Correspondence exchanged between Louis Althusser and Lucien Sève from 1949 to 1987 must be considered from three different but inseparable stand-points : a friendship never being denied until the end of exchanges, a political companionship as both were Pcf members, and rather early-appearing theoretical divergences. Four periods may be distinguished, the second period, 1962-1973, is decisive and concludes with the impossibility of agreement between conceiving a Marxist doctrine as inseparable from a theoretical anthropology based essentially but not entirely on Man at work (Sève) and theorizing the historical materialism as no meeting Man (or Men) during its conceptual elaboration, because the psychic reality to whom psychoanalysis introduces proceeds from another area, very far from the area of the sciences of social formations in a strong sense (Althusser).