Any first rule of faith is logically indemonstrable
I dare say one cannot even imagine a foundation of faith against which the same cavils would not be lawful.
Whatever is offered as faith's first rule must be something logically inevident and not properly demonstrable. Theologians and scholastics agree: the principles of faith are inevident and indemonstrable.
Nor can it be proved from other, prior, better-known principles of faith — or it would not be first, and some earlier rule would take its place.
So the first rule of faith, whose authority for us is supreme, cannot be proved by arguments of faith a priori, nor can the questions of irreligious men be met about it by demonstrations and strictly necessary, evident reasons.
Latin
XIX. Imo ausim dicere ne quidem animo fingi posse ullum fidei fundamentum adversus quod non liceat similibus uti cavillationibus. Quicquid enim proferetur tanquam prima fidei regula, necesse est ut sit aliquid logice inevidens, & quod non possit proprie demonstrari. Nam principia fidei, ex communi Theologorum & Scholasticorum consensu, sunt inevidentia & indemonstrabilia. Ac praeterea necesse est ut non possit ex aliis fidei principiis tanquam prioribus & notioribus probari, alioqui prima regula non esset, sed daretur aliqua prior. Unde necessario sequitur primam fidei regulam, cujus authoritas quoad nos suprema est, esse aliquid quod argumentis de fide a priori probari non possit, & super quo etiam non possit satisfieri profanorum hominum quaestionibus per demonstrationes, & rationes prorsus necessarias atque evidentes.