Aquinas in an interesting passage in Summa Theologica discusses the question of whether and to what extent one could prove and argue for sacred doctrine, and specifically mentions argument from “authority”. As those who have followed my posts by now, they should be familiar with how the ancients and medievals use the word “authority” to refer to argument from testimony. Here’s the relevant passage:
Article 8. Whether sacred doctrine is a matter of argument?
Objection 2. Further, if it is a matter of argument, the argument is either from authority or from reason. If it is from authority, it seems unbefitting its dignity, for the proof from authority is the weakest form of proof. But if it is from reason, this is unbefitting its end, because, according to Gregory (Hom. 26), “faith has no merit in those things of which human reason brings its own experience.” Therefore sacred doctrine is not a matter of argument.
Aquinas here presents an objection against the idea that sacred doctrine is a matter of argument by positing that arguments from authority is the “weakest form of proof”. As should be clear, if testimonial authority constitutes the weakest evidence, then the entire Christian faith, perilously contingent upon apostolic testimony, would crumble to dust.
Observe very carefully however how he answers the general objection against the idea that sacred doctrine is a matter of argument, and how he carefully qualifies his answer:
I answer that, As other sciences do not argue in proof of their principles, but argue from their principles to demonstrate other truths in these sciences: so this doctrine does not argue in proof of its principles, which are the articles of faith, but from them it goes on to prove something else; as the Apostle from the resurrection of Christ argues in proof of the general resurrection (1 Corinthians 15). However, it is to be borne in mind, in regard to the philosophical sciences, that the inferior sciences neither prove their principles nor dispute with those who deny them, but leave this to a higher science…
Hence Sacred Scripture, since it has no science above itself, can dispute with one who denies its principles only if the opponent admits some at least of the truths obtained through divine revelation; thus we can argue with heretics from texts in Holy Writ, and against those who deny one article of faith, we can argue from another. If our opponent believes nothing of divine revelation, there is no longer any means of proving the articles of faith by reasoning, but only of answering his objections — if he has any — against faith.
The structure of his argument is clear: You can “prove” sacred doctrine only in the sense that you can derive one revealed conclusion, or “article of faith” from another revealed proposition or “article of faith”. The example he uses is how one can engage a heretic who *already* presupposes (!) that the Holy Write contains articles of faith, or someone who merely deny one article of faith, how you can prove him wrong from another article of faith. But you cannot argue someone who doesn’t accept, or presuppose, any divine revelation at all.
As such, in order to demonstrate the Christian faith, you opponent must be someone who already *presupposes* that at least some parts of Scripture already contains divine revelation. But to someone who asks how can you show that Scripture contains any divine revelation in the first place, there’s no argument you can invoke. We can see this a lot clearer by seeing how he answers the specific Objection 2 quoted earlier:
Reply to Objection 2. This doctrine is especially based upon arguments from authority, inasmuch as its principles are obtained by revelation: thus we ought to believe on the authority of those to whom the revelation has been made. Nor does this take away from the dignity of this doctrine, for although the argument from authority based on human reason is the weakest, yet the argument from authority based on divine revelation is the strongest. But sacred doctrine makes use even of human reason, not, indeed, to prove faith (for thereby the merit of faith would come to an end), but to make clear other things that are put forward in this doctrine.
This is a pretty remarkable passage in that it concedes the main thrust of the objection: that arguments from authority based on human reason is the weakest. Arguments from authority only have weight *if* you presuppose that it is based on divine revelation. Thus, in order for you to accept Scriptural authority or testimony, you just have to make an existential leap of faith to believe that it is divine revealed. However, human reason cannot avail to demonstrate that the Scriptures themselves contain divine revelation or have been divinely revealed.
This is a pretty shocking and remarkable passage from Aquinas insofar as it basically concedes the case of the fedora skeptics: no arguments or evidence are available to demonstrate that the Scriptures is a reliable authority or testimony to divine revelation. You just have to “presuppose” that it is divinely reveled otherwise there’s simply nothing to discuss.
The presuppositional flavour of Aquinas would be a lot clearer if one compares it to how Duns Scotus approaches the very same issue. In the Prologue to his Ordinatio, Second Part, he discusses the question of “On the Sufficiency of Revealed Doctrine” and “On the Truth of Sacred Scripture”. Here’s his discussion:
There are on this question innumerable heresies that condemn Sacred Scripture, in whole or in part, as is clear from the books of Augustine and Damascene On Heresies. Some heretics accept nothing of Scripture. Some reject the Old Testament in particular, like the Manicheans, as is clear in Augustine’s book On the Utility of Believing ch.2 n.4, who say that the Old Testament is from the bad principle. Some accept only the Old Testament, like the Jews. Some, like the Saracens, accept something of both, into which impure Mohammed mixed innumerable other impurities. But some accept up to a point what is said in the New Testament, to wit the diverseheretics who, holding for their foundations diverse statements of Scripture badly understood, have neglected others…
Against all these together there are eight ways of rationally convicting them, which are: prophetic foretelling, the agreement of the Scriptures, the authority of the writers, the carefulness of the recipients, the rationality of the contents and the irrationality of the separate errors, the firmness of the Church, the clear evidence of miracles.
Unlike Aquinas who despairs of persuading anyone who simply rejects Scripture in whole or the heretic who “accept nothing of Scripture”, Scotus brimmed with confidence of “rationally convicting them” with arguments, not only from authority, but also more general rational considerations and historical evidence. (His passage here is well worth a read because he anticipates many of the arguments which Evangelical apologetics use to demonstrate the reliability of the Bible.
To make a more general point, we have to remember that when Anselm, once Archbishop of Canterbury and the Father of Scholasticism, first sought to “prove” the faith by reason alone without authority, his predecessor, Lanfranc, was not amused and warned him against that enterprise. Barely a century of scholasticism had passed when testimony went from being the standard method of demonstrating the truths of the Christian faith to it being the “weakest” form of argument and could only be “presupposed” and not demonstrated. They became so intoxicated with their metaphysical systems and their little playgrounds they have made for themselves they forgot how to actually engage the world in evangelism.
As such, perhaps one could say that Aquinas is an evidentialist as far as a mere generic deism or theism is concerned, but as far as the Christian faith is concerned, it is clear that he was a raging presuppositionalist who dismissed the role of reason in demonstrating the divine authority of Scripture and took as it something which one needed to presuppose in order to grasp, not evidence with rational arguments. The contrast with his near contemporary Duns Scotus, could not be clearer.
However, as I’ve already said, the entire Christian faith is contingent upon testimonial authority, if testimonial authority availed nothing, what becomes of the Christian faith? Perhaps it is hardly a surprise that the “High Middle Ages” of Aquinas quickly gave way to the degeneracy and decay of the “Late Middle Ages”. The “Age of Faith” was when weak men guzzled upon the fat of the hard fought victories won by bold missionaries in the “Dark Ages”, or the Early Middle Ages, who wielded miracles and testimony to build Christendom, and they squandered that treasure in pointless idle scholastic speculation.