In Q: How do we know that the correspondence of Seneca and St. Paul was a forgery? Brian, in a comment, gave this quote:
"nec enim hoc diceres, censor sophista magister tanti principis etiam omnium, nisi quia vere dicis,";
"For you would not say this, censor sophist, teacher of such a great prince and, even, of all, unless you spoke the truth,".
It reads like a conditional sentence using "nisi" instead of "si": "unless you speak the truth....you would not say this". In the protasis clause, what is the role of "quia" = "because"; "unless because you speak the truth"?! It doesn't work in the English, what is happening in the Latin? What if "quia" was omitted?