Objection 1. It seems that liberality is not a virtue. For no virtue is contrary to a natural inclination. Now it is a natural inclination for one to provide for oneself more than for others: and yet it pertains to the liberal man to do the contrary, since, according to the Philosopher (Ethic. iv, 1), "it is the mark of a liberal man not to look to himself, so that he leaves for himself the lesser things." Therefore liberality is not a virtue.
Objection 2. Further, man sustains life by means of riches, and wealth contributes to happiness instrumentally, as stated in Ethic. i, 8. Since, then, every virtue is directed to happiness, it seems that the liberal man is not virtuous, for the Philosopher says of him (Ethic. iv, 1) that "he is inclined neither to receive nor to keep money, but to give it away."
Objection 3. Further, the virtues are connected with one another. But liberality does not seem to be connected with the other virtues: since many are virtuous who cannot be liberal, for they have nothing to give; and many give or spend liberally who are not virtuous otherwise. Therefore liberality is not a virtue.
On the contrary, Ambrose says (De Offic. i) that "the Gospel contains many instances in which a just liberality is inculcated." Now in the Gospel nothing is taught that does not pertain to virtue. Therefore liberality is a virtue.
I answer that, As Augustine says (De Lib. Arb. ii, 19), "it belongs to virtue to use well the things that we can use ill." Now we may use both well and ill, not only the things that are within us, such as the powers and the passions of the soul, but also those that are without, such as the things of this world that are granted us for our livelihood. Wherefore since it belongs to liberality to use these things well, it follows that liberality is a virtue.
Reply to Objection 1. According to Ambrose (Serm. lxiv de Temp.) and Basil (Hom. in Luc. xii, 18) excess of riches is granted by God to some, in order that they may obtain the merit of a good stewardship. But it suffices for one man to have few things. Wherefore the liberal man commendably spends more on others than on himself. Nevertheless we are bound to be more provident for ourselves in spiritual goods, in which each one is able to look after himself in the first place. And yet it does not belong to the liberal man even in temporal things to attend so much to others as to lose sight of himself and those belonging to him. Wherefore Ambrose says (De Offic. i): "It is a commendable liberality not to neglect your relatives if you know them to be in want."
Reply to Objection 2. It does not belong to a liberal man so to give away his riches that nothing is left for his own support, nor the wherewithal to perform those acts of virtue whereby happiness is acquired. Hence the Philosopher says (Ethic. iv, 1) that "the liberal man does not neglect his own, wishing thus to be of help to certain people"; and Ambrose says (De Offic. i) that "Our Lord does not wish a man to pour out his riches all at once, but to dispense them: unless he do as Eliseus did, who slew his oxen and fed the poor, that he might not be bound by any household cares." For this belongs to the state of perfection, of which we shall speak farther on (184,186, 3).
It must be observed, however, that the very act of giving away one's possessions liberally, in so far as it is an act of virtue, is directed to happiness.
Reply to Objection 3. As the Philosopher says (Ethic. iv, 1), "those who spend much on intemperance are not liberal but prodigal"; and likewise whoever spends what he has for the sake of other sins. Hence Ambrose says (De Offic. i): "If you assist to rob others of their possessions, your honesty is not to be commended, nor is your liberality genuine if you give for the sake of boasting rather than of pity." Wherefore those who lack other virtues, though they spend much on certain evil works, are not liberal.
Again, nothing hinders certain people from spending much on good uses, without having the habit of liberality: even as men perform works of other virtues, before having the habit of virtue, though not in the same way as virtuous people, as stated above (I-II, 65, 1). On like manner nothing prevents a virtuous man from being liberal, although he be poor. Hence the Philosopher says (Ethic. iv, 1): "Liberality is proportionate to a man's substance," i.e. his means, "for it consists, not in the quantity given, but in the habit of the giver": and Ambrose says (De Offic. i) that "it is the heart that makes a gift rich or poor, and gives things their value."
Source: Summa Theologica (New Advent)