Objection 1. It seems that magnificence is not a special virtue. For magnificence would seem to consist in doing something great. But it may belong to any virtue to do something great, if the virtue be great: as in the case of one who has a great virtue of temperance, for he does a great work of temperance. Therefore, magnificence is not a special virtue, but denotes a perfect degree of any virtue.
Objection 2. Further, seemingly that which tends to a thing is the same as that which does it. But it belongs to magnanimity to tend to something great, as stated above (129, 1 and 2). Therefore it belongs to magnanimity likewise to do something great. Therefore magnificence is not a special virtue distinct from magnanimity.
Objection 3. Further, magnificence seems to belong to holiness, for it is written (Exodus 15:11): "Magnificent [Douay: 'glorious'] in holiness," and (Psalm 95:6): "Holiness and magnificence [Douay: 'Majesty'] in His sanctuary." Now holiness is the same as religion, as stated above (Question 81, Article 8). Therefore magnificence is apparently the same as religion. Therefore it is not a special virtue, distinct from the others.
On the contrary, The Philosopher reckons it with other special virtues (Ethic. ii, 7; iv 2).
I answer that, It belongs to magnificence to do [facere] something great, as its name implies [magnificence= magna facere--i.e. to make great things]. Now "facere" may be taken in two ways, in a strict sense, and in a broad sense. Strictly "facere" means to work something in external matter, for instance to make a house, or something of the kind; in a broad sense "facere" is employed to denote any action, whether it passes into external matter, as to burn or cut, or remain in the agent, as to understand or will.
Accordingly if magnificence be taken to denote the doing of something great, the doing [factio] being understood in the strict sense, it is then a special virtue. For the work done is produced by act: in the use of which it is possible to consider a special aspect of goodness, namely that the work produced [factum] by the act is something great, namely in quantity, value, or dignity, and this is what magnificence does. On this way magnificence is a special virtue.
If, on the other hand, magnificence take its name from doing something great, the doing [facere] being understood in a broad sense, it is not a special virtue.
Reply to Objection 1. It belongs to every perfect virtue to do something great in the genus of that virtue, if "doing" [facere] be taken in the broad sense, but not if it be taken strictly, for this is proper to magnificence.
Reply to Objection 2. It belongs to magnanimity not only to tend to something great, but also to do great works in all the virtues, either by making [faciendo], or by any kind of action, as stated in Ethic. iv, 3: yet so that magnanimity, in this respect, regards the sole aspect of great, while the other virtues which, if they be perfect, do something great, direct their principal intention, not to something great, but to that which is proper to each virtue: and the greatness of the thing done is sometimes consequent upon the greatness of the virtue.
On the other hand, it belongs to magnificence not only to do something great, "doing" [facere] being taken in the strict sense, but also to tend with the mind to the doing of great things. Hence Tully says (De Invent. Rhet. ii) that "magnificence is the discussing and administering of great and lofty undertakings, with a certain broad and noble purpose of mind, discussion" referring to the inward intention, and "administration" to the outward accomplishment. Wherefore just as magnanimity intends something great in every matter, it follows that magnificence does the same in every work that can be produced in external matter [factibili].
Reply to Objection 3. The intention of magnificence is the production of a great work. Now works done by men are directed to an end: and no end of human works is so great as the honor of God: wherefore magnificence does a great work especially in reference to the Divine honor. Wherefore the Philosopher says (Ethic. iv, 2) that "the most commendable expenditure is that which is directed to Divine sacrifices": and this is the chief object of magnificence. For this reason magnificence is connected with holiness, since its chief effect is directed to religion or holiness.
Source: Summa Theologica (New Advent)