In the course of explaining to Boso why God must have created man in a state of righteousness, Anselm (Cur deus homo) analyzes rational nature. Rationality is a power of discrimination (potestatem discernendi), and particularly a power of moral discrimination: It distinguishes right and wrong (iustum et iniustum), good and evil (bonum et malum) and also between the greater and lesser good (maius . . . minus). Reason is the capacity to distinguish the evils that should be hated from the goods that should be loved, and to distinguish between the lesser goods that should be loved less and the greatest good that should be loved and chosen for its own sake (summum bonum super omnia amaret et eligeret). Rationality guides attachments (to goods that are to be loved) and avoidances (of evils that are to be hated).
Rationality is not linked primarily to deduction, induction, or any other logical procedure. It is a power of judgment, evaluation, and assessment, and it is in service of the choices and loves of the will. Once again there are aesthetic resonances to Anselm’s argument, as reason verges close to aesthetic sense and is construed as something like “moral taste.”