Instrumental reason concentrates on effective means to given ends while relegating the question of which ends deserve pursuit. In Eclipse of Reason, Horkheimer criticizes the reduction of reason to calculation and adaptation.
Speeding up production may be technically successful while leaving unanswered which needs are met, whose time is consumed, or what environmental effects follow. The target is not calculation itself but its substitution for the evaluation of purposes.
Equating instrumental rationality directly with technology or science oversimplifies the argument. Horkheimer examines the social organization of reason and domination, including the management of external nature and people’s treatment of their own needs as objects of adaptation.
Habermas later reconstructs the problem by distinguishing purposive action from action oriented towards mutual understanding. This does not endorse all of Horkheimer’s claims. The term’s historical and theoretical scope must remain explicit when moving between their approaches.