This article clarifies and resituates Althusser’s materialist philosophical project in relation not only to such predecessors as V.I. Lenin and Jean-Toussaint Desanti but also to such successors as Pierre Macherey and Pierre Raymond. The thesis of the article is that Althusser’s project to establish a philosophical practice that would be appropriate for Marxism did not simply consist of identifying and defending a ‘materialist’ position in philosophy against external ‘idealist’ challenges or threats. On the contrary, it recognised that there exists an interminable struggle between inextricably linked but ever-shifting materialist and idealist tendencies – a struggle that operates as a defining feature in the history of philosophy. As a result, the problem explored in this article concerns how best to conceptualise this struggle and to determine whether or not the term ‘tendency’ genuinely holds analytical value and can serve as an important conceptual resource for Marxists working within the field of philosophy.