This essay is on the concept of friendship in Aristotle, which plays a key role in his practical philosophy: as a nucleus of human relationships which is the basis not only of politics but of all forms of community, and as that rare element in Aristotelian thought which, at least in part, interrupts the principle of government generally characterizing his system. The author’s argument takes three steps. Beginning with the distinction of individual and collective practice he tries to define the concept of friendship in its tension between the basically different conditions of self-reference and reciprocity. On the basis of this structure, the two communities of oike and polis are reconstructed and a new evaluation of their relationship is attempted. Furthermore, the essay suggests an interpretation of the anthropological dictum: “Man is by nature a political being”, which can integrate both forms of living. Above all, it is pointed out that it was Aristotle who introduced and developed the relationship of ego and alter ego as the nucleus of friendship in practical philosophy. This way he definitely anticipated modern social philosophy with its principal category of intersubjectivity. However, he became entangled in a profound and by no means accidental ambivalence which can be clearly explained.