Laudator Temporis Acti

Augustine, Sermons 133.4 (Patrologia Latina, vol. 38, col. 738; tr. Edmund Hill):

Now let me state very briefly the difference between being mistaken and lying. You are mistaken when you think what you say is true, and it's because you think it's true that you say it. However, if what you say when you are mistaken were true, you wouldn't be mistaken; if it were not only true, but you also knew it to be true, you wouldn't be lying. So you are mistaken, because it's untrue, and you think it's true; you only say it because you think it's true. There is error in human weakness, but there isn't any in a healthy conscience. But if ever you think that what you assert as true is in fact false, then of course you are lying.

Quid autem intersit inter falli et mentiri, breviter dico. Fallitur qui putat verum esse quod dicit, et quia verum putat, ideo dicit. Hoc autem quod dicit qui fallitur, si verum esset, non falleretur: si non solum verum esset, sed etiam verum esse sciret, non mentiretur. Fallitur ergo, quia falsum est, et verum putat; dicit autem nonnisi quia verum putat. Error est in humana infirmitate, sed non est in conscientiae sanitate. Quisquis autem falsum putat esse et pro vero asserit, ipse mentitur.

A good example of differentiae verborum.