Objection 1. It would seem that euboulia (deliberating well) is not a distinct virtue from prudence. For, according to the Philosopher (Ethic. vi, 5), the "prudent man is, seemingly, one who takes good counsel." Now this belongs to euboulia (deliberating well) as stated above. Therefore euboulia (deliberating well) is not distinct from prudence.
Objection 2. Further, human acts to which human virtues are directed, are specified chiefly by their end, as stated above (I-II, 01, 3; I-II, 18, 4,6). Now euboulia (deliberating well) and prudence are directed to the same end, as stated in Ethic. vi, 9, not indeed to some particular end, but to the common end of all life. Therefore euboulia (deliberating well) is not a distinct virtue from prudence.
Objection 3. Further, in speculative sciences, research and decision belong to the same science. Therefore in like manner these belong to the same virtue in practical matters. Now research belongs to euboulia (deliberating well), while decision belongs to prudence. There euboulia (deliberating well) is not a distinct virtue from prudence.
On the contrary, Prudence is preceptive, according to Ethic. vi, 10. But this does not apply to euboulia (deliberating well). Therefore euboulia (deliberating well) is a distinct virtue from prudence.
I answer that, As stated above (Article 1), virtue is properly directed to an act which it renders good; and consequently virtues must differ according to different acts, especially when there is a different kind of goodness in the acts. For, if various acts contained the same kind of goodness, they would belong to the same virtue: thus the goodness of love, desire and joy depends on the same, wherefore all these belong to the same virtue of charity.
Now acts of the reason that are ordained to action are diverse, nor have they the same kind of goodness: since it is owing to different causes that a man acquires good counsel, good judgment, or good command, inasmuch as these are sometimes separated from one another. Consequently euboulia (deliberating well) which makes man take good counsel must needs be a distinct virtue from prudence, which makes man command well. And since counsel is directed to command as to that which is principal, so euboulia (deliberating well) is directed to prudence as to a principal virtue, without which it would be no virtue at all, even as neither are the moral virtues without prudence, nor the other virtues without charity.
Reply to Objection 1. It belongs to prudence to take good counsel by commanding it, to euboulia (deliberating well) by eliciting it.
Reply to Objection 2. Different acts are directed in different degrees to the one end which is "a good life in general" [Ethic. vi, 5: for counsel comes first, judgment follows, and command comes last. The last named has an immediate relation to the last end: whereas the other two acts are related thereto remotely. Nevertheless these have certain proximate ends of their own, the end of counsel being the discovery of what has to be done, and the end of judgment, certainty. Hence this proves not that euboulia (deliberating well) is not a distinct virtue from prudence, but that it is subordinate thereto, as a secondary to a principal virtue.
Reply to Objection 3. Even in speculative matters the rational science of dialectics, which is directed to research and discovery, is distinct from demonstrative science, which decides the truth.
Source: Summa Theologica (New Advent)