Productive force and the degree of intensity of labour: Marx's concepts and formalizations in the middle part of Capital I

Marx’s account in Capital of the production of surplus-value is examined (Volume I, Parts Three to Five), especially his formalizations in relation to the conceptual progress in the book. It is indicated that his formulas convey theoretical results rather than explanatory processes/mechanisms. This becomes an obstacle particularly when Marx introduces the key concepts of `productive force’ (in modern jargon: technique of production) and `intensity of labour’, leaving behind any simple explanation of value in terms of labour-time. In face of this, the paper sets out an elementary and immanent reconstruction of Marx’s formalization, in which the rate of surplus-value is cast in terms of all of Marx’s main explanatory variables: extensity of labour, wages, productive force and intensity of labour.