Aquinas believes that human reason and good argumentation can get us pretty far. But he is also aware of their limits, as many recent commentators have emphasized. These limits are both natural and the result of sin. Thus, he thinks that grace and the cultivation of intellectual and moral virtue are important in the pursuit of knowledge; they can help us to overcome some (but only some) of these limits. You might say that, on Aquinas’s view, reason as it exists concretely is at its best not when it is “pure reason” but “impure reason.”

The topic of this post has to do with one aspect of “impure reason” in Aquinas. I would like to reflect briefly on the role that authority plays in Aquinas’s epistemology. All Aquinas scholars are familiar with his treatment of this matter in ST, I, 1, 8. The question here is whether sacred doctrine is a matter of argumentation. The following objection is raised:

If [sacred doctrine]  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 replies to this objection thus:

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. Since therefore grace does not destroy nature but perfects it, natural reason should minister to faith as the natural bent of the will ministers to charity. Hence the Apostle says: “Bringing into captivity every understanding unto the obedience of Christ” (2 Cor. 10:5). Hence sacred doctrine makes use also of the authority of philosophers in those questions in which they were able to know the truth by natural reason, as Paul quotes a saying of Aratus: “As some also of your own poets said: For we are also His offspring” (Acts 17:28). Nevertheless, sacred doctrine makes use of these authorities as extrinsic and probable arguments; but properly uses the authority of the canonical Scriptures as an incontrovertible proof, and the authority of the doctors of the Church as one that may properly be used, yet merely as probable. For our faith rests upon the revelation made to the apostles and prophets who wrote the canonical books, and not on the revelations (if any such there are) made to other doctors. Hence Augustine says (Epis. ad Hieron. xix, 1): “Only those books of Scripture which are called canonical have I learned to hold in such honor as to believe their authors have not erred in any way in writing them. But other authors I so read as not to deem everything in their works to be true, merely on account of their having so thought and written, whatever may have been their holiness and learning.”

How might we think about the epistemic value that authority has for Aquinas? What does the above discussion tell us? Here is how Fr. Copleston understands the lesson Aquinas is teaching us here:

Aquinas was the last man to think that philosophical problems can be settled by appeal to great names. “Argument from authority based on human reason is the weakest” (ST, 1a, 1, 8 ad 2). In other words, an argument in favor of a given philosophical or scientific position is the weakest sort of argument when it rests simply on the prestige attaching to the name of an eminent philosopher or scientist. What counts is the intrinsic value of the argument, not the reputation of someone who has sponsored it in the past (Aquinas, 23).

And this is where Fr. Copleston leaves the question. This isn’t a bad reading of Aquinas’s text but, or so I would suggest, there is much more to be said, including some important qualifications to be made.

While Aquinas does say that the argument from authority is the weakest with respect to human reason, it is not weak simply. When it is based on the authority of divine revelation it is the strongest. And let us not forget that Aquinas dignifies sacra doctrina with the title scientia — we are not in the realm of opinion but are dealing with real knowledge. Furthermore, sacra doctrina is the most noble of the sciences and is wisdom beyond all human wisdom.

What is more, as Aquinas notes in his reply, sacra doctrina also makes use of the authority of doctors of the Church and the philosophers. Of course, appealing to them only gets us to the level of probability, but were Aquinas suspicious of the epistemic value of authority and only willing to allow an exception for revelation, we would not expect him to expand the possibilities of legitimate appeal to authority in the field of theology.

But if we put aside the importance that authority has in the science of sacra doctrina and return to its place in the context of human reason, I think we should be careful to observe that in ST, I, 1, 8, ad 2 Aquinas does not dismiss arguments from authority in this context. He says merely that they are the “weakest” of arguments. It is a commonplace in logic that appeals to authority only become fallacious when they are appeals to an illegitimate authority; appeals to legitimate authority are often quite reasonable even if it is rare that they definitively settle a dispute.

Aquinas is aware of and accepts such legitimate appeals to authority in the context of human reason. Not only is this obvious from what he says in the above passage from the Summa but in the De Veritate he suggests that it is reasonable for believers to assent to the truth of what God tells them “since even in dialectical matters there is an argument from authority” (14, 2, ad 9).

But Aquinas is willing to say something stronger than this about the positive role that authority plays in the pursuit of knowledge. Consider these remarks from ST, II-II, 4, 8, ad 2:

Other things being equal sight is more certain than hearing. But if the person from whom we hear greatly surpasses our capacity for understanding [i.e., because of his qualifications, authority on a subject matter], then hearing is more certain than sight. So, one with little knowledge is more certain about what he hears from a man of great knowledge, than about what is apparent to him according to his own reason [Sicut aliquis parvae scientiae magis certificatur de eo quod audit ab aliquo scientissimo quam de eo quod sibi secundum suam rationem videtur.].

This is a striking passage. There are situations, Aquinas thinks, in which I should place more trust in what I am told by another than what I can understand by my own reason. The comparison is probably unfair and anachronistic, but it seems that we are quite far from Descartes’s precept about not taking anything to be true save what I perceive clearly and distinctly with my mind, not to mention Kant’s conception of Aufklärung as daring to think for oneself.

And consider these lines from De Veritate, 14, 10:

To obtain eternal life it is necessary to have faith in those things which are beyond the grasp of reason. We can understand this from what follows. For a thing is brought from imperfection to perfection only through the activity of something perfect. Nor does the imperfect thing at once in the very beginning fully receive the action of that which is perfect; at first it receives it imperfectly and, later, more perfectly. And it continues in this way until it reaches perfection. This is evident in all physical things, which acquire a perfection gradually.

We see the same thing in human works, especially in the learning process. For in the beginning a man has incomplete knowledge, and, if he is to reach the perfection of science, needs an instructor to bring him to that perfection. Nor could the teacher do this unless he himself had full knowledge of the science, that is unless he understood the intelligible principles of the things which form the subject matter of the science. At the outset of his teaching, however, he does not explain to his pupil the intelligible principles of the things to be known which he intends to teach, because then, at the very beginning, the pupil would [have to] know the science perfectly. Instead, the teacher proposes some things, the principles of which the pupil does not understand when first taught, but will know later when he has made some progress in the science. For this reason it is said that the learner must believe. And he could not acquire mastery of the science in any other way unless he accepted without proof those things which he is taught at first and the arguments for which he cannot then understand.

Of course, Aquinas’s discussion of the teacher and the student and the acquisition of a science is made in the context of trying to explain the necessity of faith for attaining eternal life. But obviously Aquinas thinks that his example has to do with what is actually the case in education. I cannot acquire knowledge unless at the beginning I accept some, perhaps many, things on the teacher’s authority. (We don’t need to think of this literally as a teacher with students in a classroom. Books, traditions, can also be the relevant authorities.) This would seem to tell us, then, that in Aquinas’s mind authority does not only have an occasional or marginal function in the pursuit of knowledge but an indispensable function.

Remaining in the sphere of the sciences developed by human reason, we cannot neglect to mention Aquinas’s well-known discussion in ST, I, 1, 2 about certain lower disciplines receiving their principles not from the direct apprehension of these principles by the intellect but from higher disciplines.

Some of the foregoing observations of Aquinas, once we reflect on them, might in the end appear rather pedestrian. Who would deny that authority functions epistemically in the way that he says that it does? I have to admit that I do think that there is something very pedestrian about Aquinas’s comments. And yet we should ask ourselves whether we usually think of Aquinas as holding that authority has a positive part to play not only in sacred doctrine but also in the other sciences. And we might also ask whether Aquinas’s position on authority’s epistemic role jibes well with the view that thinkers like Descartes and Kant take of authority.

Plainly there is much more to be said about all of this but I will have to continue this inquiry another time.

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UPDATE: I developed this post into a paper that I gave at the Pontifical Academy of St. Thomas Aquinas conference in Houston Oct. 19, 2013. Interested readers can find it here.