The following article is an engagement paper originally submitted to IRBS in fulfillment of an assignment for Dr. James Dolezal’s Foundations of Philosophical Theology class.

Contemporary Thomistic studies largely assumes the origins for Thomas’s doctrine “limitation of act by potency” is to be properly and neatly located in Aristotle’s corpus. According to W. Norris Clarke, however, such an assumption is misguided on account of needful language nevertheless absent from Aristotle’s own body of work. If indeed Thomas received limitation of act by potency from Aristotle, one would expect to find such a doctrine in Aristotle’s own words. More significant, perhaps, is the fact that very little substantial change actually took place from the time of the pre-Socratics to the time of Aristotle in the relevant areas according to Clarke.

Norris Clarke’s Brief Observation Concerning Reginald Garrigou-Lagrange’s Assumption

Republished by contemporary scholars, such as Reginald Garrigou-Lagrange, is the common assumption that Thomas received Aristotle’s conception of limitation of act by potency. Yet, to the contrary, Clarke asserts the following, “it is noteworthy that, despite the categorical assertion of Father Garrigou-Lagrange in the above quotation, neither here nor anywhere else in his numerous writings on this doctrine does he ever quote or refer to any precise text where Aristotle himself affirms the limiting role of potency with regard to act.”[1] Contrary to the common assumption mentioned above, the doctrine of limitation of act by potency does not appear in Aristotle. In point of fact, the post-Socratic philosophers appear to conceive of act as limited by its very nature, whilst potency is that which is infinite, or unlimited.

Speaking to Thomas’ own work, Clarke writes, “What is even more decisive, to my mind—and surprising, though I have never seen it reported anywhere—is the fact that throughout the entire extent of St. Thomas’s own commentaries on Aristotle, not excepting that on Book IX of Metaphysics, which deals exclusively with act and potency, there is not a single mention of potency as limiting act nor is there any occurrence of the classic formulas expressing the limitation principle which abound in his independent works.”[2] In other words, though the language of act and potency as categories find a comfortable seat in the Aristotelian corpus, the particular conception of act and potency wherein potency serves as the limiting principle of act is virtually non-existent in spite of Garrigou-Lagrange’s own thesis that, “Aristotle already taught this doctrine.”

Finitude and Infinitude in Anaximander

According to Clarke, “The term infinite (apeiron) first appears in Greek philosophy with the Pre-Socratic Anaximander, who identified it with the primal principle of all things: (1) The Non-Limited is the original material of existing things; further, the source from which existing things derive their existence is also that to which they return at their destruction, according to necessity… (3) This [the Non-Limited] is immortal and indestructible.”[3] Already, the careful reader may catch the identification of the material with the infinite (apeiron). This would appear to imply a like identification of what would eventually come to be known as the “principle of potency” with infinity (since matter must receive form as potency to act).

If it is the case that matter, and thus potency, just are “the infinite,” then conversely, act would necessarily entail limitation. This is why Clarke goes on to say, “[The problem] ‘What is the first principle out of which all things are formed?’ gradually led them—if not Anaximander, at least his successors—to identify the infinite with the indeterminate, formless substratum or raw material of the universe, the primeval chaos of matter in itself, as yet unperfected by the limit of form.”[4] The indeterminate is unlimited because, according to the mind of Anaximander, to determine something is to place limitations upon it. That which is infinite cannot be determined, and that which cannot be determined cannot be perfect. Clark continues, “According to this conception the infinity is identified with the formless, the indeterminate, the unintelligible—in a word, with matter and multiplicity, the principles and imperfection—whereas the finite or limited is identified with the fully formed, the determinate, and there the intelligible—in a word, with number, form, and idea, the principles of perfection.”[5] The infinite, so it is thought, is mutually opposed to perfection, completion, etc.


Plato further develops upon the pre-Socratics by conceiving of what are now termed act and potency as “principles” termed “the limit” and “the unlimited.” Clarke observes the relationship of these two principles in Plato as follows, “According to the Platonic metaphysics, all realities below the supreme idea of the Good (or the One) are a ‘mixture’ of two opposing principles, the limit and the unlimited, which reappear with analogical similarity on all the levels of reality from the world of ideas to the half-real world of sensible things.”[6] Thus, the limit and the unlimited “exist” idealistically and phenomenally, that is, in the world of forms and in the world of “sensible things.” Plato, then, moves the classico-philosophical world toward a more nuanced doctrine of what would eventually come to be known as act and potency. Nevertheless—and this is no surprise, but worth mentioning—the limitation of act by potency doesn’t appear in Plato’s work.

Plato goes on to identify the indeterminate with the “material cause,” or “pure matter.” Clarke observes, “The principle of illumination, on the other hand, is identified with the formlessness and indeterminacy of pure matter and multiplicity as such, and therefore with ‘otherness’ or non-being, as the source of unintelligibility and imperfection.” For Plato, “pure matter” does not appear to serve any sort of limiting purpose at all. To the contrary, that which is indeterminate apparently cannot limit since that which is indeterminate must be infinite, and thus limitless. Therefore, for both the pre-Socratics and Socrates’s greatest student, potency seems to be the least likely candidate in terms of finding a principle of limitation and thus individuation.


Aristotle continues the trend. For this reason, Aristotle cannot rightly be thought of as the progenitor of the Thomistic doctrine of limitation of act by potency. Characterizing Aristotle’s understanding, Clarke points out that, “No complete substance, therefore, can exist as actually infinite. The terms are mutually exclusive. For the perfect, which is but a synonym for the complete or finished, is precisely that which had an end, and the end, he says, is a limit.”[8] Being, then, cannot have an infinite “to be.” For that which is infinite cannot be circumscribed to the parameters of “being” since, if such were the case, the infinite would be determined—a sure and certain absurdity in the eyes of Aristotle.

Summing up his view, Clark recapitulates Aristotle’s own summary, “Nature flees from the infinite, for the infinite is unending or imperfect, and nature ever seeks an end.”[9] Following in the footsteps of Anaximander and Plato, Aristotle does not view what is now called “potency” as a limiting principle. For Aristotle, formless matter (potency) is infinite and thus diametrically opposed to limitation. Nevertheless, according to Clarke, Thomas is still able to appropriate Aristotle along with a major qualification. He writes, “St. Thomas takes over intact this perspective into his own system. But he adds to it another dimension, so to speak, in which the relations are reversed and matter also appears as limiting form.”[10] Whereas Aristotle and his predecessors view matter/potency as the infinite, boundless, and thus, unlimited, Thomas makes matter/potency the “limiting form.”

Further developing his observation of Thomas’s conception, Clarke continues by saying, “Whatever is capable of change of any kind—and only that—must have within it in addition to its present act a principle of potency, or capacity to receive a further act… Act, on the other hand, is always identified with the fully complete, the actually present. Pure act, therefore, is simply a correlative of the immutable, i.e., of pure actualized form, complete in all that is proper to is and incorruptible.”[11] Potency is capacity—a want or lack within a thing—which nevertheless represents what that thing could be. Potency, then, is the limiting principle. Act, contrary to the pre-Socratics, Plato, and Aristotle, is identified with that which is complete or perfect. The only question remaining is, What bridges the gap between Aristotle and Thomas? Is there some other source which may have helped Thomas develop this doctrine of limitation of act by potency?

The Neoplatonism of Plotinus

The Neoplatonism of Plotinus would introduce and apply the metaphysics of the “One” in the baffling equation of infinity and limitation. The “One” would virtually function as a synonym for God, “a synonym for infinite: uncircumscribed (agerigraphos).”[12] Not of little importance, Clarke notes, “The first Christian texts calling God infinite do not appear till the fourth century, and precisely in those circles which are known to have been influenced by Neoplatonism.”[13] 

Neoplatonism casts the discussion of infinite and limited in terms of a higher metaphysic that looks above the formal object of the natural sciences, i.e. the material world. God, the infinite, now stands over and above the created essences, such that, “the old Platonic order or limited, intelligible essences, composed of form as perfecting limit imposed on the infinity of sensible or ‘intelligible’ matter, is still preserved. But their relation to the supreme One by emanation introduces a new dimension of function of the limiting principle, that of limiting what is above it as well as what is below it.”[14] Clarke clarifies thereafter, saying, “In this perspective all the intelligible essences below the One now appear as limited and hence imperfect participations of this supremely perfect and absolutely simple first principle, which somehow embraces within itself the perfection of all the lower determinate essences but is none of them in particular.”[15]

Therefore, with Neoplatonism came the philosophical precursors to a doctrine of limitation of act by potency to an extent not seen in Aristotle or those who came before him. If the “One” is infinite, and if all things below it are finite or limited, yet are by virtue of their imitation or participation in the “One,” that which is (act) is necessarily limited by that which is not but could possibly be (potency).

Concluding with Thomas Aquinas

In light of the above, Thomas reaches his monumental conclusion, “Act is not limited except by reception in a distinct potency.”[16] Such a conclusion, of course, while perhaps influenced negatively by Aristotle and his predecessors, is positively developed in light of the preceding, and more relatively recent, Neoplatonism. Act just is and is limited only by potency. But we must observe with Clarke that this language, however influenced by both Aristotelianism and Neoplatonism, is actually neither properly so called. As Clarke puts it, “The final result of the fusion of the two theories into a single coherent synthesis can thus properly be called neither Aristotelianism nor Neoplatonism. It is something decisively new, which can only be styled, ‘Thomism.’”[17]

The pre-Socratics, Plato, and Aristotle identified what amounts to act with determinacy and finitude. For them, “act” was mutually exclusive to “potency,” as limitation is mutually exclusive to infinity. Neoplatonism, however, saw the “One” as the infinite, created essences being limited and finite. This new relation paved the way for understanding the finite and the infinite in a more coherent way. Thomas understood God to be the infinite, or pure act, creation being composed of act limited by potency.


[1] Clarke, Norris W., Explorations In Metaphysics, (Notre Dame: University of Notre Dame Press, 1994), 67.

[2] Clarke, Explorations In Metaphysics, 68.

[3] Clarke, Explorations In Metaphysics, 69.

[4] Clarke, Explorations In Metaphysics, 69.

[5] Clarke, Explorations In Metaphysics,70.

[6] Clarke, Explorations In Metaphysics, 71.

[7] Clarke, Explorations In Metaphysics, 71.

[8] Clarke, Explorations In Metaphysics, 73.

[9] Clarke, Explorations In Metaphysics, 73.

[10] Clarke, Explorations In Metaphysics, 73.

[11] Clarke, Explorations In Metaphysics, 74.

[12] Clarke, Explorations In Metaphysics, 76.

[13] Clarke, Explorations In Metaphysics, 76.

[14] Clarke, Explorations In Metaphysics, 76. Emphasis added.

[15] Clarke, Explorations In Metaphysics, 76-77.

[16] Clarke, Explorations In Metaphysics, 80.

[17] Clarke, Explorations In Metaphysics, 81.