I answer that, As stated above (I-II, Q. 61, AA. 3, 4), those virtues are said to be cardinal or principal which have a foremost claim to that which belongs to the virtues in common. And among other conditions of virtue in general one is that it is stated to "act steadfastly," according to Ethic. ii, 4. Now fortitude above all lays claim to praise for steadfastness. Because he that stands firm is so much the more praised, as he is more strongly impelled to fall or recede. Now man is impelled to recede from that which is in accordance with reason, both by the pleasing good and the displeasing evil. But bodily pain impels him more strongly than pleasure. For Augustine says (QQ. 83, qu. 36): "There is none that does not shun pain more than he desires pleasure. For we perceive that even the most untamed beasts are deterred from the greatest pleasures by the fear of pain." And among the pains of the mind and dangers those are mostly feared which lead to death, and it is against them that the brave man stands firm. Therefore fortitude is a cardinal virtue.
Reply Obj. 1: Daring and anger do not cooperate with fortitude in its act of endurance, wherein its steadfastness is chiefly commended: for it is by that act that the brave man curbs fear, which is a principal passion, as stated above (I-II, Q. 25, A. 4).
Reply Obj. 2: Virtue is directed to the good of reason which it behooves to safeguard against the onslaught of evils. And fortitude is directed to evils of the body, as contraries which it withstands, and to the good of reason, as the end, which it intends to safeguard.
Reply Obj. 3: Though dangers of death are of rare occurrence, yet the occasions of those dangers occur frequently, since on account of justice which he pursues, and also on account of other good deeds, man encounters mortal adversaries. _______________________
TWELFTH ARTICLE [II-II, Q. 123, Art. 12]
Whether Fortitude Excels Among All Other Virtues?
Objection 1: It seems that fortitude excels among all other virtues. For Ambrose says (De Offic. i): "Fortitude is higher, so to speak, than the rest."
Obj. 2: Further, virtue is about that which is difficult and good. But fortitude is about most difficult things. Therefore it is the greatest of the virtues.
Obj. 3: Further, the person of a man is more excellent than his possessions. But fortitude is about a man's person, for it is this that a man exposes to the danger of death for the good of virtue: whereas justice and the other moral virtues are about other and external things. Therefore fortitude is the chief of the moral virtues.
Obj. 4: On the contrary, Tully says (De Offic. i): "Justice is the most resplendent of the virtues and gives its name to a good man."