This paper develops an alternative to traditional interpretations of M
arx rooted in his 1859 Preface, widely regarded as the definitive summ
ary of his materialist conception of society. It does this by reading
Marx in the light of the ontology of realism and the retroductive mode
of inference. Via an examination of some pivotal texts, centred aroun
d the Grundrisse notebooks, the paper indicates how a realist understa
nding of Marx's retroductive method can be used to reconstruct and dev
elop its creation: Marx's model of capital.