The third volume of Sohn-Rethel's writings contains the earliest elaborations of his critique of knowledge, the problematic of which was to remain the central focus of his intellectual work throughout his life. The fundamental idea that Kant's transcendental subject is a fetish concept of the capital function of money occurred to Sohn-Rethel as early as the early 1920s. Or, to put it differently: 1921: Postulate: the commodity form comprehends the transcendental subject within itself. The form of thought results from the commodity form: abstract thinking, to which Sohn-Rethel's critique of ideology serves as an extension of Marx's critique of the fetish character of the commodity, has its roots in exchange abstraction.