Objection 1. It seems that fortitude is not a special virtue. For it is written (Wisdom 8:7): "She teacheth temperance, and prudence, and justice, and fortitude," where the text has "virtue" for "fortitude." Since then the term "virtue" is common to all virtues, it seems that fortitude is a general virtue.
Objection 2. Further, Ambrose says (De Offic. i): "Fortitude is not lacking in courage, for alone she defends the honor of the virtues and guards their behests. She it is that wages an inexorable war on all vice, undeterred by toil, brave in face of dangers, steeled against pleasures, unyielding to lusts, avoiding covetousness as a deformity that weakens virtue"; and he says the same further on in connection with other vices. Now this cannot apply to any special virtue. Therefore fortitude is not a special virtue.
Objection 3. Further, fortitude would seem to derive its name from firmness. But it belongs to every virtue to stand firm, as stated in Ethic. ii. Therefore fortitude is a general virtue.
On the contrary, Gregory (Moral. xxii) numbers it among the other virtues.
I answer that, As stated above (I-II, 61, 3,4), the term "fortitude" can be taken in two ways. First, as simply denoting a certain firmness of mind, and in this sense it is a general virtue, or rather a condition of every virtue, since as the Philosopher states (Ethic. ii), it is requisite for every virtue to act firmly and immovably. Secondly, fortitude may be taken to denote firmness only in bearing and withstanding those things wherein it is most difficult to be firm, namely in certain grave dangers. Therefore Tully says (Rhet. ii), that "fortitude is deliberate facing of dangers and bearing of toils." On this sense fortitude is reckoned a special virtue, because it has a special matter.
Reply to Objection 1. According to the Philosopher (De Coelo i, 116) the word virtue refers to the extreme limit of a power. Now a natural power is, in one sense, the power of resisting corruptions, and in another sense is a principle of action, as stated in Metaph. v, 17. And since this latter meaning is the more common, the term "virtue," as denoting the extreme limit of such a power, is a common term, for virtue taken in a general sense is nothing else than a habit whereby one acts well. But as denoting the extreme limit of power in the first sense, which sense is more specific, it is applied to a special virtue, namely fortitude, to which it belongs to stand firm against all kinds of assaults.
Reply to Objection 2. Ambrose takes fortitude in a broad sense, as denoting firmness of mind in face of assaults of all kinds. Nevertheless even as a special virtue with a determinate matter, it helps to resist the assaults of all vices. For he that can stand firm in things that are most difficult to bear, is prepared, in consequence, to resist those which are less difficult.
Reply to Objection 3. This objection takes fortitude in the first sense.
Source: Summa Theologica (New Advent)