
"Vulgar economy actually does no more than interpret, systematise and defend in doctrinaire fashion the conceptions of the agents of bourgeois production who are entrapped in bourgeois production relations. It should not astonish us, then, that vulgar economy feels particularly at home in the estranged outward appearances of economic relations in which these prima facie absurd and perfect contradictions appear and that these relations seem the more self-evident the more their internal relationships are concealed from it, although they are understandable to the popular mind. But all science would be superfluous if the outward appearance and the essence of things directly coincided. Thus, vulgar economy has not the slightest suspicion that the trinity which it takes as its point of departure, namely, land - rent, capital - interest, labour - wages or the price of labour, are prima facie three impossible combinations." -- Karl Marx, Capital, Vol 3, chap 48: The Trinity Formula
It is no refutation of Marx to note that things look different in appearance.
Concluding ObservationsI try to read Marx under the influence of the later Wittgenstein. Some sort of deeper essence does not exist that appears in empirical reality. Marx tries to be more systematic than Wittgenstein, but both are gathering observations for a purpose. Only a change in our form of life will remove the need for these reminders.