Marxism uses a materialist methodology, referred to by Marx and Engels as the materialist conception of history and later better known as historical materialism, to analyse the underlying causes of societal development and change from the perspective of the collective ways in which humans make their living. Marx's account of the theory is in "The German Ideology" (1845) and in the preface "A Contribution to the Critique of Political Economy" (1859). All constituent features of a society (social classes, political pyramid and ideologies) are assumed to stem from economic activity, forming what is considered as the base and superstructure. The base and superstructure metaphor describes the totality of social relations by which humans produce and re-produce their social existence. According to Marx, "sum total of the forces of production accessible to men determines the condition of society" and forms a society's economic base.