The question of the book is how a radical critique of capitalism is possible when critique in the tradition of Kant and Hegel means that the criticized subject itself has to “give” the measure of its critique. The thesis is that, while in Kant this reflexivity is achieved by transcendental subjectivity and reason and in Hegel by self-consciousness, self-relation of the concept and the absolute reason of spirit, in Marx we find a materialist turn.
The turn shows that capitalist society became reflexive by a kind of self-measurement, done by the functions of money, on the one hand, and the valorization of labour power and capital, on the other. Money, by its function as the measure of value and the means of its realization and mediation, measures in the commodities the productive relations of their production, thus determining from the past valorization of labour and capital the magnitudes necessary for their further productive valorization — and hence for a productive use of money itself. That is howl, in money’s capital form, the measured magnitudes become reflexive, while money itself becomes in its capitalist self-relation the form to measures the same valorization process which by this form becomes possible in the first place.