The only extensive discussion of Marx's concepts (or categories) and the conception of social reality which finds expression in them appears in his unfinished Introduction to the Critique of Political Economy. This seminal work, which was first published by Karl Kautsky in 1903, has been unjustly ignored by most Anglo-Saxon writers on Marxism. Here we learn that ‘In the study of economic categories, as in the case of every historical and social science, it must be borne in mind that as in reality so in our mind the subject, in this case modern bourgeois society, is given and that the categories are therefore but forms of expression, manifestations of existence, and frequently but one-sided aspects of this subject, this definite society.’ This distinction between subject and categories is simple recognition of the fact that our knowledge of the real world is mediated through the construction of concepts in which to think about it; our contact with reality, in so far as we become aware of it, is contact with a conceptualized reality.

What is unusual in Marx's statement is the special relation he posits between categories and society. Instead of being simply a means for describing capitalism (neutral vehicles to carry a partial story), these categories are declared to be ‘forms’, ‘manifestations’ and ‘aspects’ of their own subject matter. Or, as he says elsewhere in this Introduction, the categories of bourgeois society ‘serve as the expression of its conditions and the comprehension of its own organization’.