Reply to the major: what cannot be demonstrated can still be faith's first rule
As for the major — that what is doubtful and uncertain to us of itself cannot be firmly grasped or stand as a sure rule of faith unless a higher authority confirms it — the reply is that this is utterly false if "uncertain to us" means "what cannot be demonstrated and confirmed by wholly necessary arguments."
What cannot be proved by necessary and clear arguments in the philosophical sense can still be firmly believed and be a sure rule of faith, even without confirmation from an authority prior and superior for us.
As we have just shown, the first rule of faith must be something non-evident that cannot be demonstrated — and that neither can nor should be confirmed by a higher authority. Otherwise it would not be, as supposed, faith's first and supreme rule, but only a subordinate, inferior one.
Latin
XXIV. Ad majorem vero illam, Quod ex se nobis est dubium & incertum firma fide non potest apprehendi, & esse certa fidei regula, nisi authoritate superiore confirmetur. Resp. falsissimam esse, si per illud quod nobis est incertum intelligatur id quod demonstrari non potest, & argumentis prorsus necessariis confirmari. Etenim quod probari non potest argumentis, philosophice & proprie loquendo, necessariis & evidentibus, firma tamen fide potest apprehendi, & esse certa fidei regula, quamvis authoritate quoad nos superiori & priori non confirmetur. Imo, ut jamjam probavimus, omnino necesse est ut prima fidei regula sit aliquid inevidens, quod demonstrari non possit, nec tamen superiori authoritate confirmari aut queat aut debeat. Quandoquidem hoc pacto non esset, ut supponitur, prima & suprema fidei regula, sed subalterna tantum & inferior.