Near the end of the 1861-63 notebooks Marx returns to the distinction between productive and unproductive labour. The following is a particularly definition of productive labour:
“In the real production process labour is converted in reality into capital, but thisconversion is conditioned by the original exchange between money and labour capacity. It is only through this direct conversion of labour into objectified labour which belongs not to the worker but to the capitalist that the money is converted into capital, including the part which has taken on the form of the means of production, the conditions of labour. Previously money was only capital in itself,†a whether it existed in its own form or in the form of commodities (products) which possessed a shape enabling them to serve as the means of production for new commodities.
It is only this particular relation to labour which converts money or commodity into capital, and that labour is productive labour which — by means of this relation it has to the conditions of production, to which there corresponds a particular position in the real production process — converts money or commodity into capital, i.e. preserves and increases the value of the objective labour which has attained an independent position vis-á-vis labour capacity. Productive labour is only an abbreviation for the whole relation in which, and the manner in which, labour capacity figures in the capitalist production process. It is however of the highest importance to distinguish between this and other kinds of labour, since this distinction brings out precisely the determinate form of labour on which there depends the whole capitalist mode of production, and capital itself. Productive labour, therefore, is labour which — in the system of capitalist production — produces surplus value for its EMPLOYER or which converts the objective conditions of labour into capital, and their owners into capitalists, hence labour which produces its own product as capital. Hence in speaking of productive labour we are speaking of socially determined labour, labour which implies a highly definite relation between the buyer and the seller of labour.
Although the money in the possession of the buyer of labour capacity — or, as a commodity, the buyer of means of production and subsistence for the worker — only becomes capital through the process, is only converted into capital in the process, and therefore these things are not capital before their entry into the process, but are only about to become capital, they are even so capital in themselves; they are capital through the independent shape in which they confront labour capacity and in which labour capacity confronts them, a relation which conditions and ensures the exchange with labour capacity and subsequent process of the real conversion of labour into capital. They already possess at the outset the social determinacy vis-á-vis the workers which makes them into capital and gives them command over labour. They are therefore posited in advance as capital vis-á-vis labour.
Productive labour can therefore be characterised as labour which exchanges directly with money as capital, or, and this is merely an abbreviated expression of the same thing, labour which exchanges directly with capital, i.e. with money which is in itself capital, has the determination of functioning as capital, or confronts labour capacity as capital. The expression “labour which exchanges directly with capital” means that labour exchanges with money as capital and converts it actu†a into capital. What the determination of immediacy implies will soon become more clearly apparent. Productive labour is therefore labour which reproduces for the worker only the previously determined value of his labour capacity, but at the same time, as value- creating activity, it valorises capital or places the values created by labour in confrontation with the worker himself as capital. MECW 34 pp. 130-132