This article provides a reconstruction of the theory of abstraction elaborated by Louis Althusser in two recently published book manuscripts of the second half of the 1970s, Être marxiste en philosophie (1976, published in 2015) and Initiation à la philosophie pour les non-philosophes (1978, published in 2014). It focuses in particular on the practical character of abstraction, or more precisely, on the plurality of abstractive practices explored by Althusser, contrasting it with Marxian theories of real abstraction, as well as with Althusser's own theory of “Generalities” in For Marx, and touching on whether with his account of abstraction in language Althusser was drifting into a philosophical anthropology. It argues that these manuscripts, starting from the thesis that philosophy began in ancient Greece with a reaction against the subversive character of mathematics, delineate another materialist practice of philosophy, founded on detotalization and oriented towards the question of communist transition.