Objection 1. It seems that the matter of magnificence is not great expenditure. For there are not two virtues about the same matter. But liberality is about expenditure, as stated above (Question 117, Article 2). Therefore magnificence is not about expenditure.
Objection 2. Further, "every magnificent man is liberal" (Ethic. iv, 2). But liberality is about gifts rather than about expenditure. Therefore magnificence also is not chiefly about expenditure, but about gifts.
Objection 3. Further, it belongs to magnificence to produce an external work. But not even great expenditure is always the means of producing an external work, for instance when one spends much in sending presents. Therefore expenditure is not the proper matter of magnificence.
Objection 4. Further, only the rich are capable of great expenditure. But the poor are able to possess all the virtues, since "the virtues do not necessarily require external fortune, but are sufficient for themselves," as Seneca says (De Ira i: De vita beata xvi). Therefore magnificence is not about great expenditure.
On the contrary, The Philosopher says (Ethic. iv, 2) that "magnificence does not extend, like liberality, to all transactions in money, but only to expensive ones, wherein it exceeds liberality in scale." Therefore it is only about great expenditure.
I answer that, As stated above (Article 2), it belongs to magnificence to intend doing some great work. Now for the doing of a great work, proportionate expenditure is necessary, for great works cannot be produced without great expenditure. Hence it belongs to magnificence to spend much in order that some great work may be accomplished in becoming manner. Wherefore the Philosopher says (Ethic. iv, 2) that "a magnificent man will produce a more magnificent work with equal," i.e. proportionate, "expenditure." Now expenditure is the outlay of a sum of money; and a man may be hindered from making that outlay if he love money too much. Hence the matter of magnificence may be said to be both this expenditure itself, which the magnificent man uses to produce a great work, and also the very money which he employs in going to great expense, and as well as the love of money, which love the magnificent man moderates, lest he be hindered from spending much.
Reply to Objection 1. As stated above (Question 129, Article 2), those virtues that are about external things experience a certain difficulty arising from the genus itself of the thing about which the virtue is concerned, and another difficulty besides arising from the greatness of that same thing. Hence the need for two virtues, concerned about money and its use; namely, liberality, which regards the use of money in general, and magnificence, which regards that which is great in the use of money.
Reply to Objection 2. The use of money regards the liberal man in one way and the magnificent man in another. For it regards the liberal man, inasmuch as it proceeds from an ordinate affection in respect of money; wherefore all due use of money (such as gifts and expenditure), the obstacles to which are removed by a moderate love of money, belongs to liberality. But the use of money regards the magnificent man in relation to some great work which has to be produced, and this use is impossible without expenditure or outlay.
Reply to Objection 3. The magnificent man also makes gifts of presents, as stated in Ethic. iv, 2, but not under the aspect of gift, but rather under the aspect of expenditure directed to the production of some work, for instance in order to honor someone, or in order to do something which will reflect honor on the whole state: as when he brings to effect what the whole state is striving for.
Reply to Objection 4. The chief act of virtue is the inward choice, and a virtue may have this without outward fortune: so that even a poor man may be magnificent. But goods of fortune are requisite as instruments to the external acts of virtue: and in this way a poor man cannot accomplish the outward act of magnificence in things that are great simply. Perhaps, however, he may be able to do so in things that are great by comparison to some particular work; which, though little in itself, can nevertheless be done magnificently in proportion to its genus: for little and great are relative terms, as the Philosopher says (De Praedic. Cap. Ad aliquid.).
Source: Summa Theologica (New Advent)