First adversary argument: Scripture cannot prove Scripture, so the Church's testimony must
Their first attempt is to prove that Scripture's authority hangs on the Church's. Scripture, they say, cannot be proved by Scripture. So for the faithful to be sure of Scripture, some divine and infallible testimony must prove it. That testimony, they claim, can only be the Church's — none more certain or august on earth.
If you answer that Scripture in many places asserts its own divinity, they retort that we would already have to be persuaded of that divinity from elsewhere before we could believe the assertion. Mere self-claim is not enough: most of the Apocrypha claimed to be divine and were rightly rejected.
And it seems plain that Scripture cannot prove Scripture, because every proof moves from what is better known — and the same thing cannot be both better and less known than itself. Nothing from Scripture proves anything to someone who does not yet grant Scripture's authority, or who still doubts it.
Latin
II. Primum ergo sic authoritatem Scripturae ab authoritate Ecclesiae pendere, probare conantur. Scriptura, inquiunt, per Scripturam probari non potest. Ergo, ut de Scriptura apud fideles constet, necesse est ut sit testimonium aliquod divinum et infallibile, quo Scriptura probetur. Sed hoc testimonium aliud esse non potest quam Ecclesiae testimonium, quo in terris nullum est certius et augustius. Quod si dicas Scripturam multis in locis se divinam asserere, regerunt illi, ut Scripturae credamus se divinam asserenti, necesse esse ut de illius divinitate jam aliunde persuasi simus. Nec enim, ut scriptum aliquod pro divino habeatur, sufficit ut se divinum afferat: quod fecere libri plerique Apocryphi, qui merito tamen rejecti sunt. Et certe Scripturam per Scripturam ipsam probari non posse inde manifestum videtur, quod probatio omnis est a notioribus. At idem non est seipso notius et ignotius. Neque authoritatem Scripturae nescienti, aut de Scriptura dubitanti ex Scriptura quicquam probatur.