It is worth noting, then, that nowhere in his unpublished notebooks did Marx actually assemble this array of anatomically distinct forms of society into a progressive historical sequence- instead, they lay side by side, synchronically. Their arrangement into a diachronic sequence can be found in another work published shortly after, A Contribution to a Critique of Political Economy, whose preface provides the clearest statement of what Marx meant by historical materialism in the period prior to the conceptual breakthroughs which organize the later study, Capital.
"Mankind thus inevitably sets itself only such tasks as it is able to solve, since closer examination will always show that the problem itself arises only when the material conditions for its solution are already present or at least in the course of formation. In broad outline, the Asiatic, ancient, feudal, and modern bourgeois modes of production may be designated as epochs marking progress in the economic development of society. The bourgeois mode of production is the last antagonistic form of the social process of production – antagonistic not in the sense of individual antagonism but of an antagonism that emanates from the individuals' social conditions of existence – but the productive forces developing within bourgeois society also create the material conditions for a solution of this antagonism. The prehistory of human society accordingly closes with this social formation."1
