What's the difference between "media" and "medio" in "virtus in medio stat"?

Question

In Wikipedia's list of Latin phrases, the expression virtus in medio stat is included, with the explanation:

Idiomatically: Good practice lies in the middle path. There is disagreement as to whether "media" or "medio" is correct.

If my deductive reasoning skills have not failed me, the word in question here is medius. In Lewis & Short's definition, I see examples of both in media and in medio, so I'm assuming that Wikipedia's "correct" refers not to rules of grammar but to some "official" origin of the phrase.

Even if that's the case, however, it's not clear to me if there is an actual difference in meaning between the two. So, are both versions grammatically acceptable? If so, are their meanings different, or is it simply a variation in syntax?

Answer 1

The origin of the phrase--or at least the catalyst for its widespread adoption by medieval scholastics--is the Nicomachean Ethics of Aristotle, which in a famous passage defines virtue:

ἔστιν ἄρα ἡ ἀρετὴ ἕξις προαιρετική, ἐν μεσότητι οὖσα τῇ πρὸς ἡμᾶς, ὡρισμένῃ λόγῳ καὶ ᾧ ἂν ὁ φρόνιμος ὁρίσειεν.

Virtue then is a settled disposition of the mind determining the choice of actions and emotions, consisting essentially in the observance of the mean relative to us, this being determined by principle, that is, as the prudent man would determine it.

As already mentioned in a comment, virtus in medio is much more common. It is attested in the works of Thomas Aquinas numerous times:

Praeterea, omnis virtus in medio consistit, ut habetur in II Ethic. (ST II-II Q 146 i arg iii)

You can search the Corpus Thomisticum for "virtus in medio" (unfortunately, the site does not have permalinks) to see many more examples.

Concerning the alternative virtus in media, I would not give much credence to an unsourced Wikipedia article. A Google search for virtus in media does not return a single reference from a Latin text in the first 5 pages. If I were to venture a guess, media probably is meant to refer to the via media.