Is there such a thing as an Aristotelian-Thomist tradition? There are a number of philosophers at present who claim to belong to an Aristotelian-Thomist tradition (or A-T), such as Edward Feser, Benedict Ashley, and Charles De Koninck.
It is, of course, true that Aquinas was heavily influenced by Aristotle. Nevertheless, it is not the case that Aristotle and Aquinas were in agreement on all the important fundamentals. Aristotle should not be read as a proto-Thomist, nor Aquinas as a Christian Aristotle. Aquinas sided with the Platonist tradition against Aristotle on some of the most fundamental issues, and Aristotle's own views are often much different than what Thomists make of him.
Aristotle is not a Thomist, Primitive or Otherwise
I'll begin briefly with the mistake of reading Aristotle as a proto-Thomist. It is striking that Aristotle's ousia continues to be referred to as "substance." This is a mistranslation that tends to lead to misunderstanding. Substance etymologically refers to what "stands under" and does not evince the direct relation to being in the manner of ousia. The colloquial notion of "substance" as matter only intensifies this pre-existent problem. Interestingly, earlier Latin translators used "essentia" to translate ousia.
Joseph Owens points out that "[t]he nearest equivalent in the Metaphysics of the notion expressed by 'substance' is 'to hupokeimenon.' This Aristotle calls 'ousia', but states that it is not ousia in the primary sense." (Owens 145.) Thus, Owens concludes, substance, "in its nearest Greek equivalent, [has] been formally rejected by [Aristotle] himself as capable of denoting the primary instance of ousia." 145.
Other examples could be offered. For example, Aristotle rejected a real distinction between being and essence. Or consider Aristotle's cosmological argument: Aristotle does not regard the argument as leading to a transcendent deity, but to a plurality of separate substances. Joseph Owens again illustrates the differences:
Aristotelian metaphysics reasons from the eternity of the cosmic processes and animated heavens to separate and immobile substance as final cause. Whether that separate substance was unique or a plurality seemed a matter of indifference to Aristotle, who left the question to the astronomers to answer, on the basis of the number of original movements they observed in the heavens. ("Aristotle and Aquinas" 39.)
Aristotle's own views are often much stranger than they appear when read through the lens of later thinkers such as Aquinas.
Aquinas often sides with forms of Platonism against Aristotle
St. Thomas often rejects Aristotle's opinions on fundamental issues for various Platonist positions. Let us consider the examples of finitude and perfection, participation, and the limitation of act by potency.
How to think about finitude and infinity goes to the heart of the metaphysical conception of God. For Aristotle, only what is finite and limited can be perfect. (See Phys III.6 207a14; see also On the Genesis of Animals I.1 715b14, Physics III.4-8, Metaphysics K.10.)
St. Thomas rejects Aristotle on this point. Aquinas instead follows the neo-Platonist line of thought, holding that "God Himself is infinite and perfect." (ST I, Q. 7)
As Joseph de Finance observed, "In asking the question, What could limit the One?, Plotinus is implicitly affirming that limitation needs to be justified, and that it can be so only by a degradation of being. The problem is posed and virtually resolved in the same way as St. Thomas." (Etre et Agir 50).
The Limitation of Act by Potency
This is related to another crucial departure St. Thomas takes from Aristotle: the limitation of act by potency.
Many Thomists of the neo-scholastic school were mistaken in thinking that St. Thomas' notion that potency limits act was found in Aristotle. For example, Garrigou-Lagrange states that this principle is found in the first two books of Aristotle's Physics (Reality 43).
But in fact, Aristotle says no such thing, either in the Physics or elsewhere. And this seemed to be apparent to St. Thomas. In his commentaries on Aristotle's works, St. Thomas never mentions potentiality as a limitation on actuality.
W. Norris Clarke's points out that the notion that potentiality limits actuality would not even have made sense in Aristotle's concept, because Aristotle thought of infinity as imperfect. (See Clarke's "The Limitation of Act by Potency".)
Aquinas viewed actuality as infinite, unless limited by potentiality. Aristotle, on the other hand, viewed actuality as finite and limited, as we saw above. The logic of the limitation of act by potency is not only absent from Aristotle, but cannot make sense within his philosophical framework.
On the issue of the limitation of act by potency, Aquinas sides again with the neo-Platonists against Aristotle. Contra Aristotle, for Aquinas, "No act is found limited except by potency."
Participation and the Return to Plato
Aquinas' adoption of the neo-platonic doctrines of infinity and the limitation of act by potency lead to an even more fundamental way that St. Thomas opts for Plato against Aristotle: the doctrine of participation.
Aristotle rejects the doctrine of participation in Metaphysics I.9. Indeed, his rejection of the idea that worldly things participate in the eternal forms could be characterized as central to Aristotle's metaphysics, and the distinction between Platonism and Aristotelianism.
Aquinas, once again, opts for the neo-platonic tradition. As one commentator puts it:
Aquinas shares with Neoplatonism the notion that all beings are essentially unities, and at the same time that no beings in the world are simply identical with their being: whatever does not exist by eternal necessity can exist only by sharing in, i.e., participating in, being, and participation implies a certain difference, or “not,” for one cannot simply be what one has only through participation. There is a difference, Aquinas says, between existence and that which is. A particular being or existing thing cannot be said to be being, but is rather said to “have” it: Ens simpliciter est quod habet esse.
What to make of the "A-T" Tradition?
Is there an A-T tradition? If the A-T tradition is understood to be a fundamental metaphysics shared by Aristotle and St. Thomas, the answer is surely no. St. Thomas, as we have seen, frequently opts for Plotinus as against Aristotle on some of the most fundamental metaphysical questions.
However, we can talk about an A-T tradition in other, more qualified senses. We could refer to those who mistakenly believe that Aristotle and St. Thomas shared the same metaphysics or philosophy of nature as Aristotelian-Thomists, in which case the term would be a pejorative.
However, the term could also refer non-pejoratively to those who emphasize the Aristotelian elements in Aquinas' thought for their own philosophical reasons. There is nothing wrong with such strong readings of Aristotle or Aquinas, so long as it is made clear that it is a strong reading, and therefore not an accurate picture of Aristotle or Aquinas' own views.
W. Norris Clarke, "The Limitation of Act by Potency," New Scholasticism 26 (2) 167-194 (1952).
Joseph de Finance, Etre at Agir (Paris, 1945).
Joseph Owens, The Doctrine of Being in the Aristotelian Metaphysics (3d Ed.).
___________, "Aristotle and Aquinas" in The Cambridge Companion to Aquinas, pp. 38-59. Edited by Norman Kretzmann & Eleanor Stump (1993).
Reginald Garrigou-Lagrange, Reality: A Synthesis of Thomistic Thought (St. Louis, 1950)