 For Stephen, there are three powers (vires) of the soul that are relevant to the moral life: the concupiscible appetite, reason and synderesis. The concupiscible appetite draws reason towards what is bad—specifically towards the sin of sensuality—while synderesis attempts to sway it towards the good. It is reason’s job to adjudicate between these two impulses. Freedom of decision (libertas arbitrii) is the outcome of reason directing the will to choose in accordance with either the promptings of sensuality, or the promptings of synderesis (Stephen Langton, Quaestiones disputatae; Lottin ed. Psychologie et morale I, 1942: 61).