Objection 1. It seems that liberality is not about money. For every moral virtue is about operations and passions. Now it is proper to justice to be about operations, as stated in Ethic. v, 1. Therefore, since liberality is a moral virtue, it seems that it is about passions and not about money.
Objection 2. Further, it belongs to a liberal man to make use of any kind of wealth. Now natural riches are more real than artificial riches, according to the Philosopher (Polit. i, 5,6). Therefore liberality is not chiefly about money.
Objection 3. Further, different virtues have different matter, since habits are distinguished by their objects. But external things are the matter of distributive and commutative justice. Therefore they are not the matter of liberality.
On the contrary, The Philosopher says (Ethic. iv, 1) that "liberality seems to be a mean in the matter of money."
I answer that, According to the Philosopher (Ethic. iv, 1) it belongs to the liberal man to part with things. Hence liberality is also called open-handedness [largitas], because that which is open does not withhold things but parts of them. The term "liberality" seems also to allude to this, since when a man quits hold of a thing he frees it [liberat], so to speak, from his keeping and ownership, and shows his mind to be free of attachment thereto. Now those things which are the subject of a man's free-handedness towards others are the goods he possesses, which are denoted by the term "money." Therefore the proper matter of liberality is money.
Reply to Objection 1. As stated above (1, ad 3), liberality depends not on the quantity given, but on the heart of the giver. Now the heart of the giver is disposed according to the passions of love and desire, and consequently those of pleasure and sorrow, towards the things given. Hence the interior passions are the immediate matter of liberality, while exterior money is the object of those same passions.
Reply to Objection 2. As Augustine says in his book De Disciplina Christi (Tract. de divers, i), everything whatsoever man has on earth, and whatsoever he owns, goes by the name of "'pecunia' [money], because in olden times men's possessions consisted entirely of 'pecora' [flocks]." And the Philosopher says (Ethic. iv, 1): "We give the name of money to anything that can be valued in currency."
Reply to Objection 3. Justice establishes equality in external things, but has nothing to do, properly speaking, with the regulation of internal passions: wherefore money is in one way the matter of liberality, and in another way of justice.
Source: Summa Theologica (New Advent)