Objection 1. It seems that magnificence is not a virtue. For whoever has one virtue has all the virtues, as stated above (I-II, 65, 1). But one may have the other virtues without having magnificence: because the Philosopher says (Ethic. iv, 2) that "not every liberal man is magnificent." Therefore magnificence is not a virtue.
Objection 2. Further, moral virtue observes the mean, according to Ethic. ii, 6. But magnificence does not seemingly observe the mean, for it exceeds liberality in greatness. Now "great" and "little" are opposed to one another as extremes, the mean of which is "equal," as stated in Metaph. x. Hence magnificence observes not the mean, but the extreme. Therefore it is not a virtue.
Objection 3. Further, no virtue is opposed to a natural inclination, but on the contrary perfects it, as stated above (108, 2;117, 1, Objection 1). Now according to the Philosopher (Ethic. iv, 2) the "magnificent man is not lavish towards himself": and this is opposed to the natural inclination one has to look after oneself. Therefore magnificence is not a virtue.
Objection 4. Further, according to the Philosopher (Ethic. vi, 4) "act is right reason about things to be made." Now magnificence is about things to be made, as its very name denotes [Magnificence= magna facere--i.e. to make great things]. Therefore it is an act rather than a virtue.
On the contrary, Human virtue is a participation of Divine power. But magnificence [virtutis] belongs to Divine power, according to Psalm 47:35: "His magnificence and His power is in the clouds." Therefore magnificence is a virtue.
I answer that, According to De Coelo i, 16, "we speak of virtue in relation to the extreme limit of a thing's power," not as regards the limit of deficiency, but as regards the limit of excess, the very nature of which denotes something great. Wherefore to do something great, whence magnificence takes its name, belongs properly to the very notion of virtue. Hence magnificence denotes a virtue.
Reply to Objection 1. Not every liberal man is magnificent as regards his actions, because he lacks the wherewithal to perform magnificent deeds. Nevertheless every liberal man has the habit of magnificence, either actually or in respect of a proximate disposition thereto, as explained above (129, 3, ad 2), as also (I-II, 65, 1) when we were treating of the connection of virtues.
Reply to Objection 2. It is true that magnificence observes the extreme, if we consider the quantity of the thing done: yet it observes the mean, if we consider the rule of reason, which it neither falls short of nor exceeds, as we have also said of magnanimity (129, 3, ad 1).
Reply to Objection 3. It belongs to magnificence to do something great. But that which regards a man's person is little in comparison with that which regards Divine things, or even the affairs of the community at large. Wherefore the magnificent man does not intend principally to be lavish towards himself, not that he does not seek his own good, but because to do so is not something great. Yet if anything regarding himself admits of greatness, the magnificent man accomplishes it magnificently: for instance, things that are done once, such as a wedding, or the like; or things that are of a lasting nature; thus it belongs to a magnificent man to provide himself with a suitable dwelling, as stated in Ethic. iv.
Reply to Objection 4. As the Philosopher says (Ethic. vi, 5) "there must needs be a virtue of act," i.e. a moral virtue, whereby the appetite is inclined to make good use of the rule of act: and this is what magnificence does. Hence it is not an act but a virtue.
Source: Summa Theologica (New Advent)