The Nature of Habit and a Human Measure for AI (Part 1)
The present essay and its other half were given as talks in the Czech Republic in 2026, as part of a pedagogical gathering, hosted by the Slovak Dominicans, on the Human Person and AI. These pieces must be read together. For the present gathering, my tone is pedagogical. A more technical version of this paper, focusing primarily on the AI questions (and presupposing much of the philosophical underpinning) will be posted in September of 2026 when I present this more technical talk for the Lyceum Institute later this year, at their conference, “Human Formation in the Digital Age.” The abstract for that paper is as follows:
The question of technology always contains within it a further question: “What is the scale of the human?” Technology is not superhuman, for it represents one of the spiritual perfections of man the practical knower. Nonetheless, like all things spiritual in man, it contains the seeds of something supra-embodied, something potentially infinitized. That is, it carries within it the siren song of the transhumanist. In establishing measures for the virtuous use of human tools, then, the question of the scale of the human is of central importance—yet that scale is itself manifold. This talk considers one dimension of it: how a solid account of habitus can articulate the measure of technology, showing that technology must be well-ordered within the human reality of habituation and the vital, internal ordering of the human person.
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The term "habit" is subject to a small amount of ambiguity, at least in the Western European languages. Very often it conjures up the idea of rote activity—repetitive and thoughtless patterns of acting. We might say that I have the habit of tapping my finger on the desk while thinking, or that I habitually sit to the right when I get on a ski lift. In any event, the notion of habit seems to indicate something rather deterministic and unintelligent.
How surprising it is, then, to find a central place given to the notion of habit in moral philosophy and theology, as well as in the theory of knowledge. Yet this is exactly what St. Thomas does, and so we should take the time to follow his most pedagogically clear exposition of it.
We should therefore consider the opening articles of his so-called "treatise on habits" in the Summa theologiae. Before turning to his treatment of the general notion of habit (ST I-II, q. 49), let us take a moment to consider his general methodology throughout the Summa and, then, the specific placement of this treatise among the other topics discussed there.
Reading the Summa theologiae: Where the Treatise on Habits Stands
The Summa theologiae represents a very important development in the methodology of theology—within Latin Catholicism, but, more truly, in the history of the Church as a whole. As you know, the university theological training of St. Thomas's day relied upon the quasi-textbook of the twelfth-century bishop Peter Lombard, the Sentences. The structure of theological formation was to comment upon the topics gathered in these four books of patristic sententiae, engaging contemporary debates after providing a literal textual commentary. This, alongside public theological disputations and scriptural commentary, provided the backbone of university life. In a sense, it was also the inchoate format for the reform of clerical education—as we can see, for example, in how naturally St. Thomas transferred the methods of the university to the various studia where he taught between his Parisian appointments.
Noticing the pedagogical deficiencies in these methods, however, he set out to reform, quietly, the studies of the young friars in training. The fruit of this “pedagogical experiment” is the Summa theologiae. Much has been said about the structure of this work—and, as Fr. Cuddy will tell you, it is a topic deserving of its own treatment. I wish only to point out the implications of the scientific structure of the text, for this will prove revelatory for our own reading.
What is "science" in the Aristotelian register? The term does not refer to the same discourse we name by it today. The observable and the repeatable: this would seem to be science to our contemporary minds. But for the author of the Posterior Analytics—and for St. Thomas—it meant a different sort of discourse. Science, for St. Thomas, is a habit of mind that enables one to draw conclusions about a given subject, and about everything necessarily (per se) connected to that subject, ultimately resolvable to the first principles of that subject. When we look at the objective structure of such a discourse, we see a very regular pattern: the nature of something is delineated in its definition and its species; its per se properties, causes, and effects are considered; and then the other topics that are per se connected to this subject matter are taken up. Applied gradually over the whole course of the major topics connected with the primary subject of attribution, this yields a discourse whose explanatory structure has a kind of solidity, for it methodically unpacks the relations among truths. Through such knowledge we understand not merely an extensive body of truths; we come to understand the explanatory structure of truths—we see which truths explain other truths, step by step.
In the Summa theologiae, the great macro-structure is organized around God. This is not merely God the Creator, or the Good-God, or the One-God. We are speaking of the Triune God, of Him who is Father, Son, and Holy Spirit. The keystone of the Summa is the treatise De Deo (ST I, q. 2–43). From there the work gradually unfolds, showing the procession of all things from this God: the creative and conservative procession of all things (ST I, q. 44–119); the free agency of creatures made in the divine image (ST II); and the redemptive incarnation in Christ, applied today in His sacraments and brought to consummation in glory (ST III).
The discussion of habits falls within the immense work of the Secunda pars—more precisely, within the portion known as the Prima secundae, the first part of the second part. Here again we see the scientific methodology at work. Habit in general has a common character, an essence. This common essence has its own unique properties (as well as causes and effects), which will be found wherever the essence itself is encountered. Before discussing the specific sorts of habits—above all those which are the moral virtues—one should consider all of these matters, which will recur throughout the specific discussions. It is therefore a question of considering habit in general, in commune, before it is considered in speciale in the particular moral virtues discussed in ST II-II, the Secunda secundae.
We must, however, place this “treatise on habits” within the other subjects covered in this “common moral theology” the Prima secundae. Habits are discussed only after forty-eight other questions, with all their articles, have been dispatched. Opening these general moral principles, Thomas takes up the question of beatitude—the end—which is the central reference point for all his moral theology. As our Fr. Cuddy recently put it so well, in a paper given at a conference of moral theologians, Thomas's moral theology is not primarily a “virtue theory.” It is a “beatitude theory.” The moral theologian is constantly concerned to resolve his questions back to the first principle of moral action, namely the end. And this end is nothing other than the participated beatitude that fully flowers in the heavenly vision. This is the central axis of the whole Secunda pars.
But such beatitude is considered with a particular focus. It is not a question of the divine beatitude as it is in God Himself. That discussion has already taken place—at what is something like the "hinge" between God considered in what belongs to Him essentially (cf. ST I, q. 28) and the same God considered in the Triune distinction of Persons. The beatitude of ST I-II, q. 1–5 is this divine life, this divine beatitude, considered precisely as an act that marks the full perfection of the Christian life—the flowering of grace, the participated deity that is the life of the saints: definitively in heaven, in seed in our pilgrim state. It is the beatitude that we live as beings made in the image of God.
This beatitude is, we may say, “enacted” by us. In heaven it is the definitive act of the blessed; here below it is sketched out in many human acts, over the course of each of our particular histories as images of God. It is no surprise, then, that the topic following the “treatise on beatitude” is that of “human acts”: “Therefore, since beatitude must be reached through certain acts, it follows that we must consider human acts, so that we may know by which acts one arrives at beatitude, and by which the way to beatitude is impeded” (ST I-II, q. 6, proem). To this universal consideration of beatifying human acts—the central concern, really, of the whole Secunda pars—belongs the discussion both of the acts proper to the human person and of those which man shares with the animals. Thus the "treatise on human acts” includes a discussion of our intellectual and volitional acts of practical intelligence, considered both “psychologically” and “morally” (ST I-II, q. 6–21), as well as of the passions, which play so universal a role in our embodied human life (ST I-II, q. 22–48).
It is here that we reach the theologian's concern with habits. It is within this overall movement of the intellectus fidei—and especially within the context of the moral “beatitude theory” of which we have spoken—that we encounter St. Thomas's deployment of the philosophical tools of his age, tools that are perennial in their validity. Thus, as he opens his treatise on habits (ST I-II, q. 49–70), together with its shaded privation, vice and sin in general (ST I-II, q. 71–89), he remarks on the important transition this treatise marks in the rest of ST I-II. Having spoken of acts (and passions), he now turns to the principles of human acts. Such principles can be considered either as "intrinsic" to the agent himself or as "extrinsic." The extrinsic principles will be law and grace—not because law and grace are wholly external to the human agent, but because, before he can take up those topics, he must first consider the intrinsic, subjective principles of our action, namely our powers and habits. The powers, he notes, were already discussed in the Prima pars, where he treats the human person specifically from the perspective of creation (cf. ST I, q. 75–102, esp. 77–83). What must be discussed here, however, are habits, which play an important role as proximate principles of man's beatitude-bearing actions. This treatise on habits unfolds over a rich distribution of questions: some dedicated to the general notion of habit, its causes, its development (or regression), and its general ways of being distinguished; others to the (intellectual, moral, and theological) virtues in general, as the first great specific divisions of operative habits; and others still to the gifts of the Holy Spirit, the beatitudes, and the fruits of the Holy Spirit.
And so we come to the question at hand, with which he opens the discussion: what is the nature of habit? It seems a relatively simple question to those already acquainted with Thomas’s philosophy and theology. Yet we should take care to understand very precisely what St. Thomas proposes in these three articles, for all the rest of the treatise will be governed by a proper grasp of this essence, which is the raison d'être of every other topic discussed in it.
Article 1: Is Habit in the Genus of Quality?
To reach the essence of anything, we must attempt a definition; and this requires us to understand something of the genus and the difference that together express the specific essence under discussion. We are faced, then, with our first article: is habit in the genus of quality? Here a remark is in order regarding the ten “categories,” or “predicaments,” spoken of by the Aristotelians.
As you are aware, Aristotle divides being into ten categories, one of which is substance (which exists "in itself") while the rest are “accidents” (which exist “in another,” ultimately in substance). Among these accidents is numbered quality, which, quite generically understood, is “that which makes something to be such or such.” It is a rather broad definition, and we will see its various species shortly. For now it is enough to know that quality was envisioned as quite different from, say, quantity (by which something has parts outside of parts), or from action, or passion, and so on. Even so, this unique character is not, at first glance, completely clear. It can therefore be of use to us to follow St. Thomas as he attempts to place habit within this category.
There are three very clear objections to the proposition that habit is a species of quality: 1˚ Above all, “to have” seems to be very general. We can speak of something “having” a given quantity of matter, for example, or I can “have” a piece of paper in hand as I talk to a group of students. For that reason, “to have”—and hence habit—would seem to belong to more than one category. This is the so-called "post-predicamental" notion of habit, the sort of thing discussed as belonging to more than one category. 2˚ Moreover, especially in the Latin of Thomas's day, habitus was an intrinsically ambiguous term. It can mean something like “clothing”—as the English "habit" still refers to the distinctive clothing of professed religious. This kind of “having” was numbered as the tenth of the categories, “to-be-vested.” 3˚ Finally, as Aristotle himself says in the Categories, habit would seem to be a kind of disposition. But disposition involves a certain ordering of parts in relation to one another, which would seem to belong to another category, “position” or “posture,” indicating the way that quantified parts are related to one another in their particular place.
In the body of this first article, then, Thomas deals with the initial ambiguity present in the first two objections. The “having” spoken of here is not the general sense—the one that could be used, in loose and equivocal language, to refer to any sort of possession whatever. Taken in that way, yes, “having” would belong to all the categories or genera of being, and not to one specific genus. We must therefore recognize that when we ask whether habit is a quality, we do not mean it in this “trans-categorical” or “post-predicamental” sense, the sense in which it spreads across quality, quantity, relation, and the rest. Nor are we speaking of the external “habit”—the clothing of a religious, by which he is clad. In our inquiry we are concerned with something other than this tenth category.
So, to be clear, two meanings of “habit” have now been disambiguated and set aside: first, the “post-predicamental” sense of “having” that applies to many genera of being; and second, the specific sense of habitus that refers to vesture, to clothing in general. Rather, we may also understand habit as referring to how something is disposed or related (se habet) to itself or to something else. We could think of it as a kind of “mode of being disposed,” a modus se habendi (cf. Garrigou-Lagrange, De beatitudine, 416). It is not a question of being disposed in place—that is the disposing that belongs to “position” or “posture.” Rather, the “being disposed” in question concerns the way the capacities of a given substance are disposed (ad 3).
This very general-seeming remark in fact represents something centrally important for understanding habit among the various species of quality. And indeed the point emerges in the second article: is habit a distinct species of quality?
Article 2: Is Habit a Distinct Species of Quality
St. Thomas distinguishes the various species of quality, and we should attend to his own position, which he sets against the commentary of Simplicius (as can be seen in the text I have provided). This division of quality is very important, for it reveals something about the nature of habit itself as the preeminent species of this category. If we understand quality to be a certain kind of “mode”—that is, a measure or determination of substance—then such a measure can take place in a variety of ways.
In what ways can a substance be determined, or “measured,” in an accidental manner? St. Thomas answers: in relation to its nature; in regard to the action and passion that result from its natural principles (matter and form); or in regard to quantity. These are the principal ways in which something can be “measured,” or—to put it quite generally—"disposed," and from them arise the four species of quality.
The lowest and least important of these measurings takes place with regard to quantity. We can say that something is disposed in its figure or shape. In itself, this purely quantitative disposition of a substance is not subject to the language of good or evil (well or ill) disposition. It merely indicates the way the quantitative parts of a substance are arranged in relation to one another. This may have a bearing on the other kinds of quality a being can have; but of itself, quantity says nothing about ends and teleology, and so one cannot speak of good or bad ordering here.
If we now consider the action and passion that result from matter and form, we arrive at the third and second species of quality: sensible qualities (the third species) and powers (the second). For from the form of a given being there flow certain powers that qualify the substance in relation to operation—qualities such as memory, intellect, and will. Although such qualifications designate an ordering to action, they do not, of themselves, designate anything good or evil. Operation, as such, is not an end in itself; it is measured by something else, by the nature of the agent.
There remains, therefore, one final way of being qualitatively disposed or measured: in relation to the substantial nature itself. We can ask whether a being is well or ill disposed with regard to the perfection of its nature. This is the species to which habit belongs. Because a thing can be well or ill disposed in relation to its nature, we may say that this particular disposition is good or ill; for here we are speaking quite directly of the way a being is disposed—not in its quantity, nor in its capacity to undergo passion, nor in its capacity to act, but specifically and directly in relation to its nature, which is itself a kind of end, insofar as the nature is the principle of the thing's acts. Substances succeed or fail in being what they are to the degree that they exist and act in accord with their nature. To attend to this particular disposition—how well a thing is disposed in relation to its natural perfection—is to attend to the specific quality that is habit. It is the first species, because it is the most perfect and complete way that a substance can "hold itself" (se habet), namely precisely as regards the measure of its natural perfection.
We should note, however, that we are now faced with two senses of “disposition.” There is the sense in which quality itself is a kind of disposition—a disposition of substance, whether with regard to its quantity, or its action and passion, or specifically as regards its own substantial nature. This final and most perfect case is itself also a kind of "disposition," a disposition in relation to nature. But here we must draw a further distinction if we are really to understand what a habit is in its most specific nature.
Here St. Thomas's reply to the third objection is very important. He notes that whenever Aristotle says habits are qualities “difficult to change,” this is not a specific difference at the level of quality as such. It is, rather, a difference within the first species of quality. You see, we have been using the term "habit" somewhat loosely—and “disposition” loosely as well. Let us, for the moment, fix a single definition for the first species: a quality (that is, a disposition of substance) with regard to the very nature of that substance. This species can then be subdivided:
(A) a quality (=disposition of substance) with regard to the very nature of that substance that, by its very nature, is difficult to change
(B) a quality (=disposition of substance) with regard to the very nature of that substance that, by its very nature, is easily changed
It is to (A) that the term “habit,” in its strictest sense, is limited. Indeed, it is not uncommon to find scholastic authors writing in the Western European languages who reach for the Latin habitus to designate this sub-species (of the first species) of quality, precisely so as to jolt the reader into realizing that this preeminent “disposition,” or “habit,” is something quite unique and stable—the most perfect way a substance can be qualitatively disposed toward its natural perfection.
We should pause, however, to appreciate the qualification “by its very nature.” Let us begin with the examples Thomas gives. For (A) he names “sciences” and “virtues”; for (B), health and sickness. It is important to see that he is not merely contrasting spiritual-human habit-dispositions with merely bodily ones. An example drawn from other commentators on this passage makes the distinction clearer: science versus opinion (cf. Garrigou-Lagrange, De beatitudine, 417). “Science” is certain knowledge through per se causes, ultimately resolved to first causes. It is a habit of mind that is objectively secure: even when difficult to achieve, it nonetheless enables its bearer, on the basis of its objective principles, to possess certain and infallible knowledge. Opinion, by contrast, is not nothing. It is not ignorance, nor mere suspicion, nor some more or less doubtful knowledge. Opinion is an inclination of the mind which is nonetheless marked by a kind of uncertainty—a formido alterius, the fear that some other claim might be true. The man who opines is inclined, but not definitively, toward the position he holds. In other words, opinion is—in view of its intrinsic principles—unstable and relatively “easy to remove.” The mutability of its causes (common principles applied to a particular matter) is what makes it easily changed.1
Admittedly, we can sometimes hold strongly to our opinions, whether out of pride, fear, or sheer stubbornness. In such a case the disposition can take on a rooting that makes it subjectively difficult to remove—we all know the person who is simply “impossible” to reason with! Yet as regards its objective principles, opinion remains unstable. Similarly, imagine someone profoundly genial and agreeable by temperament. This general disposition might make him appear obedient in nearly every situation. And yet something unstable remains, for such a person may never quite be obedient on principle; so that, when some displeasing command finally comes, he shows that his “obedience” was only a disposition—something objectively easy to change.
We may also consider the person who possesses scientific knowledge (above mere opinion), or virtue (above mere dispositional action), and yet has not a fully settled character. The man of science may not truly understand logic: he demonstrates, indeed, but without a deep grasp of the rules of demonstration. This makes his science subjectively unstable, even though it rests on objectively certain principles. Or again, someone who has truly attained a virtue may retain various dispositional remnants of a long life of sin—as we all know well enough in our own souls. Such a person can objectively possess a habit, though the habit is in a subjectively weakened state. The later Thomists would say that this is (objectively) a habit which is (subjectively) in a state of disposition. Within one and the same species of science or virtue, one can pass from imperfection to perfection, as the human boy becomes a human man.
Thus, after this long investigation, we have the definition of habit in the strict sense: a quality, disposing a substance well or ill in relation to its nature, doing so by reason of a motive that is objectively difficult to change. In its parts:
Quality: We here have the remote genus, the formal reason of which is “that which makes a substance to be disposed in such or such a way.”
Disposing a substance well or ill in relation to its nature: This difference gets us the first and most preeminent way of being a quality (=disposition or quality in the broad sense).
Doing so by reason of a motive that is objectively difficult to change: This difference enables us to distinguish between habit and disposition in the strict sense.2
If we have spent this much time on the second article, it is because the essence of a subject is of critical importance. No property, no proper effect, no proper cause can be scientifically understood if we are inexact about the essence of a thing, as expressed in its definition.
Article 3: Is Habit Ordered to Act?
This leaves us, however, with a somewhat surprising situation: habit is not primarily defined in view of act. What is most essential is that habit is a mode of objectively disposing (a modus se habendi) a substance in relation to its nature, whether well or ill. But what about action? Do we not often say that virtues are "operative" habits, that they dispose us to act well? Are they not, then, most essentially ordered to acts? Do not habits merely help our powers in this ordering toward act?
In the third article, St. Thomas resolutely denies this. In the body of the article he opens by reiterating that what is essential to habit is that it disposes a substance in relation to its nature. Yet a nature is the per se principle of a being's motion and rest. It is the terminus of generation, the agentive principle of all a being's becoming. Nature, in other words, is oriented to operation and to the external productions that can follow from such operation.
Drawing here on Book Delta of the Metaphysics, he adds a further precision to the definition of habit. The first difference (disposing a substance well or ill in relation to its nature) can be expanded to read: “in relation to its nature—or in regard to something else, namely the end.” For this reason we can distinguish two different kinds of habit. Those which first determine the substance itself (for example, health), and only thereafter determine it in relation to an act (being actualized in a healthy way), will be called “entitative habits.” In the present example we are in fact speaking of an entitative disposition—health, which Thomas calls a “habitual disposition” in ad 3. In certain cases, however—habitual grace, for instance—there can be a strict habit that is entitative, stably determining the nature in question precisely as nature, while also calling for a further ordering of the soul's powers in relation to the perfection of that nature (indeed, of this “supernature”): namely, the further habits that are the various infused virtues.
When, however, a power is disposed toward good or ill action—“good or ill” always in relation to the nature in question (or the supernature, in the case of the graced person)—then we are speaking of what is called an "operative habit." But notice my carefully chosen words, which I will signal with emphasis: operative habits dispose the powers toward operation, yes—but primarily in relation to the nature in question. We say that justice orders the will in relation to the perfection of human nature, that courage orders the “irascible appetite” in relation to the perfection of nature, that science orders the intellect in relation to the natural perfection of stably knowing the truth, and so on. Thus, when we say that habits help to determine the powers (the second species of quality), this is not because habit is less perfect than power. It is because habit is something deeper: an ordering in relation to nature itself. Because nature precedes operation, habit is prior to power, as the most perfect case of quality (ad 3).
This brings us to the threshold of what I will take up in my next talk: why habits are necessary (a. 4)—so necessary, indeed, that we must take care not to lose the very formation of habits amid the cultural rise of AI technology. But I will leave that subject to its own forum.
For now, let us close by observing what we have accomplished. It may seem surprising, at first glance, that we have spent so much time on merely three articles of St. Thomas's Summa theologiae. And yet, in a sense, we have found ourselves at the junction point of the entire account of the virtues—at the point where we consider them in what is most generally essential to them all: their essence as habits. Thomas will have a great deal more to say about habits, and about the specific cases of virtue and vice that will fill not only ST I-II but the massive ST II-II. Yet in all these cases, virtue (a particular kind of operative habit) will cohere with this definition: a quality, disposing a substance well or ill in relation to its nature (or in relation to the end), doing so by reason of a motive that is objectively difficult to change.
A small error at the beginning can end by being a massive one. To be half a degree off matters little over a single inch; but over many miles it yields a large divergence from the destination we meant to reach. In our case, the destination is the truth about virtue. By understanding the essence of habit, we understand something very important about our nature: we must be put in right order. We stand in need of many qualifications, so that our nature might be rightly ordered both in itself and in its powers. And so we see, too, why it is that nature—or the “supernature” that is grace—is the foundational measure of our entire perfection. The work of a human life will be to act well: to be led by right reason, a right reason that deploys our powers in a way ultimately in accord with the right ordering of human nature and, above all, with the divine “supernature” given us through grace.
Because so little is said correctly nowadays regarding opinion and probable certainty, I welcome the reader to see the treatment presented in Gardeil’s treatment of this topic.↩︎
As a point of technical observation, this difference ultimately will only hold, strictly speaking, for those qualities that dispose a substance well in relation to its nature. In the case of a disposition that ill-disposes a substance, the relative stability is not equal to that which is found in the strictest case of habits. Thus, vices will not be habits in this most strict sense. For example, think of how the vicious person, lacking courage, fluctuates between cowardice in some scenarios and rashness in others. My thanks are owed to Nicholas Ramirez for reminding me of this important qualification.↩︎
