Although it was, until recently, unfashionable in certain circles to say this, Marx was not a philosopher in any interesting sense. He was a social theorist. As social theory, I am thinking primarily of two areas (in all social theory, there is also a large body of empirical work, which I am not competent to comment upon): (a) the methodology of social inquiry, and its metaphysical presuppositions, and (b) normative philosophy (ethics and political theory).

Many social theorists are also philosophers: Hobbes, Locke, Hegel and Mill provide good examples. They articulate and develop a general philosophy, a metaphysics and an epistemology, and typically their social theory relies in essential ways on that general philosophy, or at any rate they believe that it does. There is a connection, for example, between Mill's empiricism, on the one hand, and, on the other, both his utilitarian philosophy, and the methodology of social science that he outlines in Book VI of his A System of Logic.

Marx also believed that his social theory depended on certain philosophical assumptions, but, unlike these aforementioned social theorists, he does not, for the most part, articulate or develop in any significant way the philosophy on which he believes his social theory depends.