Objection 1. It seems that patience is not a part of fortitude. For a thing is not part of itself. Now patience is apparently the same as fortitude: because, as stated above (Question 123, Article 6), the proper act of fortitude is to endure; and this belongs also to patience. For it is stated in the Liber Sententiarum Prosperi [The quotation is from St. Gregory, Hom. xxxv in Evang.] that "patience consists in enduring evils inflicted by others." Therefore patience is not a part of fortitude.
Objection 2. Further, fortitude is about fear and daring, as stated above (Question 123, Article 3), and thus it is in the irascible. But patience seems to be about sorrow, and consequently would seem to be in the concupiscible. Therefore patience is not a part of fortitude but of temperance.
Objection 3. Further, the whole cannot be without its part. Therefore if patience is a part of fortitude, there can be no fortitude without patience. Yet sometimes a brave man does not endure evils patiently, but even attacks the person who inflicts the evil. Therefore patience is not a part of fortitude.
On the contrary, Tully (De Invent. Rhet. ii) reckons it a part of fortitude.
I answer that, Patience is a quasi-potential part of fortitude, because it is annexed thereto as secondary to principal virtue. For it belongs to patience "to suffer with an equal mind the evils inflicted by others," as Gregory says in a homily (xxxv in Evang.). Now of those evils that are inflicted by others, foremost and most difficult to endure are those that are connected with the danger of death, and about these evils fortitude is concerned. Hence it is clear that in this matter fortitude has the principal place, and that it lays claim to that which is principal in this matter. Wherefore patience is annexed to fortitude as secondary to principal virtue, for which reason Prosper calls patience brave (Sent. 811).
Reply to Objection 1. It belongs to fortitude to endure, not anything indeed, but that which is most difficult to endure, namely dangers of death: whereas it may pertain to patience to endure any kind of evil.
Reply to Objection 2. The act of fortitude consists not only in holding fast to good against the fear of future dangers, but also in not failing through sorrow or pain occasioned by things present; and it is in the latter respect that patience is akin to fortitude. Yet fortitude is chiefly about fear, which of itself evokes flight which fortitude avoids; while patience is chiefly about sorrow, for a man is said to be patient, not because he does not fly, but because he behaves in a praiseworthy manner by suffering [patiendo] things which hurt him here and now, in such a way as not to be inordinately saddened by them. Hence fortitude is properly in the irascible, while patience is in the concupiscible faculty.
Nor does this hinder patience from being a part of fortitude, because the annexing of virtue to virtue does not regard the subject, but the matter or the form. Nevertheless patience is not to be reckoned a part of temperance, although both are in the concupiscible, because temperance is only about those sorrows that are opposed to pleasures of touch, such as arise through abstinence from pleasures of food and sex: whereas patience is chiefly about sorrows inflicted by other persons. Moreover it belongs to temperance to control these sorrows besides their contrary pleasures: whereas it belongs to patience that a man forsake not the good of virtue on account of such like sorrows, however great they be.
Reply to Objection 3. It may be granted that patience in a certain respect is an integral part of justice, if we consider the fact that a man may patiently endure evils pertaining to dangers of death; and it is from this point of view that the objection argues. Nor is it inconsistent with patience that a man should, when necessary, rise up against the man who inflicts evils on him; for Chrysostom [Homily v. in the Opus Imperfectum, falsely ascribed to St. John Chrysostom] says on Matthew 4:10, "Begone Satan," that "it is praiseworthy to be patient under our own wrongs, but to endure God's wrongs patiently is most wicked": and Augustine says in a letter to Marcellinus (Ep. cxxxviii) that "the precepts of patience are not opposed to the good of the commonwealth, since in order to ensure that good we fight against our enemies." But in so far as patience regards all kinds of evils, it is annexed to fortitude as secondary to principal virtue.
Source: Summa Theologica (New Advent)