The following is the prepared copy of a paper I delivered on September 15, 2023, at “Aquinas After 750 Years: Still the Common Doctor?” a conference at the Dominican House of Studies.
Despite the observation by Pope Leo XIII that “there is no conflict worthy of the name”[1] between scholastic philosophical principles and the modern natural sciences, the philosophy of nature became “the ‘problem child’”[2] of the Leonine revival of Thomism. While some sought refuge in “the sublime and misty heights of metaphysical abstraction,”[3] others decried the “Thomist cosmology . . . ‘without a cosmos’”[4] that arose in the twentieth century. Today, some wonder whether Thomistic natural philosophy is still relevant.[5] It is still relevant. Indeed, the truth of the “no conflict” thesis from Aeterni Patris is sustained by St. Thomas’s sapiential vision for the philosophy of nature, rooted in his identification of its proper subject, order of inquiry, and intelligible unity.[6] It belongs to the wise to order, and order arises from principles. Aquinas secures a portion of his status as Doctor Communis by handing down the principles that define the discipline of natural philosophical inquiry, which Aquinas also calls physica or scientia naturalis. Let us consider Aquinas’s vision for physics and its proper telos based upon key ideas found in his philosophical commentaries.[7] It is particularly in and through the intelligibility of motion that St. Thomas proposes his sapiential vision for physics.
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To prepare for this conclusion, I propose that we keep in mind the following Thomistic texts. Some are more programmatic; others more akin to logical pressure points.[8]
| [1] | However, I do not say ‘mobile body,’ because it is shown in this book that every mobile is a body; however, no science proves its own subject. And so, straightaway in the beginning of the book On the Heavens, which follows this one, Aristotle begins from the notion of ‘body.’ (In Phys., lib. 1, lect. 1, n. 4) | Non dico autem corpus mobile, quia omne mobile esse corpus probatur in isto libro; nulla autem scientia probat suum subiectum: et ideo statim in principio libri De caelo, qui sequitur ad istum, incipitur a notificatione corporis. |
| [2] | Moreover, the other books of natural science follow upon this book, and in them the species of mobiles are treated . . . . (In Phys., lib. 1, lect. 1, n. 4) | Sequuntur autem ad hunc librum alii libri scientiae naturalis, in quibus tractatur de speciebus mobilium …. |
| [3] | It is wholly impossible to define motion otherwise through those which are prior and more known, unless just as the Philosopher defines it here. (In Phys., lib. 3, lect. 2, n. 3) | Et ideo omnino impossibile est aliter definire motum per priora et notiora, nisi sicut Philosophus hic definit. |
| [4] | For first one determines about the common things of nature in the book of the Physics, in which the mobile insofar as it is mobile is treated. Whence it remains in the other books of natural science to apply these common things to the proper subjects. (In De Caelo, prooem., n. 3) | Nam primo determinantur communia naturae in libro Physicorum, in quo agitur de mobili inquantum est mobile. Unde restat in aliis libris scientiae naturalis huiusmodi communia applicare ad propria subiecta. |
| [5] | Indeed, first [Aristotle] considered the soul in itself [in the De Anima], as if in a certain abstraction . . . (Sent. Lib. de Sensu, prooem., n. 2) | Nam primo quidem consideravit de anima secundum se quasi in quadam abstractione … |
| [6] | … it is manifest that the completeness of science requires that one not stop short among the common things {of natural philosophy}, but proceed all the way to species. (Sent. Meteora, lib. 1, lect. 1, n. 1) | … manifestum est quod complementum scientiae requirit quod non sistatur in communibus, sed procedatur usque ad species. |
| [7] | It is necessary for there to be some speculative science about those things which exist in matter and motion, otherwise the handing down of philosophy, which is the knowledge of being, would not be complete. Yet no other speculative science is about these things, because neither mathematics nor metaphysics [is such]. Therefore, these are the concern of natural science. (Super Boetium de Trinitate, q. 5, a. 2, s.c. 2) | De his, quae sunt in materia et motu oportet esse aliquam scientiam speculativam, alias non esset perfecta traditio philosophiae quae est cognitio entis. Sed nulla alia speculativa scientia est de his, quia neque mathematica nec metaphysica. Ergo est de his naturalis. |
| [8] | … these three modes of contemplation are appointed to the different sciences in diverse ways. For the science of morals, which concerns the ultimate end, possesses the perfection of contemplation; however, the plenitude [of contemplation belongs] to natural science, which considers things proceeding from God; yet metaphysics holds the height of contemplation among the physical sciences. (Super Iohannem, prooem., n. 9) | … diversimode diversae scientiae istos tres modos contemplationis sortiuntur. Perfectionem namque contemplationis habet scientia moralis, quae est de ultimo fine; plenitudinem autem scientia naturalis, quae res a Deo procedentes considerat; altitudinem vero contemplationis inter scientias physicas habet metaphysica. |
Some paraphrasing of these selected texts:
Text [1]: The subject of natural philosophy is mobile being, not mobile body. The reason is that—on pain of begging the question—no science can prove the existence of its own subject, yet Aristotelian physics proves that a moving thing must have three-dimensional extension as a necessarily condition for motion.
Text [2]: The division of the subject of physics arises through a division of the species of mobiles. Now, the principles of this division are the species of motion: e.g., locomotion, alteration, or the motions belonging to living things. In other words, specific physical subjects are not divided by species of bodies.
This importance of motion to the science of physics is emphasized in text [3]. To be ignorant of motion is to be ignorant of nature, for nature is a certain principle and cause of motion. Yet not just any definition of motion will do: Aquinas contends it is “wholly impossible” to define motion in any other way than Aristotle’s.
Text [4]: How does an inquirer progress through the subject-genus of physics? From more general to more specific subjects, considering first what belongs in common to motion and mobile things.[9] To pass from physics in general and into its various, specific domains, the natural philosopher undertakes a certain “application” or “concretion”[10] of the “common things (communia)” to proper subject-matters. Aquinas thinks that such an “application” takes place even within Aristotle’s book the Physics. This is what distinguishes Book VIII from the first seven books.[11]
Text [5]: This progress through the domain of the physical sciences is not necessarily uniform, because each proper subject may require a slightly different approach. For example, the initiation into the study of living things considers the motions and operations of life and in doing so studies their formal cause, the soul, “in a certain abstraction.” The “abstraction” is of a peculiar sort because it focuses upon a part (the soul) more than the whole to which that part belongs (viz., the living thing). This is still methodically sound insofar as we begin with what is better known to us, the experiential immediacy of being alive.[12]
Text [6]: The progression of physical inquiry through the natural sciences has a teleological unity. This is the goal-state of its inquiries, namely, a specific understanding of the very natures of mobile beings. The goal of physics is to know the principles, causes, and elements of all mobile beings in their causal concretion, both proximately and ultimately.
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With these in mind, St. Thomas’s sapiential vision for physics takes special note of principles of the subject, progression, and unity of physics. The subject of physics is ens mobile. It is not mobile body, corpus mobile, as St. Albertus thought, because corporeality is a property of the subject of physics. Neither is the subject material things, nor is it natural beings or hylomorphic substances, because materiality or nature or matter-and-form name causes of the subject of physics. Just as the subject of moral philosophy is human action, which subject is illuminated by the principles and causes of those actions, so too the subject of physics is being qua mobile, which subject is explained through natural principles and causes.[13]
The progression in our knowledge towards the principles, causes, and elements of mobile being is of a sort which Aquinas emphasizes and follows frequently as a teacher. We proceed from what is better known to us towards what is better known in itself; this is to proceed from potentially grasping the causality behind motion to actually doing so; actually doing so requires that we proceed from more common and generic concepts to more specific ones, the reason being that the more specific concept is the more actual in its logical intension. This progression is not achieved via a sequence of demonstrations. Rather—and rather importantly—this progression is one determined by a constant return to mobile beings as the measures of natural philosophy’s intellectual maturity.[14]
This progression is teleologically unified in what the natural philosopher seeks to know most of all, regardless of the conceptual or technical means deployed towards that end. No doubt St. Thomas would have been amazed at the characteristics of the universal background radiation as a clue to the cosmos’s physical origins, yet he would not be surprised that the mathematical models used to interpret this phenomenon are subordinated to the natural philosopher’s end of knowing the cosmos’s physical unity of order and not some mathematical simulacra of order. The very species of things in their most proximate accounts and the universal causality uniting them—both agent, formal, and especially final—is the telos of a long road of inquiry that begins with wondering what motion is and how it is possible.
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Indeed, St. Thomas especially proposes his sapiential vision for physics in and through the intelligibility of motion, the reason being that investigating motion is the way to naturally articulate the subject-genus of physics. It is also the natural way in which we come to know what is. Why? Because those ignorant of motions are ignorant of natures.[15] Motion is the entryway into understanding the natures of things. This can be indicated in two ways.
The first way in which motion is an entryway is that motion as an intelligible reality leads us to the subject of natural philosophy. The account of motion’s reality solves the first problem in natural philosophy, steering the physicist between Parmenidean stasis, Heraclitean flux, and other difficulties.[16] That is, either motion is a reality or not. If it is not a reality, then it exists only in opinion or appearance. Yet if motion is a reality, then either it is a reality distinct from both rest as well as the thing in motion or not. Some philosophers say motion is not distinct from rest or the thing in motion (for instance, the “at–at” view of motion). Others maintain that motion is a distinct actuality. Among these, some say that motion requires no definition, because it is so clearly imaginable or (at least) measurable. Others think that motion can be defined. Of these, some maintain that motion can only be defined through contradictory notions or those which—on closer inspection—are posterior to motion (for example, defining motion using time). Yet Aristotle and Aquinas maintain that motion is a distinct reality and that it is definable non-circularly through principles prior to motion: act and potency. Indeed, who else has succeeded at all in defining the reality of motion? The natural philosopher is forced by the truth about motion to distinguish between act and potency. The natural world is given very different accounts as a consequence of what one makes of motion. Such a disparity among accounts of the world of change shows the difference between a field and a discipline, between a dialectical versus a scientific grasp of some subject.[17] Another example: Happiness is known to the entire dialectical field of those in Ethics, I.4–6, but the disciplined study of happiness is established in Ethics, I.7–8 and I.13 (at least). Natural philosophy begins dialectically, but these are the Socratic plains and aporetic foothills lying before the heights of scientific discipline.
A second way in which motion is an entryway is that motion is the intelligible means that draws the physicist on to explore his subject-matter. Here, the structure and specific distinction of natural bodies is necessary but not sufficient. Besides, these differences are revealed through motion. Again, a focus on motion helps the natural philosopher to avoid totally mathematizing his object of concern. What is in motion acts upon us and is acted upon in turn; the intelligibility of the world of change is not subject to our control and does not readily reveal itself. This is unlike mathematical models of nature which we can conceptually manipulate in clear, distinct, and freely chosen ways. Lastly, the intelligibility of the world subject to change is not certified in the last step of a meditative process or aprioristic deduction. Rather, it is naturally hoped for as the first step. Motion is the intelligible means that draws the physicist on towards the telos of physics.
What’s more, motion serves as an analogue through which one may compare, contrast, and lead others to discover truths about what may appear to be mere motions but either are not or are not quite entirely so. Non-living motions are contrasted with the self-determining motions and operations of living things. Sensation as such is not a motion. Physical changes are concomitant to emotions—the passions of the soul—but do not exhaust their reality. To think about or work though an argument or to reach an insight are not motions. And, of course, creatio non est mutatio. To make such points, St. Thomas engages in extensive contrasts to the intelligible structure of motion, mobile beings, and movers.
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Such, in outline, is St. Thomas’s sapiential vision for natural philosophy. Should St. Albertus Magnus and Aristotle receive more credit? Well, St. Albertus’s vision is rather the vision of a natural philosopher. Indeed, Aquinas corrects his teacher concerning the subject of physics. [18] Furthermore, that St. Thomas was an excellent student of Aristotle does not detract from his abilities as a teacher in this regard. Sine Thoma, mutus Aristoteles.[19] Originality for its own sake is not a necessary condition of a great teacher.
Again, St. Thomas’s sapiential vision for natural philosophy might seem irrelevant to the modern natural sciences. Yet Aquinas’s principles lead us beyond the imagination’s grasp through to the intelligibility of motion. They allow for natural philosophical insight within our contemporary natural sciences. Think of recent Thomistic work on the character of physical fields, potential and kinetic energy, or quantum theory.[20]
Lastly, it may appear redundant to highlight natural philosophy on its own as part of Aquinas’s sapiential vision, since some Thomists and other neo-scholastics for over a hundred years have reduced natural philosophy to a part of metaphysics.[21] This view and arguments for it are wrong in many ways. For now, note that Aquinas disagrees with the view. He maintains that the philosophy of nature is necessary to complete the “handing down” of philosophy: [7] “It is necessary for there to be some speculative science about those things which exist in matter and motion, otherwise the teaching of philosophy, which is the knowledge of being, would not be complete. Yet no other speculative science is about these things, because neither mathematics nor metaphysics [is such]. Therefore, these things are the concern of natural science.”[22]
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Some think that to begin the life of the mind with generic and vague concepts is both erroneous and a human imperfection. Others maintain that to begin with the most generic conceptions of things is not only correct, but such is the perfection of reason. Aquinas, following Aristotle, disagrees with both. Instead, the humble intellectual beginnings of the natural philosopher in the generic and vague grasp of mobile being is not an error, yet neither is such a grasp the completion of physical contemplation.[23] As natural philosophy comes into its own, following Aquinas’s architectonic directions, it achieves a certain plenitude in its contemplation. This sets it apart from both practical philosophy and metaphysics. Considering three modes of perfection belonging to these three parts of philosophy, Aquinas teaches [8]: “These three modes of contemplation are appointed to the different sciences in diverse ways. For the science of morals, which concerns the ultimate end, possesses the perfection of contemplation; however, the plenitude [of contemplation belongs] to natural science, which considers things proceeding from God; yet metaphysics holds the height of contemplation among the physical sciences.”[24] For the sake of attaining such heights— and, indeed, ones higher still—the Doctor communis proposes his sapiential vision for natural philosophy.
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Endnotes
[1] Pope Leo XIII, Encyclical Aeterni Patris, n. 30; translation from the Vatican website.
[2] E. J. E. Hüffer, S.J., a contemporary of Petrus Hoenen, S.J., cited in Abraham C. Flipse, “Between Neo-Thomist Natural Philosophy and Secular Science: Roman Catholic Scientists in the Netherlands, 1900–1950” Proceeding of the Third International Conference of the European Society for the History of Science 2009 (2010): 1149.
[3] James A. Weisheipl, O.P., “Commentary on Boyle,” in V. B. Brezik, C.S.B, ed., One Hundred Years of Thomism: Aeterni Patris and Afterwards, A Symposium (Houston: Center for Thomistic Studies, UST, 1981), at 27, citing John Gmeiner’s Mediaeval and Modern Cosmology (Milwaukee: Hoffman Brothers, Co., 1891), 16.
[4] William A. Wallace, O.P., “Thomism and Modern Science: Relationships Past, Present, and Future,” The Thomist 32, no. 1 (1968): 67–83, at 77. He borrows the phrase from Raymond J. Nogar, O.P., “Cosmology Without a Cosmos,” in From an Abundant Spring: The Walter Farrell Memorial Volume of The Thomist, ed. by The Staff of the Thomist, 363–92 (New York: P.J. Kenedy & Sons, 1952), 363.
[5] See Daniel D. De Haan, “Is Philosophy of Nature Irrelevant?” Proc. ACPA 93 (2019): 327–48.
[6] These three are loci classici for the commentatorial tradition; see John of St. Thomas, O.P., Cursus Philosophicus Thomisticus, vol. 2, ed. B. Reiser, 2nd ed. (Taurini: Marietti, 1948), 6–33 (q. 1, aa. 1–3).
[7] These three are also loci classici for the commentatorial tradition; see John of St. Thomas, O.P., Cursus Philosophicus Thomisticus, vol. 2, ed. B. Reiser, 2nd ed. (Taurini: Marietti, 1948), 6–33 (q. 1, aa. 1–3). The complete version of such a survey of Aquinas’s prooemia is found in Jean-Baptiste Échivard, Une introduction a la philosophie: Les proemes des lectures de saint Thomas d’Aquin aux oeuvres principales d’Aristote, 5 vols. (Paris: François-Xavier de Guibert, 2004–2008), which continues lines of thought from Charles De Koninck.
[8] All of these texts are on the accompanying handout.
[9] St. Thomas, Sent. Lib. de Sensu, prooem., n. 2: “And just as different genera of sciences are distinguished according to this, that things are separable from matter in diverse ways, so too in the individual sciences and above all in natural sciences are the parts of the science distinguished according to different modes of separation and concretion. And because universals are more separate from matter, therefore in natural science one proceeds from the more universal to the less universal, as the Philosopher teaches in Physics, Book I. Whence also natural science begins the handing on [of its subject] from those which are the most common to all natural things—which are motion and the principles of motion—and from thence it proceeds by way of the concretion or the application of common principles to certain determinate mobiles, of which certain ones are living bodies.”
[10] See the quote in the preceding note.
[11] See St. Thomas, In Phys., lib. 8, lect. 1, n. 967: “In praecedentibus enim libris Aristoteles locutus fuerat de motu in communi, non applicando ad res: nunc autem inquirens an motus semper fuerit, applicat communem considerationem motus ad esse quod habet in rebus.”
[12] Here, and elsewhere, the influence of Charles De Koninck should be noted. See his Oeuvres de Charles de Koninck, tt. I-1 and I-2 (Québec: Presses de l’Université Laval, 2009 and 2012), as well as The Writings of Charles De Koninck: Volumes One and Two, ed. and trans. by R. McInerny (Notre Dame, IN: University of Notre Dame Press, 2008 and 2009). His essays on the study of the soul, abstraction from matter, and the unity and diversity of the natural sciences are key contributions to this area.
[13] This is the converse of what St. Thomas takes to be a better known order: Sent. Ethic., lib. 1, lect. 1, n. 3: “Sicut igitur subiectum philosophiae naturalis est motus vel res mobilis, ita etiam subiectum moralis philosophiae est operatio humana ordinata in finem vel etiam homo prout est voluntarie agens propter finem.”
[14] See St. Thomas, In Phys., lib. 1, lect. 1, as well as De Koninck’s essay on the study of the soul.
[15] St. Thomas, In Phys., lib. 3, lect. 1, n. 276: “Cum ergo nos intendamus tradere scientiam de natura, necesse est notificare motum.”
[16] This division follows Marcus R. Berquist, “A Summary of Different Views about Motion and How It Is to be Defined,” in Learning and Discipleship: The Collected Papers of Marcus R. Berquist (Santa Paula, CA: Thomas Aquinas College, 2019), 392–97.
[17] This distinction between a field and a discipline is made by Umberto Eco, A Theory of Semiotics (Bloomington, IN: Indiana University Press, 1978), 7. St. Thomas has a kindred distinction between a science’s dialectical mode of proceeding rationabiliter and its mode of proceeding rationabiliter; see SBdT, q. 6, a. 1, c. (a).
[18] Also, the places where Aquinas disagrees with his teacher, including the point at issue about ens mobile, are instructive. See Steven Baldner, “Albertus Magnus and the Categorization of Motion,” The Thomist 70, no. 2 (2006): 203–35, and Benedict M. Ashley, O.P., “St. Albert and the Nature of Natural Science,” in Albertus Magnus and the Sciences: Commemorative Essays, ed. by J. A. Weisheipl, 73–102 (Toronto: Pontifical Institute of Mediaeval Studies, 1980).
[19] See Petrus Hoenen, Cosmologia, 5th ed. (Roma: Universitas Gregoriana, 1956), 305: “The theory of Aristotle was perfectly understood by St. Thomas, to the point that he makes use of the clearest formulations even in the most remote deductions. Aquinas seems to have been the first one who fully understood the Stagirite; after so many ages, at last someone was found equal to the talent of Aristotle’s mind, such that through his clarity we too even now can easily understand the problem of the greatest import and the one most worth of metaphysical attentiveness: how a being is able to be intrinsically mutable.” Translation mine.
[20] On the formal object see St. Thomas, ST IIa-IIae, q. 1, a. 1, c., and Exp. Po. An., lib. 1, lect. 41. On physical fields, see, Christopher A. Decaen, “The Impossibility of Action at a Distance,” in Wisdom’s Apprentice: Thomistic Essays in Honor of Lawrence Dewan, O.P., ed. by P. A. Kwasniewski, 173–200 (Washington, D.C: Catholic University of America Press, 2007); concerning energy, see Thomas J. McLaughlin, “Act, Potency, and Energy,” The Thomist 75 (2011): 207–43, and “Energy and Form,” The Thomist 86, no. 1 (2022): 1–51; and about quantum continua, see Robert C. Koons, Is St. Thomas’s Aristotelian Philosophy of Nature Obsolete? (South Bend, IN: St. Augustine’s Press, 2022).
[21] See St. Thomas, Sent. Ethic., lib. I, lect. 1, n. 2, quoted above, n7; Pope Leo XIII’s own n. 30 in Aeterni Patris, cited above, n1, could be read as support for this objection. This position is held by Edward Feser, in Aristotle’s Revenge: The Metaphysical Foundations of Physical and Biological Science (Neunkirchen-Seelscheid: Editiones Scholasticae, 2019), but its lineage is far less recent: see sources cited by Feser, ibid., 5–9, and other, older ones in Filippo Selvaggi, Cosmologia, (Romae: Universitatis Gregorianae, 1959), 6–11.
[22] See Super Boetium de Trinitate, q. 5, a. 2, s.c. 2: “De his, quae sunt in materia et motu oportet esse aliquam scientiam speculativam, alias non esset perfecta traditio philosophiae quae est cognitio entis. Sed nulla alia speculativa scientia est de his, quia neque mathematica nec metaphysica. Ergo est de his naturalis.”
[23] See Yvan Pelletier, “La connaissance confuse, principe et fondement permanent du bien achevé de l’intelligence speculative,” Ph.D. Dissertation, Université Laval (Québec), 1974.
[24] See Super Iohannem, prooem., n. 9.
John G. Brungardt 