Objection 2: Further, it is written ( James 3:16 ): "Where jealousy [Douay: 'envy'] and contention are, there are inconstancy and every evil work." But jealousy pertains to envy. Therefore inconstancy pertains not to imprudence but to envy.
Objection 3: Further, a man would seem to be inconstant who fails to persevere in what he has proposed to do. Now this is a mark of "incontinency" in pleasurable matters, and of "effeminacy" or "squeamishness" in unpleasant matters, according to Ethic. vii, 1. Therefore inconstancy does not pertain to imprudence.
On the contrary, It belongs to prudence to prefer the greater good to the lesser. Therefore to forsake the greater good belongs to imprudence. Now this is inconstancy. Therefore inconstancy belongs to imprudence.
I answer that, Inconstancy denotes withdrawal from a definite good purpose. Now the origin of this withdrawal is in the appetite, for a man does not withdraw from a previous good purpose, except on account of something being inordinately pleasing to him: nor is this withdrawal completed except through a defect of reason, which is deceived in rejecting what before it had rightly accepted. And since it can resist the impulse of the passions, if it fail to do this, it is due to its own weakness in not standing to the good purpose it has conceived; hence inconstancy, as to its completion, is due to a defect in the reason. Now just as all rectitude of the practical reason belongs in some degree to prudence, so all lack of that rectitude belongs to imprudence. Consequently inconstancy, as to its completion, belongs to imprudence. And just as precipitation is due to a defect in the act of counsel, and thoughtlessness to a defect in the act of judgment, so inconstancy arises from a defect in the act of command. For a man is stated to be inconstant because his reason fails in commanding what has been counselled and judged.
Reply to Objection 1: The good of prudence is shared by all the moral virtues, and accordingly perseverance in good belongs to all moral virtues, chiefly, however, to fortitude, which suffers a greater impulse to the contrary.
Reply to Objection 2: Envy and anger, which are the source of contention, cause inconstancy on the part of the appetite, to which power the origin of inconstancy is due, as stated above.
Reply to Objection 3: Continency and perseverance seem to be not in the appetitive power, but in the reason. For the continent man suffers evil concupiscences, and the persevering man suffers grievous sorrows (which points to a defect in the appetitive power); but reason stands firm, in the continent man, against concupiscence, and in the persevering man, against sorrow. Hence continency and perseverance seem to be species of constancy which pertains to reason; and to this power inconstancy pertains also.
Whether the aforesaid vices arise from lust?
Objection 1: It would seem that the aforesaid vices do not arise from lust. For inconstancy arises from envy, as stated above (A[5], ad 2). But envy is a distinct vice from lust.
Objection 2: Further, it is written ( James 1:8 ): "A double-minded man is inconstant in all his ways." Now duplicity does not seem to pertain to lust, but rather to deceitfulness, which is a daughter of covetousness, according to Gregory (Moral. xxxi, 45). Therefore the aforesaid vices do not arise from lust.
Objection 3: Further, the aforesaid vices are connected with some defect of reason. Now spiritual vices are more akin to the reason than carnal vices. Therefore the aforesaid vices arise from spiritual vices rather than from carnal vices.
On the contrary, Gregory declares (Moral. xxxi, 45) that the aforesaid vices arise from lust.
I answer that, As the Philosopher states (Ethic. vi, 5) "pleasure above all corrupts the estimate of prudence," and chiefly sexual pleasure which absorbs the mind, and draws it to sensible delight. Now the perfection of prudence and of every intellectual virtue consists in abstraction from sensible objects. Wherefore, since the aforesaid vices involve a defect of prudence and of the practical reason, as stated above (AA[2],5), it follows that they arise chiefly from lust.
Reply to Objection 1: Envy and anger cause inconstancy by drawing away the reason to something else; whereas lust causes inconstancy by destroying the judgment of reason entirely. Hence the Philosopher says (Ethic. vii, 6) that "the man who is incontinent through anger listens to reason, yet not perfectly, whereas he who is incontinent through lust does not listen to it at all."
Reply to Objection 2: Duplicity also is something resulting from lust, just as inconstancy is, if by duplicity we understand fluctuation of the mind from one thing to another. Hence Terence says (Eunuch. act 1, sc. 1) that "love leads to war, and likewise to peace and truce."
Reply to Objection 3: Carnal vices destroy the judgment of reason so much the more as they lead us away from reason.