INCONSTANCY. — From the Latin *inconstantia* (not constancy), meaning fickleness, is a vice opposed to prudence, inasmuch as it leads one to change judgment without reason. The initial motive for such change lies in appetite, which impels one to abandon the first good resolve in view of something that seems more pressing; but the true cause of it is the defect of reason, which repudiates what it had previously accepted, through weakness in resisting the impulse of passion, to which it could and should resist.
It follows that inconstancy is a defect of reason that fails in commanding what has already been counselled and judged. Inconstancy, therefore, is a vice contrary to prudence by defect, and more properly to that activity of prudence (imperium) by which the intellect proposes its judgment to the will as that which must be executed (*Summa Theologiae*, 2a-2ae, q. 47, a. 8; q. 53, a. 5).
Inconstancy is also an internal vice that proceeds from lust, inasmuch as man, driven by concupiscence and the love of lascivious things, is hindered from carrying out what he had decided to do; for example, to avoid the proximate occasion of sin. It is the vice of that man who vainly promises to distance himself from a dangerous person, to whom Terence (*Eunuchus*, 67-9) repeats in tones of reproach: *"Haec verba una... falsa lacrimula... re-tinguet"* (cf. *Summa Theologiae*, 2a-2ae, q. 153, a. 5).