Forced to defend itself against the challenge of ideological pluralism, Marxist philosophy of history soon realized that its assertions concerning the fundamental correlation between the forces and the relations of production (presumably the basis of all historical social forms and the ground of all social being), and its statements concerning the reflection of these forces in the social thought of a political superstructure are ambivalent, and as such imponderable.1 The determinist orientation of the causal primacy of the means of production and the forms of technology in Marx's Critique of Political Economy, the forerunner of his Capital, began to compete with and to be contradicted by the liberal declaration of the Communist Manifesto that all previous history is the record of class struggle. Shortly before the end of the 19th century, Engels noted in his introduction to the new edition of Marx's Class War in France from 1848 to 1850 that the conditions of social conflict had changed since 1850, not only "in reference to civil war but also in regard to class struggle".