In the following article I am going to defend the thesis, which at first may appear to be strange, that, in order to base sociology (and knowledge) on Marxian epistemology one has to accept on an ontological level the position of methodological individualism, and on a metatheoretical level a position of non-reductionism 1. In order to support my thesis I have to explicate briefly: 1) Marx's basic epistomological position. 2) the principle of methodological individualism, where I try to differentiate between a reified and a nonreified version2, and 3) the position of non-reductionism.