Objection 1. It would seem that the incontinent man sins more gravely than the intemperate. For, seemingly, the more a man acts against his conscience, the more gravely he sins, according to Luke 12:47, "That servant who knew the will of his lord... and did not... shall be beaten with many stripes." Now the incontinent man would seem to act against his conscience more than the intemperate because, according to Ethic. vii, 3, the incontinent man, though knowing how wicked are the things he desires, nevertheless acts through passion, whereas the intemperate man judges what he desires to be good. Therefore the incontinent man sins more gravely than the intemperate.
Objection 2. Further, apparently, the graver a sin is, the more incurable it is: wherefore the sins against the Holy Ghost, being most grave, are declared to be unpardonable. Now the sin of incontinence would appear to be more incurable than the sin of intemperance. For a person's sin is cured by admonishment and correction, which seemingly are no good to the incontinent man, since he knows he is doing wrong, and does wrong notwithstanding: whereas it seems to the intemperate man that he is doing well, so that it were good for him to be admonished. Therefore it would appear that the incontinent man sins more gravely than the intemperate.
Objection 3. Further, the more eagerly man sins, the more grievous his sin. Now the incontinent sins more eagerly than the intemperate, since the incontinent man has vehement passions and desires, which the intemperate man does not always have. Therefore the incontinent man sins more gravely than the intemperate.
On the contrary, Impenitence aggravates every sin: wherefore Augustine says (De Verb. Dom. serm. xi, 12,13) that "impenitence is a sin against the Holy Ghost." Now according to the Philosopher (Ethic. vii, 8) "the intemperate man is not inclined to be penitent, for he holds on to his choice: but every incontinent man is inclined to repentance." Therefore the intemperate man sins more gravely than the incontinent.
I answer that, According to Augustine [De Duab. Anim. x, xi] sin is chiefly an act of the will, because "by the will we sin and live aright" [Retract. i, 9]. Consequently where there is a greater inclination of the will to sin, there is a graver sin. Now in the intemperate man, the will is inclined to sin in virtue of its own choice, which proceeds from a habit acquired through custom: whereas in the incontinent man, the will is inclined to sin through a passion. And since passion soon passes, whereas a habit is "a disposition difficult to remove," the result is that the incontinent man repents at once, as soon as the passion has passed; but not so the intemperate man; in fact he rejoices in having sinned, because the sinful act has become connatural to him by reason of his habit. Wherefore in reference to such persons it is written (Proverbs 2:14) that "they are glad when they have done evil, and rejoice in most wicked things." Hence it follows that "the intemperate man is much worse than the incontinent," as also the Philosopher declares (Ethic. vii, 7).
Reply to Objection 1. Ignorance in the intellect sometimes precedes the inclination of the appetite and causes it, and then the greater the ignorance, the more does it diminish or entirely excuse the sin, in so far as it renders it involuntary. On the other hand, ignorance in the reason sometimes follows the inclination of the appetite, and then such like ignorance, the greater it is, the graver the sin, because the inclination of the appetite is shown thereby to be greater. Now in both the incontinent and the intemperate man, ignorance arises from the appetite being inclined to something, either by passion, as in the incontinent, or by habit, as in the intemperate. Nevertheless greater ignorance results thus in the intemperate than in the incontinent. On one respect as regards duration, since in the incontinent man this ignorance lasts only while the passion endures, just as an attack of intermittent fever lasts as long as the humor is disturbed: whereas the ignorance of the intemperate man endures without ceasing, on account of the endurance of the habit, wherefore it is likened to phthisis or any chronic disease, as the Philosopher says (Ethic. vii, 8). On another respect the ignorance of the intemperate man is greater as regards the thing ignored. For the ignorance of the incontinent man regards some particular detail of choice (in so far as he deems that he must choose this particular thing now): whereas the intemperate man's ignorance is about the end itself, inasmuch as he judges this thing good, in order that he may follow his desires without being curbed. Hence the Philosopher says (Ethic. vii, 7,8) that "the incontinent man is better than the intemperate, because he retains the best principle [To beltiston, e arche, 'the best thing, i.e. the principle']," to wit, the right estimate of the end.
Reply to Objection 2. Mere knowledge does not suffice to cure the incontinent man, for he needs the inward assistance of grace which quenches concupiscence, besides the application of the external remedy of admonishment and correction, which induce him to begin to resist his desires, so that concupiscence is weakened, as stated above (Question 142, Article 2). By these same means the intemperate man can be cured. But his curing is more difficult, for two reasons. The first is on the part of reason, which is corrupt as regards the estimate of the last end, which holds the same position as the principle in demonstrations. Now it is more difficult to bring back to the truth one who errs as to the principle; and it is the same in practical matters with one who errs in regard to the end. The other reason is on the part of the inclination of the appetite: for in the intemperate man this proceeds from a habit, which is difficult to remove, whereas the inclination of the incontinent man proceeds from a passion, which is more easily suppressed.
Reply to Objection 3. The eagerness of the will, which increases a sin, is greater in the intemperate man than in the incontinent, as explained above. But the eagerness of concupiscence in the sensitive appetite is sometimes greater in the incontinent man, because he does not sin except through vehement concupiscence, whereas the intemperate man sins even through slight concupiscence and sometimes forestalls it. Hence the Philosopher says (Ethic. vii, 7) that we blame more the intemperate man, "because he pursues pleasure without desiring it or with calm," i.e. slight desire. "For what would he have done if he had desired it with passion?"
Source: Summa Theologica (New Advent)