Objection 1. It would seem that humility is not a virtue. For virtue conveys the notion of a penal evil, according to Psalm 104:18, "They humbled his feet in fetters." Therefore humility is not a virtue.
Objection 2. Further, virtue and vice are mutually opposed. Now humility seemingly denotes a vice, for it is written (Sirach 19:23): "There is one that humbleth himself wickedly." Therefore humility is not a virtue.
Objection 3. Further, no virtue is opposed to another virtue. But humility is apparently opposed to the virtue of magnanimity, which aims at great things, whereas humility shuns them. Therefore it would seem that humility is not a virtue.
Objection 4. Further, virtue is "the disposition of that which is perfect" (Phys. vii, text. 17). But humility seemingly belongs to the imperfect: wherefore it becomes not God to be humble, since He can be subject to none. Therefore it seems that humility is not a virtue.
Objection 5. Further, every moral virtue is about actions and passions, according to Ethic. ii, 3. But humility is not reckoned by the Philosopher among the virtues that are about passions, nor is it comprised under justice which is about actions. Therefore it would seem not to be a virtue.
On the contrary, Origen commenting on Luke 1:48, "He hath regarded the humility of His handmaid," says (Hom. viii in Luc.): "One of the virtues, humility, is particularly commended in Holy Writ; for our Saviour said: 'Learn of Me, because I am meek, and humble of heart.'"
I answer that, As stated above (I-II, 23, 2) when we were treating of the passions, the difficult good has something attractive to the appetite, namely the aspect of good, and likewise something repulsive to the appetite, namely the difficulty of obtaining it. On respect of the former there arises the movement of hope, and in respect of the latter, the movement of despair. Now it has been stated above (I-II, 61, 2) that for those appetitive movements which are a kind of impulse towards an object, there is need of a moderating and restraining moral virtue, while for those which are a kind of recoil, there is need, on the part of the appetite, of a moral virtue to strengthen it and urge it on. Wherefore a twofold virtue is necessary with regard to the difficult good: one, to temper and restrain the mind, lest it tend to high things immoderately; and this belongs to the virtue of humility: and another to strengthen the mind against despair, and urge it on to the pursuit of great things according to right reason; and this is magnanimity. Therefore it is evident that humility is a virtue.
Reply to Objection 1. As Isidore observes (Etym. x), "a humble man is so called because he is, as it were, 'humo acclinis'" [Literally, 'bent to the ground'], i.e. inclined to the lowest place. This may happen in two ways. First, through an extrinsic principle, for instance when one is cast down by another, and thus humility is a punishment. Secondly, through an intrinsic principle: and this may be done sometimes well, for instance when a man, considering his own failings, assumes the lowest place according to his mode: thus Abraham said to the Lord (Genesis 18:27), "I will speak to my Lord, whereas I am dust and ashes." On this way humility is a virtue. Sometimes, however, this may be ill-done, for instance when man, "not understanding his honor, compares himself to senseless beasts, and becomes like to them" (Psalm 48:13).
Reply to Objection 2. As stated (ad 1), humility, in so far as it is a virtue, conveys the notion of a praiseworthy self-abasement to the lowest place. Now this is sometimes done merely as to outward signs and pretense: wherefore this is "false humility," of which Augustine says in a letter (Ep. cxlix) that it is "grievous pride," since to wit, it would seem to aim at excellence of glory. Sometimes, however, this is done by an inward movement of the soul, and in this way, properly speaking, humility is reckoned a virtue, because virtue does not consist in externals, but chiefly in the inward choice of the mind, as the Philosopher states (Ethic. ii, 5).
Reply to Objection 3. Humility restrains the appetite from aiming at great things against right reason: while magnanimity urges the mind to great things in accord with right reason. Hence it is clear that magnanimity is not opposed to humility: indeed they concur in this, that each is according to right reason.
Reply to Objection 4. A thing is said to be perfect in two ways. First absolutely; such a thing contains no defect, neither in its nature nor in respect of anything else, and thus God alone is perfect. To Him humility is fitting, not as regards His Divine nature, but only as regards His assumed nature. Secondly, a thing may be said to be perfect in a restricted sense, for instance in respect of its nature or state or time. Thus a virtuous man is perfect: although in comparison with God his perfection is found wanting, according to the word of Isaiah 40:17, "All nations are before Him as if they had no being at all." On this way humility may be competent to every man.
Reply to Objection 5. The Philosopher intended to treat of virtues as directed to civic life, wherein the subjection of one man to another is defined according to the ordinance of the law, and consequently is a matter of legal justice. But humility, considered as a special virtue, regards chiefly the subjection of man to God, for Whose sake he humbles himself by subjecting himself to others.
Source: Summa Theologica (New Advent)