The following is an excerpt from a paper I recently presented at a conference titled Saint Thomas d'Aquin et ses sources arabes / Aquinas and the Arabs at the Sorbonne in Paris (which is, coincidentally, the modern successor institution of the medieval University of Paris, where St. Thomas taught). The title of the paper was: "Averroes and Aquinas on the Dialectical Nature of Revealed Theology."
Two of the greatest Aristotelian commentators, Averroes and Aquinas, used the Aristotelian distinction between demonstrative, dialectical, and rhetorical discourses to assign an epistemological status to religious or theological knowledge, that is, to conclusions drawn from revelation. But their respective views on this point turned out to be very different, even opposite. Averroes considered religious knowledge to be dialectical in nature, whereas Aquinas believed revealed Christian theology to be a demonstrative science. The author shows that both of these greater Aristotelian commentators strive, although very differently, to be faithful to Aristotle concerning the epistemological status of theology. Ultimately, however, their approaches converge, particularly insofar as in both accounts, theology is dialectical in nature, at least in a qualified sense in the case of Aquinas.
As is well known, at the beginning of the Summa theologiae, Aquinas faces the objection that sacra doctrina cannot be a science, because it assumes the articles of faith as its principles:
It seems that sacred doctrine is not a science. For every science proceeds from principles known per se. But sacred doctrine proceeds from articles of faith, which are not known per se, since they are not admitted by all: “For faith does not belong to all,” as is said in 2 Thessalonians 3 [v. 2]. Therefore sacred doctrine is not a science. (ST I.1.2 arg. 1)
What is at issue here is that, as Aristotle says, the demonstrative sciences “proceed from premises which are true, primary, immediate, better known than, prior to, and causative of the conclusion” (Aristotle, Posterior Analytics, 71b20-23). Or, as we read in the Topics,
[Reasoning] is a ‘demonstration’, when the premises from which the reasoning starts are true and primary, or are such that our knowledge of them has originally come through premises which are primary and true.... Things are ‘true’ and ‘primary’ which are believed on the strength of nothing else but themselves: for in regard to the first principles of science it is improper to ask any further for the why and wherefore of them; each of the first principles should command belief in and by itself (Aristotle, Topics 1.1)
Therefore, it would seem that sacra doctrina falls short of being a science, because it does not proceed from primary or per se known principles, but from premises that must be accepted on faith, without any evidence. Aquinas replies by citing the well-known Aristotelian doctrine of the subalternation of sciences: “The principles of any science are either per se known, or are reduced to the awareness of a higher science. And such are the principles of sacred doctrine....” (ST I.1.2 ad 1). The body of the article is more explicit:
We must bear in mind that there are two kinds of science. There are some which proceed from a principle known by the natural light of intelligence, such as arithmetic and geometry and the like. There are others which proceed from principles known by the light of a higher science: thus the science of optics proceeds from principles established by geometry, and music from principles established by arithmetic. (ST I.1.2c)
That is to say, whereas some sciences proceed from per se known principles, others ‘believe’ (credunt) or ‘presuppose’ (supponunt) their principles as having been demonstrated by more fundamental sciences, as optics accepts its principles as having been demonstrated by geometry.
In other texts, Aquinas gives the name of ‘subaltern sciences’ to those inferior sciences that accept their principles as having been proven by others, and ‘subalterning sciences’ to the superior sciences that prove the principles of the subaltern sciences. In the prologue to the Sentences commentary, for instance, Aquinas inserts a ‘rectification’—regarding which I shall say more below—where he tells us that:
Superior sciences proceed from per se known principles, as geometry and the like, which have per se known principles, such as ‘if you add equals to equals...’, etc. But inferior sciences, which are subaltern to superior sciences, do not proceed from per se known principles, but presuppose conclusions proven in superior sciences and use them as principles, which in truth are not per se known principles, but are proven through per se known principles in the superior sciences: as optics, which deals with the visible line, is subaltern to geometry, from which it presupposes those things which are proven concerning the line insofar as it is a line, and through them, as through its principles, proves conclusions concerning the line insofar as it is visible (Sent., prol., q. 1, a. 3, qc. 2).
Sacra doctrina, he concludes, is like optics, in that it is subaltern to a more fundamental science, namely, the science possessed by God.
So it is that sacred doctrine is a science because it proceeds from principles established by the light of a higher science, namely, the science of God and the blessed. Hence, just as the musician accepts on authority the principles taught him by the mathematician, so sacred science is established on principles revealed by God (ST I.1.2c).
Thus goes the oft-rehearsed, seldom-contested story of Aquinas’ account of the scientific nature of sacra doctrina. [...] Yet in order to place sacra doctrina on solid demonstrative footing, St. Thomas would have to demonstrate that the articles of faith are per se known to God, and hence demonstrate that they are true. Yet he cannot do so; he clearly accepts their truth on faith, and not on demonstration. Thus, he ultimately grounds his claim concerning the scientific nature of theology on a belief in the fact of revelation. Therefore, by appealing to God’s knowledge of the articles of faith as the ultimate justification of the scientific character of sacra doctrina, Thomas never fully avoids Averroes’ view that religious knowledge is somehow dialectical, as a discipline that proceeds from probable propositions, and not from per se known truths. And what is most surprising is that Aquinas acknowledges as much! In his De veritate, he tells us that sacra doctrina “does not attain to the perfect ratio of science” (non perfecte attingit ad rationem sciendi).
He who has a subaltern science does not perfectly attain to the ratio of science, except insofar as his knowledge is somehow continuous with the knowledge of him who has the subalterning science. Nonetheless, the inferior knower is not said to have science concerning those things that he presupposes, but concerning the conclusions that are necessarily concluded from the presupposed principles. And thus even the faithful can be said to have science concerning those things which are concluded from the articles of faith (De veritate, q. 14 a. 9 ad 3).
Thus, the practitioner of a subaltern science must believe the principles of that science, often without knowing how a higher science can prove them. For instance, take a practitioner of optics that does not master geometry; such a person would indeed possess the science of optics, but only imperfectly. Similarly, Aquinas teaches that, in this life, practitioners of sacra doctrina must believe or presuppose its principles; they cannot know the science that God has of Himself, and to which sacra doctrina is subaltern, and therefore, sacra doctrina in this life “does not attain to the perfect ratio of science.” Hence, Aquinas himself is acknowledging that sacra doctrina is not quite a science, at least not quoad nos, for it is possessed by us but imperfectly. Thus it cannot be univocally called a ‘science’, in the same sense in which this term is predicated of the other human sciences, which proceed from principles that are per se known quoad nos. Rather, sacra doctrina is a science only equivocally—or as has been recently argued, it is a science only analogically.
Now, if I am allowed to extend the analogy a bit, note also that the practitioner of optics does not blindly believe in the geometrical principles of optics, and does not believe them simply because he wants to believe them, but believes them on the basis of a practical judgment of their credentitas (the fact that they are to be believed); that is, those principles are believed ultimately because the practical necessity of believing them can be 'seen', that is, known scientifically (as opposed to believed). The practitioner of optics, then, believes the principles of optics, but scientifically knows their credentitas. The optician knows that those principles are in themselves justified, but in himself they are not justified; the optician does not know how they are justified because he does not possess the science of geometry. Similarly, Aquinas will be careful to argue that the principles of theology can be known to be justified in se, and that the imperfection of sacra doctrina is only quoad nos. This imperfection does not imply a defect in the objective justification of sacra doctrina, just as the optician’s belief in the (geometrical) principles of optics is in itself justified, but may be unjustified subjectively in the mind of the optician, and the latter imperfection does not imply a defect in the objective justification of optics. Only the intellect that possesses both the science of optics and that of geometry can be said to attain to the perfect scientific or demonstrative ratio of optics. Thus, we could say that, for Aquinas, theology is a science in se, but dialectical quoad nos, for in us it is only imperfectly a science: “These principles are above reason and thus human reason cannot grasp them perfectly: And thus a certain defective knowledge occurs, not from a defect in the certitude of those things known, but from a defect on the part of the knower” (Super Sent. Prol., q. 1, art. 3, ad 3). But Aquinas hopes that this deficiency will be remedied in the next life:
The terminus of principles naturally known are comprehensible to our intellect: therefore, the knowledge that arises from those principles is a certain vision: but it is not thus with the terminus of the articles [of faith]. Hence, in the future life, when God will be seen through His essence, the articles will be thus seen and known per se, as now the principles of demonstration [are seen and known per se] (Super Sent., lib. 3, d. 24, q. 1, a. 2, qc. 1, ad 2).
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