Saint Aquinas Thomas, Summa Theologica, Part I-II (Pars Prima Secundae…
“ I answer that, Prudence is a virtue most necessary for human life. For a good life consists in good deeds. Now in order to do good deeds, it matters not only what a man does, but also how he does it; to wit, that he do it from right choice and not merely from impulse or passion. And, since choice is about things in reference to the end, rectitude of choice requires two things: namely, the due end, and something suitably ordained to that due end. Now man is suitably directed to his due end by a virtue which perfects the soul in the appetitive part, the object of which is the good and the end. ”
