Thomas begins his discussion of virtue in the Prima Secundae by devoting q. 55 to its definition.Footnote ¹ Peter Lombard had drawn from Augustine of Hippo’s works the definition of virtue as a “good quality of the mind, by which we live rightly, which no one uses badly, which God alone works in a human.”Footnote ² In the first three articles of q. 55, Thomas argues that virtue is a good operative habit. In the fourth article he argues that Lombard’s Augustinian definition of virtue is the most complete definition. This definition became widespread because the work in which it appeared, Lombard’s Sentences, was the standard textbook for theology for many centuries. Thomas provides an account and defense of this standard definition not only in the Summa Theologiae but also in his early Commentary on the Sentences as well as in the roughly contemporaneous De Virtutibus in Communi, art. 1–2. However, in the Summa Theologiae Thomas more clearly connects this traditional definition with the more precise account of virtue as a good operative habit. His understanding of how the different definitions are related seems to be influenced by earlier writers such as Philip the Chancellor (d. 1236) and Albert the Great, who themselves inherited several definitions of virtue.Footnote ³ Thomas adds to this tradition in part by developing a lengthy and more sophisticated account of habits in general. Although his approach is heavily influenced by Aristotle’s Nicomachean Ethics, the order of the discussion and the details seem to be Thomas’s own.

Thomas’s argument for his definition of virtue makes assumptions that might be unfamiliar to some contemporary readers. Some definitions include the causes of what is defined or even different nonessential properties. Among the various types of definition recognized by Thomas and his contemporaries, the most important kind places the species that is to be defined in its most proximate genus. Each intermediate genus itself is a species of another genus, until we ultimately arrive at one of the ten categories, which is composed of substance and nine accidents. For instance, a human being would be defined as a “rational animal.” “Human being” is a species that can be defined by placing it in a genus and then indicating the difference that distinguishes it from other members of the genus. The species “human” itself has no species under it. It belongs to the genus “animal,” which is a genus that includes every living thing that has sensation. The difference “rational” distinguishes humans from other animals. The genus “animal” includes various species of animals and itself is a species of the genus of living things. Just as there is a lowest species that includes no other species below it, so there are highest genera, which are members of no other genera. Ultimately the highest genus of human beings is a substance, which is something that is a being on its own. The nine accidents, such as quantity and quality, have their being in a substance immediately or through other accidents that have their being in a substance.

We will see that virtues are habits, which are accidents that come under the genus of quality. Powers are accidents that are often jointed to organs that are substantial parts of the substances. For instance, the power of sight is joined to the eye and parts of the brain. Individual humans are complete substances. A virtue is distinguished from many other habits by being an operative habit. It inheres in powers that are rational or in some way subject to reason, such as the intellect, the will, and the sense appetites, which are powers whose acts are passions, or what we might describe as emotions. An operative habit in some way causes operations, which generally speaking are actions and more narrowly speaking are living activities that somehow remain in the agents, such as seeing, hearing, and the peculiarly human activities of thinking and willing. Operative habits are needed because of the indeterminacy of human reason, and they cannot be present in nonrational animals. Typical human operations are proving a mathematical theorem, returning a borrowed item, and stealing. A virtue is distinguished from a vice by being a good operative habit, because it is a source of good operations, which make the agent good.

A virtue perfects a human power in its production of a good operation. We will see that Thomas draws on many different traditional definitions in order to argue for and explain what virtue is. But the overall trajectory of this chapter is to show why Thomas thinks that virtue is a good operative habit and what it means to define virtue in this way.

Habits

Thomas’s understanding of habits is often neglected in accounts of his theory of virtues. Servais Pinckaers has argued that contemporary usage might mislead readers to think of habit as a kind of animal reflex or conditioning.Footnote ⁴ But according to Thomas, a habit is a particular kind of quality that other animals cannot possess, since habits inhere only in those powers that are either themselves rational or that participate in reason. Some habits inhere directly in the intellect and will, whereas others inhere in the sensitive appetites insofar as they are subject to reason. Habits are not what might now be described as a kind of physical habituation and conditioning, or “muscle memory.” Such conditioning resembles a habit but falls short of it insofar as it does not involve the will in any way.Footnote ⁵ Thomas calls such conditioning a “custom” (consuetudo).

Thomas and his predecessors were familiar with many definitions of virtue, which were taken both from Catholic writers and from ancient philosophers.Footnote ⁶ According to Albert and Philip, Lombard’s formulation is central even though it might seem to be incompatible with that of the philosophers. In particular, Philip and Albert state that the last part of this definition, which mentions God’s agency, does not apply to those virtues that are described by the philosopher but instead to those that are given by God.Footnote ⁷ Nevertheless, they both think that the preceding parts of the definition apply to all virtue, and they argue for the definition’s compatibility with Aristotelian definitions. Albert in particular connects the Augustinian definition to an Aristotelian moral and metaphysical understanding of virtue as a habit that inheres in the soul’s powers. For example, the definition describes virtue as a “good quality of the mind.” According to Albert, this definition rightly indicates that virtue belongs to the genus “quality,” since virtue is a habit.Footnote ⁸ Aristotelian habits are qualities. This quality belongs to the “mind” because it resides in either the rational part or those parts that obey reason.Footnote ⁹ Thomas seems to be influenced by Albert in his identification of the Aristotelian habit, which is a species of the category quality, with Lombard’s quality.

In the De Bono, Albert gives two definitions of virtue from the philosophers. First, he mentions Cicero’s definition of virtue as “a habit of the soul in the manner of a nature, in accordance with reason.”Footnote ¹⁰ Although Cicero was not an Aristotelian, this definition brings out the Aristotelian theme that virtue resembles another nature. Second, Albert mentions Aristotle’s definition of moral virtue in the Nicomachean Ethics, Book II, chapter 5, as “a voluntary habit consisting in a mean relative to us, determined by reason, and as the wise human will determine it.”Footnote ¹¹ Although Philip and Albert in their earlier years did not have access to the whole of the Nicomachean Ethics, they did have Latin translations of the first three books, which include Aristotle’s definition of virtue. Both Philip and Albert adopt this definition of moral virtue and attempt to show how it is compatible with Lombard’s definition and various texts from Augustine and other Catholic authorities.

The identification of the scholastic and Augustinian “quality” with Aristotle’s “voluntary habit” might seem forced. For instance, Aristotle did not have the same explicit and well-developed notion of the will that was possessed by medieval philosophers.Footnote ¹² Consequently, the notion of voluntariness for Christians was at least verbally connected with a power of the soul that Aristotle did not mention. This verbal connection does not exist in Greek. For instance, medieval translations use the word “voluntas” to translate Aristotle’s “simple wish” (boulesis), but Thomas and others recognized that this meaning of “voluntas” was distinct from its use as signifying the will.Footnote ¹³ Moreover, the related Latin term that can be translated as “voluntarily” or “willingly” (voluntarie) was used for action that has its source in the agent, and more narrowly an action that comes from the agent’s intellect and will. Consequently, it was natural, if perhaps anachronistic, to identify Aristotle’s notion of a voluntary action in its fullest sense with their own understanding of an action that has its source in the intellect and the will.

According to Aristotle, nonrational animals and children are capable of action that is voluntary in a wide sense even if it is not rational.Footnote ¹⁴ He contrasts voluntary action in a wide sense with that voluntary action which is the proper act of virtue, namely choice (prohairesis/electio). Aristotle mentions the act of choice but not the will as a faculty. In contrast, Philip’s understanding of the importance of the will as a faculty can be seen in his defense of the Aristotle’s statement that “Virtue is a habit by which someone is good and renders a work well.”Footnote ¹⁵ Philip mentions as an objection that Aristotle’s statement is too broad because it applies to both nonrational animals and children, who themselves are not able to use reason. Philip states that the last part of the definition, “[which] renders the work well,” applies only to action that involves the will and intellect and not to the actions of those who lack reason.

In the Summa Theologiae, I-II, q. 55, art. 4, Thomas follows Albert and Philip on many of these points, especially in their way of reconciling Aristotle’s account of virtue with Lombard’s Augustinian definition. Nevertheless, before he discusses the Augustinian definition he devotes several questions to habits in general and several articles to the definition of virtue. In q. 55, art. 1–3, Thomas describes virtue as a good operative habit. This definition seems to be essential in that it gives the genus (operative habit) and a specific difference (good). However, we will see in Chapters 2 to 4 that not all virtues are good in the same way. For Thomas, as for his predecessors, the word “habit” is a technical term that subsumes virtue under the Aristotelians quality of “habit,” which helps the agent to act freely and with knowledge. In the immediately preceding qq. 49–54, Thomas discusses the nature of habits, the human powers in which they reside, how they are caused, and the way in which they are distinguished from each other. Thomas’s lengthy discussion of habits surpasses previous accounts and illustrates his use of not only the Nicomachean Ethics but the Aristotelian corpus as a whole. He uses Aristotle’s definition of a habit to explain why habits can be present only in rational powers and those powers that are subject to the rational ones.

Thomas uses different arguments to support the thesis that virtue is a habit. Sometimes he more or less follows Aristotle’s arguments that virtue cannot be a passion. In other texts he develops further arguments, according to which virtue cannot be an act. For the most part, these arguments show not so much that virtue can be a habit but that it cannot be something other than a habit.

In the Commentary on the Sentences, Thomas states that virtue allows an act to be proportionate to its rational power not only according to its substance but also according to its mode.Footnote ¹⁶ Rational powers can without habits produce the kinds of acts that can be virtuous, but they will be done without pleasure and with difficulty, since such acts will not be connatural to the agent. A natural power does not need a habit, since a complete nature on its own is directed to a perfect act. God’s power is capable of different acts and yet it is proportionate to any perfect act. Consequently, neither natural powers nor God needs habits to act well. In contrast, human powers on their own are not adapted and assimilated to virtuous acts. Habits are necessary because human powers are both undetermined and imperfect. Only a person who has the virtue of chastity chooses chaste acts in a way similar to that in which a heavy object falls downward.

In the Summa Theologiae, Thomas begins his argument for the conclusion that virtue is a habit by stating the premise that a virtue is a perfection of a power.Footnote ¹⁷ Since acts are perfections of powers, it follows that a perfection of a power is that which makes powers act. Habits are such a perfection. As in the Commentary on the Sentences, Thomas notes that powers need habits only if they lack determination on their own. In the Summa Theologiae he remarks that these undetermined powers are the rational powers that are proper to humans and not to animals or other intellectual creatures. Having argued in the previous questions that human powers are perfected and determined by habits, he easily concludes that human virtues must be habits.

Thomas brings together a variety of Aristotelian texts in the De Virtutibus in Communi, art. 1. In the body of this question he cites three statements from Aristotle, namely the statement in the Latin of the De Caelo that virtue is “the peak of a power” (ultimum potentiae), Aristotle’s remark in the Nicomachean Ethics that virtue renders well the agent and the work, and his statement in the Physics that it is a disposition of the perfect for the best.Footnote ¹⁸ Thomas connects these statements with each other by noting that a perfection of the power makes not only the act good but also the end, which is the agent’s perfection. These three statements apply both to all human virtues and to virtue more broadly considered, such as the virtue of a horse or of a stone. In this text he considers human virtue as a kind of virtue taken in a wider sense. We can clearly see here the connection between the notion of virtue itself and that of an excellence or perfection.

Thomas’s argument that human virtue is a habit is based on a description of the various kinds of powers. According to Thomas, powers can be divided into those that are only acting, those that are acted upon and acting, and those that are merely acting upon.Footnote ¹⁹ Instances of the first kind of power include God’s power, the agent intellect, and merely natural powers. These powers do not need virtues because they are themselves complete. The virtues are the powers themselves. The third kind of powers, namely those that are merely acted upon, do not need habits either in order to act. The exterior senses belong to this group. For example, the eye perceives color when the eyes when it is opened and functioning properly. The power simply needs its object and the medium by which it sees. Powers that belong to this third group can themselves be called “virtues,” in a different but related meaning of the term. The eye sees by the power of sight, which is its “virtue.”

Virtuous habits are needed only for those powers of the second kind, that both act and are acted upon.Footnote ²⁰ Insofar as they need habits, these powers lack determination to act. Thomas defends the same thesis that Aristotle argues for in the Nicomachean Ethics, Book II, chapter 5, in which Aristotle distinguishes virtues from passions and powers. But Thomas gives another argument for the distinction. He remarks that, since virtues are needed by the powers, they cannot be the powers themselves. Virtues are not passions because passions are acted upon, whereas virtues are a form that inheres in a power and helps it to act. Since they inhere in the power and do not belong to the other species of quality, they must be habits. Thomas states that virtue is needed in such powers in order for the operations to be uniform, prompt, and pleasurable. Since the powers are undetermined, they need habits in order to be inclined to one act rather than another. Since the agents are not inclined to the acts by the powers themselves, the agents will take longer to act, since they need to think more explicitly and at greater length about what they are going to do. Furthermore, habit makes a kind of act almost natural. Since an object is pleasurable because it is somehow suitable or fitting to a power, habits make their acts pleasurable for the agents. Thomas quotes Aristotle’s Nicomachean Ethics in support of the position that virtue makes acts prompt and pleasurable.Footnote ²¹

In all three texts, namely the Commentary on the Sentences, the Summa Theologiae, and the De Virtutibus in Communi, Thomas is primarily, if not only, concerned in his choice of objections with arguing that virtue is a habit and not an act or a power. He does not use the Aristotelian arguments for the position that it is a habit rather than a power or a passion. One reason might be that the argument in these texts is meant to establish that every virtue is a habit. Aristotle gives the argument in the part of his work that concerns moral virtue. Thomas gives the argument in contexts that include discussions of other kinds of virtue.

Whereas Aristotle argues in the Nicomachean Ethics that virtue is a habit by showing that it cannot be a passion or a power, Thomas also argues that it is not an act. This aspect of his discussion might reflect a Christian cultural context according to which virtue is identified with love and regarded as meritorious. Love is an act that can inform many acts, and merit accrues to acts rather than habits. Consequently, a person might be inclined to conclude that virtue is an act and not a habit. However, Thomas incorporates Augustine’s description of virtue as love into his Aristotelian account of how virtues are habits. For instance, in Prima Secundae, q. 55, art. 1, the second and fourth objections appeal to definitions from Augustine in order to argue that virtue is an act or perhaps a relation. The second objection cites Augustine’s claim that “virtue is the good use of free choice (liberum arbitrium).”Footnote ²² If virtue is a use, then it is an act and not a habit. Thomas replies by stating that this use is only the act of virtue. Augustine’s statement is not about virtue itself but about its proper act. The fourth objection recalls Augustine’s statements that “virtue is the order of love” and that “the ordering which is called virtue is to enjoy that which should be enjoyed, and to use that which should be used.”Footnote ²³ According to Augustine, use (uti) and enjoyment (frui) are kinds of love. We love a good through use when we love it for something else. We enjoy something when we love it for its own sake. Use is ultimately for the sake of enjoyment. In these passages Augustine seems to be saying that virtue is an act or relation of love and not a habit. Thomas replies to this interpretation by stating that virtue is the habit that orders this love. In objection three, it is argued that virtue is an act because it is meritorious. Thomas replies that virtue is meritorious insofar as it is a principle of acts and not an act itself.Footnote ²⁴ He responds to each of these three objections not by rejecting the contents of Augustine’s texts but by showing that when understood correctly they do not conflict with the Aristotelian account.

Subjects of Habits

Thomas holds the view that habits inhere in a power or a nature. Thomas’s discussion of habits therefore presupposes the account of the human soul and its powers that he presents in the Prima Pars of the Summa Theologiae.Footnote ²⁵ His whole ethical theory and his moral psychology in the Secunda Pars to some extent depend on this earlier discussion. Thomas’s description of powers can be confusing, since there is a verbal connection in Latin between powers and potencies.Footnote ²⁶ In Thomas’s Latin, the word “potentia” can be translated in a general way as “potency” and more particularly as “power.” Consequently, in order to understand how habits are related to powers, it is helpful in English to distinguish between a “power,” which narrowly refers to the soul’s capacities to act, and a “potency,” which can be contrasted with act in a variety of ways. The wider act/potency distinction is fundamental to the physics and metaphysics of both Thomas and Aristotle, and as such is incapable of definition.Footnote ²⁷

The different kinds of change involve different kinds of potency. We can describe prime matter as in potency to first act, which is the act by which a substantial form determines it to a particular kind. Similarly, the substance itself, although already in first act, can be in potency to further act, as when we say that a substance such as a boy is potentially tall. The substantial form of living beings is the soul. It makes a particular body and its matter exist as a kind of thing that lives and, perhaps, senses and understands. It actualizes the matter so that the composite is a member of a living species. Only certain kinds of things can be changed substantially into a human being, such as eggs, water, and even bacon. Similarly, different substances are often in potency to different accidents. Only humans are in potency to becoming musical or mathematical. Gerbils lack such potencies.

More narrowly, potency covers not only a potency to being actualized by a form but it can also apply to a kind of ability, namely one whose actualization is an act or operation.Footnote ²⁸ Such a potency or power of the soul is a principle that is capable of a certain kind of act. For instance, dolphins and gerbils can digest and reproduce, but they do not always do so. The substantial form cannot by itself be the immediate principle of digestion or reproduction, since it is always present and accounts for why the dolphin is a dolphin and a gerbil is a gerbil. Since the soul is a principle of first actuality, such acts require a potency that is intermediate between the soul and the act or operation. It is in this way that the Latin word (potentia) that is translated as “potency” is often also translated as “power” or “capacity.” A power or capacity is the kind of potency that is a principle of operations. The soul makes the animal a kind of living substance, and a power makes it possible for an animal to perform a particular kind of act. Gerbils and dolphins are able to reproduce and eat because both gerbils and dolphins have the vital powers of nutrition and reproduction.

In the De Virtutibus in Communi and to some extent the Commentary on the Sentences, Thomas clarifies the way in which habits such as virtues belong to powers.Footnote ²⁹ He notes that accidents do not subsist and consequently their existence must be supported by a subject. Consequently, in a sense the soul or the soul-body composite is ultimately the subject of all accidents, including habits. Nevertheless, some accidents can belong to others insofar as they are related to them as potency to act and as effect to cause. These accidents belong to the substance by means of other accidents. For example, a color belongs to a substance by virtue of another accident, namely the color’s surface, which belongs to the genus of quantity. The color actualizes the surface, even though ultimately both the color and the surface are supported by the substance composed of form and matter. Similarly, a habit is ultimately supported by the soul or soul-body composite by means of the power that it actualizes.

Habits do not belong immediately to the soul or the composite but rather to an accident that inheres in the soul. Whereas the soul belongs to the genus “substance” insofar as it is the formal principle of the substance, power belongs to the genus “quality,” which is the genus of accidents that modifies substance in itself.Footnote ³⁰ This genus “quality” has four species directly under it, namely power, habit or disposition, sensible quality, and figure or shape. For Thomas, an agent acts by means of her powers. The agent might be most properly the whole organism or less properly an organ or other subject.Footnote ³¹ For instance, we might say that a human sees with her eye but also that her eye sees. We might only very loosely say that her power of sight sees. Powers are principles that are intermediate between a living substance’s essence and its operation. Properly speaking, operations and powers other than intellectual ones belong to the conjunct and not to the soul, and the subject of the powers is also in a way the subject of the operations. The conjunct, such as the human, has parts that can be subjects of operations and powers, such as the hand, the foot, and the eye. The nonintellectual powers inhere in the conjunct. The intellectual powers inhere directly in the soul. In this way we can say that a human understands with her soul in the way that she sees with her eye. Strictly speaking, a power that is in a bodily organ cannot be a subject because it is the wrong kind of part.

Powers are distinguished from each other by formal objects, or what they are about.Footnote ³² For instance, sight has color as its formal object, whereas hearing’s formal object is sound. We might hear and see the same object, such as a rubber ball or an automobile, but the formal object is specific to a sense. For instance, I can see a yellow car and a blue automobile because redness and blueness are both species of color. Passive powers, such as seeing and hearing, have formal objects that are principles of their activity. Active powers, such as reproduction and moving in place, have formal objects that are goals to which they are directed. According to Thomas, there are five genera of vital powers: vegetative, sensitive, intellective, appetitive, and locomotive.Footnote ³³ The vegetative powers are common to plants, nonrational animals, and human beings. These powers have as their subject the body to which the soul is united. For instance, nutrition and growth conserve and extend the living body, and reproduction produces another living body of the same kind and even with some of the same matter.Footnote ³⁴ Such vegetative powers are not perfected by habits.

Some powers are common to both nonrational animals and humans, whereas others are present in humans alone.Footnote ³⁵ It is worth considering the different species of human powers in order to understand why some can receive habits and others cannot. Some powers receive similitudes of external objects, whereas other powers incline the animal towards other objects. Cognitive powers, including the senses and the intellect, receive similitudes of external objects. The outer senses directly receive the sensible species, and the inner senses coordinate, store, and add aspects of suitability and time to them. Sensation is concerned with the accidental qualities of the material individual. There are about five external sense powers and four internal sense powers.Footnote ³⁶ In contrast to sensation, which is about singulars, the human intellect is most apt to know adequately the natures of material substances.Footnote ³⁷

The intellect consists of two distinct powers, namely the agent intellect, which makes the individual material objects actually intelligible, and the possible intellect, which apprehends, judges, and reasons.Footnote ³⁸ The possible intellect changes the functioning of two interior senses.Footnote ³⁹ In animals the estimative sense judges by instinct the suitability or dangerousness of perceived objects, and the memory allows some sense of the past. For example, a sheep judges by instinct that wolves are dangerous and retains some notion of past experience with a wolf. In humans, two of the four internal senses are specifically distinct because of the way in which they depend on the intellect. The estimative sense is instead the cogitative sense, or particular reason, and the memory is reminiscence, which involves an intellectual grasp of time. The cogitative power is particularly important in human action and emotion, since it judges concerning particular actions and experiences.Footnote ⁴⁰

Two powers incline the living substance towards something else, namely the power of appetite and movement in place.Footnote ⁴¹ The appetitive powers are particularly important for Thomas’s moral psychology. There are three appetitive powers. Two appetitive powers belong to the sense appetite, namely the concupiscible appetite and the irascible appetite.Footnote ⁴² As sense appetites, these powers are common to other animals, and they incline their possessors towards a sensibly perceived good or away from a sensibly perceived danger. The acts of the sense appetites can be described as “passions” or “emotions.” The concupiscible appetite involves the sensible good in itself, whereas the irascible appetite involves this good under the aspect of difficulty. For instance, a dog through her concupiscible appetite might desire to eat a steak because she loves it. She is sad when the human eats the steak. Through the irascible appetite she might hope that she can have leftovers even while she is afraid that the steak might be completely eaten. The concupiscible appetite is capable of such passions as love, hate, desire, aversion, hope and sorrow. The irascible appetite is capable of passions such as hope, despair, daring, fear, and anger. In animals these appetites are directed by the estimative power, whereas in humans they are directed by the cogitative.

The rational appetite or will is capable of such passions but only in an extended way.Footnote ⁴³ The will follows the good that is apprehended by the intellect.Footnote ⁴⁴ Consequently, its object is the good in general rather than any one particular good, and it can freely choose between some particular goods. Unlike some of his predecessors and contemporaries, Thomas denies that there is a distinction of powers in the will between the concupiscible and the irascible.Footnote ⁴⁵ His reasoning is that since the will, unlike the sense appetites, is concerned with the good that is generally perceived, its object cannot be divided in such a way that would entail a division of powers. Since humans are the only animals that have reason, they are the only animals that have a rational appetite or will. We will see that only some of these human powers are capable of being subjects of habits, namely those that are rational or those that participate in reason. The intellect and the will are essentially rational.

When Thomas describes virtue as a perfection of a power, he interprets “power” in this context as referring to powers for acting and to a potentiality for being. In this way “power” includes both matter and the powers of the soul.Footnote ⁴⁶ Consequently, “virtue” includes both the form that actualizes matter and the habits that inhere in powers. An important premise of Thomas’s argument is that human virtue is concerned with that which is proper to humans and not to other animals or bodies. Reason is the property that sets humans apart. Consequently, Aristotle and Thomas argue that human perfection involves rational activity. Although virtue in its wide sense might describe any sort of actualization of a potential, the human virtue under discussion is concerned with rational activity. Consequently, human virtue is neither a disposition of the body nor of some power that is common to the body and the soul but a habit that inheres either in rational powers or other powers insofar as they are rational by participation. It is a power for acting. Since this habit is concerned with the activity of these powers, it follows that human virtue must be an operative habit. It is directly concerned with human operations.

Not all powers can be subjects of habits. According to Aristotle and Thomas, operative habits allow us to think, act, and feel better or worse than we would otherwise be able to. The habits that produce operations belong to those powers that are rational or in some way obedient to reason.Footnote ⁴⁷ They are not unthinking bodily reflexes. Nonrational animals lack such habits because their powers function according to instinct. They might develop something like operative habits insofar as they have been trained to act in a particular way by human reason. But true habitual action is not instinctive but rather a result of a power that has been perfected by a habit. The sense powers and appetites are capable of being perfected by habits only to the extent that they are obedient to reason, as when someone habitually feels a passion such as anger or the desire for food.

Some habits can inhere in the possible intellect and in the will even if in some way they require bodily dispositions. Thomas states that the interior senses can be subject to habits only to the extent that they dispose the possible intellect to act. Such habits are principally in the intellect and only secondarily in the inner senses, such as the memory.Footnote ⁴⁸ In another context, Thomas writes, “just as the act of the intellect is indeed principally and formally in the intellect itself, but materially and dispositively in the inferior powers, the same should be said of a habit.”Footnote ⁴⁹ In this life our intellectual activity uses sense information. Since this sense information is in the inner senses, the inner senses and most properly their organs are in a way subjects of intellectual habits.

Thomas’s understanding of the virtues depends on his interpretation of the Aristotelian thesis that the sense appetites can have habits because they are in a wide sense obedient to reason.Footnote ⁵⁰ Using Aristotelian terminology, he describes this obedience as political and royal, as opposed to despotic.Footnote ⁵¹ The reason why this obedience is political and royal, is that the sensitive appetites are directed by the cogitative power, which itself participates in reason and obeys reasoning concerning universals. We can, for instance, influence our fear of flying by considering its relative safety in comparison with automobile travel. These passions do not obey reason in the way that our bodily members do. I can lift up my hand whenever I want, but I can quell fear or cause sensitive love at will sometimes only indirectly. Thomas thinks that many of these powers can be subjects of habits. Nevertheless, he thinks that only subjects with intellects and wills can have such habits, even though such sensitive powers are also possessed by nonrational animals. Moreover, he thinks that even some of these shared powers sometimes possess habits in a secondary way.

Some powers are capable of being modified by habits or dispositions, which are another species of quality.Footnote ⁵² According to Thomas, “A habit means a certain disposition with respect to the order to the nature of the thing, and to its own operation or its end, according to which the things is well or badly disposed to this.”Footnote ⁵³ Why do the powers need to be modified in some way in order to operate well or poorly? We can see and digest with the powers that we have at birth. Only some powers need to be disposed by habits. The reason is that many powers can be determined in different ways. For instance, we might develop the ability to do geometry or arithmetic, or we might consistently make certain mistakes. Similarly, we can learn how to paint or make music well or poorly. There can be a bodily component to these skills, but the bodily component itself results from the original decisions made by the will and directed by the intellect. When a potency is capable of being determined in different ways, then there is a need for a habit to make sure that the act can be performed consistently, without much thought, and pleasurably. Someone with the habit of geometry does not need to struggle when setting forth simple proofs. Similarly, it would be frustrating for a painter to relearn each day the basic principles of painting.

A habit not only produces a particular kind of act, it also causes the kind of act to be done in a particular way, namely pleasurably, readily, and easily.Footnote ⁵⁴ Thomas often states that vice or virtue is natural in the sense that “custom is another nature.”Footnote ⁵⁵ These features of the act result from the fact that they are connatural to the habit that causes them. A habitual act’s connaturality indicates an essential feature of habits, at least if the word “habit” is taken in the strictest sense. According to Thomas, there is a connection between the description of habit as another nature and Aristotle’s description of a habit as a stable quality. Thomas writes:

The effects are connatural to the way in which the agent has been modified by the habit. Someone who habitually understands geometry is the kind of person who is able to construct geometrical proofs as if the activity were natural to him.

Thomas discusses habits along with dispositions, which can be either specifically distinct from habits or imperfect versions of them.Footnote ⁵⁷ We will see that the virtues can be dispositions that are imperfect habits and that such dispositions can exist in those creatures that possess reason. In contrast, the other kind of dispositions, which are specifically distinct from habits, are common to nonrational creatures. Arabic, Latin, and Greek writers had generally understood all dispositions as members of the first species, namely as imperfect habits. Latin writers are in particular influenced by Boethius’s presentation of this position in his commentary on Aristotle’s Categories.Footnote ⁵⁸ According to this explanation, disposition differs from habit even less than Socrates’s humanity differs from Plato’s humanity. Socrates and Plato are specifically the same, but they differ as persons. A disposition differs from a habit only in the way in which an older Socrates differs from Socrates as a child. A disposition itself becomes a habit when it becomes more permanent.Footnote ⁵⁹ Disposition is distinct from habit because a disposition is unstable whereas a habit is lost only with difficulty. On this account, the formal characteristic of the disposition and habit is the same. The difference between them seems to be that the agent possesses a disposition imperfectly and a habit perfectly.

Thomas’s most significant passage on habits in relation to dispositions is the Summa Theologiae, I-II, q. 49, art. 2, ad 3. In this passage, he makes a threefold distinction between 1) disposition as a genus of habit, 2) disposition as an imperfect habit, and 3) disposition as a distinct kind of quality from habit. The second and third kinds of disposition are both easily changed (facile mobilis). Thomas first distinguishes between that disposition which is a genus of habit and included in the definition of a habit and those dispositions which are distinct from habit. In this first sense a habit is a kind of disposition. The second and third kinds of disposition are distinct from habits. In these second and third senses of the term “disposition,” a disposition is easy to lose whereas a habit is stable. These easily lost dispositions are divisible into the second sense of “disposition,” which shares a common name with habits, and the third sense, which indicates dispositions that are distinct in kind from habits. The second sense is the same in kind as a habit but imperfect. It corresponds to the traditional usage, which Thomas usually follows in his other writings and later in the Prima Secundae.Footnote ⁶⁰ In this sense justice or temperance might be a disposition and not a habit if it is imperfect. However, the passage under discussion explicitly distinguishes between dispositions that are unstable on account of their possession by the agent and dispositions that are unstable on account of their species. This latter kind of disposition, which is the third, includes sickness and health, which can easily be lost on account of their formal characteristics. This third kind of disposition is not operative, since it is concerned with the nature rather than with operations. It changes when the relevant qualities change. Such specifically distinct dispositions are always unstable on account of their objects even though they might be firmly possessed by some subjects. Such dispositions are essentially unstable, whereas the other kinds are only accidentally unstable.

When discussing the way in which dispositions differ from habits on account of their instability, it is important to consider the source of the instability. Health and beauty are unstable because they are corporal dispositions.Footnote ⁶¹ They have changeable bodies as their subjects and therefore are themselves easily changed. They always remain the kinds of things that are unstable. In contrast, a virtue or science is stable because it is a quality of the soul. The difference between a disposition and stable habit in this context involves the way in which it is perfectly or imperfectly possessed in the subject. The subject itself, namely the power in which the habit inheres, presents no obstacle to the quality’s stability. When perfectly acquired, the intellectual virtues acquired through acts of knowing and the moral virtues are difficult to lose. Moral virtues are more difficult to develop than demonstrative sciences are, since their possession requires many more acts.Footnote ⁶²

This instability of bodily dispositions helps to explain why bodies cannot be the subjects of habits that are essentially stable.Footnote ⁶³ Merely bodily operations result from the nature of the body and do not need habits to perfect them. In living substance, the soul is the principle of even those vital operations that are carried out by means of the body. But the operations belong more to the soul insofar as they are less determined to occur in only one way. Consequently, habitual dispositions such as beauty and health primarily involve bodily options and consequently inhere in the body. But habits more narrowly speaking are essentially stable dispositions that are ordered to operations of the soul. Consequently, essentially stable habits such as virtues and sciences must exist in the soul, at least in a primary way. It is only in a secondary sense that habits can be said to be in the bodies insofar as the bodily composition of the animal helps the soul to act more quickly and easily. Moreover, even though such bodily dispositions might be stable on account of their individual subjects, they remain subject to change in a way that qualities of the soul are not.

The distinction between habits and specifically distinct dispositions indicates why moral virtues and sciences must belong to the soul’s powers.Footnote ⁶⁴ Broadly speaking, a habit or disposition can be in the soul in two ways. First, it can be present in the soul as a disposition to something higher. Thomas explains health and habitual grace in this way. Just as health is a disposition of the body as ordered to the soul, so habitual grace is a disposition of the soul in order to the divine nature. In this same way a habit or disposition can also be an inordinate disposition and lack of harmony. Thomas explains illness and original sin in this way.Footnote ⁶⁵ Second, a habit can be present in a power. Such habits, since they involve operation, perfect those powers that are principles of operation. The operations are made better or worse by them.

Operative Habits

In I-II, q. 55, art. 2, Thomas argues that virtue is an operative habit. Although later writers would distinguish between operative and entitative habits, Thomas himself does not use the word “entitative.” Nevertheless, he explicitly distinguishes between operative habits and habits that are not. The importance of this distinction between kinds of habits can be seen in light of its denial by later authors. For instance, Peter Aureol (d. 1322) and Durandus of Saint-Pourçain (d. 1334) hold that the powers and not the habits are causes of a human act.Footnote ⁶⁶ According to their view, no habits would be essentially operative. In contrast, Francisco Suarez (1548–1617) argues that all habits are essentially operative.Footnote ⁶⁷ Thomists in response to both groups defend the distinction between operative habits and nonoperative or entitative habits.Footnote ⁶⁸

The position that all habits are essentially operative might seem to be similar to Thomas’s position that all habits in some way involve an order to operation, which he defends in I-II, q. 49, art. 3. But Thomas distinguishes between two relevant kinds of order. The differences between the kinds of order reflect the definition of habit as a disposition with respect to a nature or with respect to an act or end. A habitual disposition such as health is in order to a nature. Consequently, it is directed to an act only insofar as nature is a principle of action. In contrast, an operative habit is directly concerned with the operation or end. Consequently, it can be denominated as “operative” in contrast with the kind of habit that is concerned with operation only by means of a nature. Thomas’s distinction between habits that are operative and those that are not consequently depends on Aristotle’s definition of “habit,” which includes both nature and operation.

The main point is that such operative habits exist in order to modify actions. These actions need such modification because they are in some way undetermined. Animal actions, even though they might be similar to human actions, are ultimately explained by instinct. Human actions have their source in the intellect and in the will, which are to some extent indeterminate. Consequently, such properly human actions need to be perfected by habits. Properly speaking, habits can exist only in the possible intellect, the will, or the sense appetites. The possible intellect and the will can be determined to action by habits. Since human sense appetites are to some extent subject to reason, they can also be properly subject to habits. In contrast, the internal senses themselves are not principally subjects of habits, although, in a way, they can be modified to cooperate with the intellect.

The sensitive appetites can be the principal subjects of virtue, but the sense powers, including the inner senses, cannot.Footnote ⁶⁹ The reason for this difference rests in the way that a good work is made complete. The perfection of human action often finishes with that of the sense appetite, but the perfection of knowledge starts with the senses and ends in the intellect. The activity of the will, which is the rational appetite, extends to that of the sense appetite when the will moves the sense appetite. The completion of virtue can be in the sense appetite. But the direction of influence is the other way for cognition. The works of the inner senses are ordered to intellectual knowledge. In this way the inner senses move the intellect. The completion of knowledge is not brought about in the inner senses.

Thomas’s understanding of the connection between habits and rationality is perhaps at odds with some later notions, according to which a habit is a kind of physical or mental conditioning that makes an act unthinking. According to such a view, habits could even be obstacles to human freedom. For Thomas, operative habits perfect the action of the intellect and the will either by directly inhering in these powers or by inhering in powers that participate somehow in their activity. A conditioned psychological response would not be habitual in this sense. A habit might cause such conditioning, but the conditioning would be distinct. Operative habits belong only to creatures that have an intellect and a will.

A Good Operative Habit

Both Thomas and Aristotle think that the ultimate end of humans is in one sense happiness and in another sense God, or the First Mover. They state that happiness consists in operations that are proper to humans. Happiness is consequently the ultimate end of human beings, and the ultimate end is the first principle of human action and ethics. They also hold that there is one final end of the universe, which Aristotle describes as the First Mover.Footnote ⁷⁰ Thomas follows a long philosophical and theological tradition in identifying this First Mover with God.Footnote ⁷¹ He explains that God is the ultimate end of the entire universe and all human beings insofar as he is a thing that is to be attained, much in the same way that money is the final end of the miser.Footnote ⁷² But when we consider the human attainment of this end, the ultimate end is the good for the soul that is happiness. Virtue is part of the definition of this good of the soul.

Before looking at their description of the human good, it is worthwhile to consider the term “happiness,” which is usually used to translate the Greek eudaimonia and the Latin beatitude. Other words are sometimes used, such as “flourishing” or “beatitude,” but there seems to be no fully satisfactory translation in modern languages. Alasdair MacIntyre states that happiness is now generally understood as “a state of only positive feelings.”Footnote ⁷³ He notes that from the standpoint of a Thomistic Aristotelian, there might be good reasons to be unhappy in this sense.Footnote ⁷⁴ For instance, one might have good feelings in a bad situation because of one’s low expectations. Moreover, one might irrationally feel great in the face of terrible moral or physical evils. In contrast, for Aristotle and Thomas, happiness consists in leading what we might describe as a worthwhile life. It involves activities that are desirable for their own sake, although they may be desirable. Positive feelings have many internal and external causes, but the human end is there for us to discover and achieve. Consequently, there is a deep incompatibility between the happiness that is discussed by philosophers such as Aristotle and Thomas and the concept of happiness that is used by contemporary economists, political scientists, and indeed many ordinary persons. For lack of a better alternative, we will retain the term “happiness” for the attainment of the human end that is described by Aristotle and Thomas.

Aristotle and Thomas state that happiness is an operation in accordance with reason.Footnote ⁷⁵ Aristotle writes, “the human good will be an operation according to virtue, but if there are many virtues, according to the most perfect and best.”Footnote ⁷⁶ A substance’s perfection is connected with its proper function, which is based on the kind of substance that it is. For instance, dolphins, trees, and minerals all have different natures and consequently different proper functions. Minerals tend to stay what they are unless they are acted upon, and they have some determined sense qualities and weight. Trees share the inanimate qualities of their minerals and elements, but they also have properties that are proper to them, such as nutrition and growth. Generally speaking, a tree that stops growing upwards lacks perfection. Dolphins grow and have a certain weight, but their perfections consist in activities that involve sensation, desire, movement through water, and cooperative activity with members of their pod. When discussing the perfection of a species we look to its proper function. A dolphin’s weight or growth is important only to the extent that it affects the dolphin’s proper function. The animal’s goodness is relative to such a function.

Having previously argued in q. 54, art. 3, that goodness and badness are specific differences of habits, it is unsurprising to see the use of “good” as a specific difference that sets virtues apart from bad habits. The argument itself is based on the premise that virtue is a perfection of a power. Since evil is a defect and the good is perfect, the conclusion immediately follows. The only difficulty might be in the connection between the perfection of a power and goodness. Perhaps this connection is verbally more problematic in Latin, since “virtus” can be synonymous with “vis,” insofar as the latter word signifies strength or vigor. The first two objections note that there is a power to sin and that according to Scripture some are strong in the sense that they are able to drink large amounts of wine. Thomas easily responds to these objections by noting that virtue can be attributed to the bad in a metaphorical way. A thief can be called “virtuous” at stealing only to the extent that she is good at stealing. Such a thief is perfect as a thief, although imperfect as a human being. Similarly, a person might be strong in excessive drinking, but such virtue entails a defect of reason. This “virtue” is incompatible with human perfection.

Thomas’s understanding of the virtues depends on the thesis that good and bad habits are specifically distinct. Earlier in the Prima Secundae, q. 18, art. 2, he argues that good and bad acts are specifically distinct on account of their objects. In his discussion of the specific difference between good and bad habits, Thomas draws attention not to the object or the active principle so much as to the nature to which the habit is suitable. There are two kinds of suitability. First, the habit might be suitable or unsuitable to the agent’s own nature. Ordinary human virtues are concordant with human reason, whereas vices are discordant. But virtues can also make a subject suitable to a higher nature. Thomas argues that divine or heroic virtue is concerned with such suitability. We will return to Thomas’s understanding of divine or heroic virtue in Chapters 3 and 4.

Thomas’s position on the specific difference of good and evil habits draws attention to the way in which habits are principles of reasonable or unreasonable activity. An influential alternative to Thomas’s view will eventually be formulated by John Duns Scotus (d. 1308), who will argue that the goodness of a habit is not essential but consists only in a habit’s conformity to right reason.Footnote ⁷⁷ Thomas and his followers claim that if the order to reason changes then the habit itself changes. This difference draws attention to a fundamental disagreement concerning the very nature of such habits. Both Thomas and Scotus agree that someone who abstains from food for bad reasons might learn to abstain for good reasons or that someone who habitually sins with his concubine will cease to sin when he marries her. But for Thomas a habit is not a neutral quality that is made good or bad on the basis of an added order to reason. It is a kind of quality that has an essential conformity or lack of conformity to reason. The order of reason itself makes the habit what it is. Suppose that a person consistently performs reproductive acts with the same woman both before and after marriage. Although the natural species of the acts are the same, the human acts differ. Before marriage the agent commits fornication, and after marriage the agent renders the marriage debt. The habits consequently must change. The agent’s habit of unchastity cannot change into a habit of temperance once he is married simply because the woman with whom he was unchaste has become his wife.

Thomas’s discussion of habits provides the background for his general understanding of virtue as a good operative habit. Although Thomas’s emphasis on habit is Aristotelian, his order of discussion is not. Some aspects of Thomas’s treatment are clarified by considering that the Latin word for virtue differs in some respects from its English counterpart. Both the Latin “virtus” and the Greek “aretē” that it translates more generally signify any excellence and can consequently be easily applied to intellectual habits. Moreover, as we have seen, the Latin word is close to another Latin word, “vis,” which can refer to a power of the soul or to strength. Many of his arguments presuppose this connection of virtue with a power or perfection. When Thomas first defines virtue generally in the I-II, q. 55, he explains how Augustine’s definition of virtue includes the Aristotelian definition of virtue as a good operative habit. Only in subsequent questions does Thomas distinguish between moral virtues and intellectual virtues, including technical skill. The term “technical skill” is a possible but perhaps misleading, and to my ear awkward, translation of the Greek “techne” and Latin “ars.” Other possible translations might include “craft,” “art,” or “productive art.” These terms used in this way signify a habitual knowledge of how to make something. Horsemanship, bridle-making, and generalship are all “technical skills” in this sense. Since the term has a special meaning for Thomas and Aristotle, I will use “technical skill” for such knowledge.

It is at this point that we can see the way in which the Aristotelian definition of virtue allows Thomas to take into account how Aristotle’s insights on the nature of virtue are compatible with the definitions that were given by Thomas’s other sources, such as Cicero. It is important to consider Aristotle’s own argument for the thesis that virtue is a kind of habit in light of Thomas’s own commentary on it. Aristotle’s definition of moral virtue as a habit occurs after he had already distinguished moral virtue from intellectual virtue. In his Nicomachean Ethics, Book II, chapters 1–4, Aristotle states that moral virtue comes from action whereas intellectual virtue comes from study and teaching. Moral virtue differs from technical skills because its acts must be done with knowledge, for their own sake, and from a firm and stable character. Aristotle’s definition of virtue as a habit in the following chapters 5–6 is a definition of moral virtue and not of virtue in general.

According to Thomas, Aristotle gives in chapter 5 the genus of moral virtue as a habit and then in chapter 6 he provides the specific difference that distinguishes it from other habits. The argument for defining it as a habit depends on the premise that virtue, since it is a principle of operation in the soul, must be either a passion, a habit, or a power. Aristotelian passions include joy, sadness, love, and hate. Why is Aristotle so concerned with distinguishing habits from passions? Thomas gives comparatively less attention to this problem. Aristotle notes that virtues clearly involve passions. But by passion the agent is more moved than a source of action. The goodness of a virtuous action requires choice whereby the agent causes the act. We praise a person for what she does and not merely for what happens to her. Consequently, passions are in themselves neither good nor evil, whereas virtues are praised. Similarly, virtues cannot be powers of the soul, since we have the powers by nature. We do not acquire the powers of the soul through acting. If virtues are neither passions nor powers of the soul, then they must be habits. Aristotle’s argument for the thesis that virtue is a habit therefore depends on the praiseworthiness of virtue and the fact that it is acquired rather than natural.

In Book II, chapter 6, Aristotle describes the specific difference that distinguishes moral virtues from other habits. Thomas combines Aristotle’s statement here that virtue “perfects well the one having it, and renders his work well” with Aristotle’s definition in the older Latin translation of the De Caelo that “virtue is the peak of a power.”Footnote ⁷⁸ Thomas writes:

Aristotle himself illustrates this description with the examples of the virtue of an eye and of a horse. The eye’s virtue enables it to see well and makes it a good eye. The virtuous horse runs well, carries the rider, and performs under battle. It enables the horse to be a good horse insofar as the horse fulfills its role. Similarly, moral virtue makes humans good and it perfects human actions. Both Aristotle and Thomas use the word “virtue” (virtus, aretē) in these contexts in a wide sense. They do not think that habits can perfect the power of sight or the nonrational powers of horses. Nevertheless, there is a strength or excellence by which the subjects and their acts are good. Human acts are produced by powers that need habits to act well. A virtue is a habit that perfects powers in their production of operations that are themselves good and make the agent good.

Since habits are defined through their acts, and the humans are praised or blamed on account of their choices, it follows that moral virtue must be defined through choice (electio). This choice must concern a mean, since error in virtue can involve excess or deficiency. This mean is relative to the agent and not fixed. For instance, the appropriate diet for a giant wrestler would be different from that for a small, inactive person. This mean is good insofar as it is determined by reason. Consequently, Aristotle states that “virtue is a habit of choice, existing in a mean relative to us, determined by reason.” According to Thomas, Aristotle’s definition of moral virtue therefore gives a genus (“a habit”), an act that defines the habit (“of choice”), an object of this act (“existing in a mean relative to us”), and that which makes the act good (“determined by reason”). Aristotle’s definition of virtue was important for Thomas and his predecessors for understanding the way that all virtue is a habit, including intellectual virtue. But, as Thomas observes, Aristotle restricts this definition to moral virtue.

Habits Caused by God

After defining virtue in art. 1–3, Thomas follows his predecessors Philip and Albert in arguing for the superiority of the Augustinian definition of virtue as “a good quality of the mind, by which we rightly live, which no one uses badly, which God works in us without us.”Footnote ⁸⁰ Thomas’s discussion of this Augustinian definition can aid in thinking about the nature of the arguments in the previous three articles. Thomas states that Augustine’s definition includes the whole nature (ratio) of virtue since it includes all four causes of virtues, namely the formal, material, final, and efficient. Thomas makes a similar but less developed argument in his early In Sent., lib. 2, d. 27, q. un., art. 2.Footnote ⁸¹ But only in the Prima Secundae, q. 54, does he discuss this definition after having previously defined virtue as a good operative habit.

In the Prima Secundae, q, 55, art. 4, Thomas states that the definition is perfect because it mentions all four causes.Footnote ⁸² The formal cause of virtue is grasped in the genus and the specific difference. The definition’s description of virtue as a “quality” does not give the more proximate genus, which is habit, although it lists the genus to which habit itself belongs. The specific difference “good” distinguishes virtues from other habits. According to Thomas, the Augustinian definition also includes matter in its definition, although a general definition of virtue must exclude that matter which is the object that specifies an individual virtue. The relevant matter is the subject in which virtue adheres, which is the “mind.” The final cause of virtue must be operation, since virtue is an operative habit. Virtue’s end is distinguished from other operative habits by the fact that it is that “by which we rightly live, which no one uses badly.” Thomas follows Philip and Albert in holding that the stated efficient cause applies only to infused virtues, namely those “which God operates in us without us.” If this last clause is removed, then the definition applies to any virtue.

The Summa Theologiae and to a lesser extent the Commentary on the Sentences explain Augustine’s definition with reference to Aristotle’s four causes. In the De Virtutibus in Communi, q. un., art. 2, Thomas provides an alternative account that is based on Aristotle’s statement that virtue perfects the subject and the act.Footnote ⁸³ According to Thomas, there are two features required for the act’s perfection. First, the act that is produced must be good, and second the act’s principle must be incapable of producing a bad act. These two features are taken into account by that part of the definition which states “by which we live rightly, which no one uses wrongly.” This part of the definition refers to the act. The part of the definition that concerns the subject’s perfection has three parts: the subject, the perfection, and the way in which the virtue inheres in the subject. The subject is the mind, and the virtue inheres in the mind as a quality rather than as a passion. The perfection is indicated by the fact that virtue is a good quality, and not a vice or a habit that can be used well or poorly. For example, opinion is not a virtue since it can be erroneous, but science is a virtue and it does not err. Consequently, the agent’s perfection is taken into account by that part of the definition which states “a good quality of the mind.” He argues that when the clause about God’s work is removed, the Augustinian definition applies to acquired virtues, infused virtues, moral virtues, theological virtues, and even intellectual virtues.

Habits can be possessed naturally or be acquired through acts or be given by God. When discussing habits that are natural in the sense that they are possessed by nature, Thomas distinguishes first between the nature of the species and an individual nature.Footnote ⁸⁴ For instance, Socrates and Plato are naturally both risible because of their human nature, although only Plato has naturally broad shoulders. There is no difficulty in describing bodily dispositions as natural. For instance, Socrates might be naturally less beautiful but healthier than Plato.

Some operative habits seem to be natural to the species and not only to the individual, such as the ability to make such judgments as “The whole is greater than the part.” Thomas argues that these habits are only inchoately natural, since they require sense experience. For instance, without sense experience we would have no knowledge of what it is to be a whole and a part. On the other hand, the habit is natural to the extent that, once we possess the knowledge, we naturally and habitually make the judgment. The habit exists in the possible intellect that makes the judgment, but the developed habit presupposes the activity of the agent intellect whereby the intelligible species of the whole and the part are abstracted from phantasms.Footnote ⁸⁵

There is a parallel between the intellect’s assent to first principles and the will’s natural willing of happiness and the good in general, but the two acts differ to the extent that the will does not have in itself even inchoate virtue but a mere seed for acquiring virtue.Footnote ⁸⁶ On account of his individual nature person might more easily acquire virtues such as chastity or meekness, but the acquisition itself depends on free decision. This natural inclination that makes such acquisition easier resides in the individual’s bodily nature and not in the soul. The inchoate natural operative habit of the intellect is directly present in the power that it perfects, but inchoate natural appetitive virtue is a bodily disposition to actions that are performed by another power of the soul.

Other habits are not natural but must be acquired through acts or directly infused by God. For instance, dispositions such as sickness or beauty in some cases can be easily removed or restored through acts.Footnote ⁸⁷ Drinking poison might on its own take away health, and a powerful medicine on its own might restore it. Although the intellect has an inchoate natural habit of understanding first principles, other intellectual habits must be acquired. Strictly speaking, a habit of the possible intellect can be acquired through one act. For instance, by demonstrating the Pythagorean Theorem a scientific habit in the intellect can be engendered by which the agent firmly assents to it. But human reason relies on the inner senses, such as memory and the cogitative power. Insofar as they are in these lower apprehensive powers, such habits require multiple acts under normal circumstances and the assistance of other agents.Footnote ⁸⁸ A proof is better known if it is repeated and impressed on the memory. However, even accounting for such repetition, the habit of knowing the Pythagorean Theorem can be acquired more quickly than the habits of acting justly or temperately. Habits that concern contingent actions under normal circumstances require multiple acts and the assistance of other agents.Footnote ⁸⁹

Only some kinds of virtue are essentially the kinds of virtue that must be caused by God alone. Since God can cause effects directly without the assistance of secondary causes, any habit can be caused by God. He could produce the ordinary habits recognized by Aristotle directly without any of the agent’s own acts.Footnote ⁹⁰ Such causation by itself would not make specifically distinct habits. These habits miraculously caused by God would be the same as habits that are produced through acts. Although such acquired virtues could miraculously be caused by God, there are other virtues that can be caused by God alone. These latter virtues are called infused virtues because they cannot be acquired through human acts. These infused virtues are essentially supernatural, such as the theological virtues and, as we will see, the infused moral virtues. These essentially supernatural virtues dispose the agent to an end that exceeds human abilities. Only God can cause them. Human acts can dispose the agent to receive such an infused virtue and in some way aid in its increase, but they cannot cause an infused virtue.Footnote ⁹¹

Acts cause not only the existence but also the growth and even decrease of acquired operative habits. Habits grow sometimes by addition to what is included in their formal object, as when a person knows more scientific truths, and they also can increase in the way that they are possessed by their subjects.Footnote ⁹² Even already stable habits can increase. Growth in science or in virtue does not involve a replacement of already existing habits but an increase in formally the same habit. These habits are greater and smaller according to the way in which the subject participates in them. Thomas to some extent responds to Simplicius’s (d. 560) description of the Stoics in his own understanding of whether habits can be possessed in various degrees. According to the Stoics, some habits in themselves are capable of possessing degrees, such as the technical skills, whereas others are not, such as the virtues. On this account, a person might be more or less skillful at a task such as boatbuilding or farming, but everyone is equally just or temperate. Thomas addresses this thesis by drawing on the distinction between the habit’s nature and its presence in a subject. Thomas agrees with the Stoics that there is a difference between the technical skills and sciences, on the one hand, and virtues, on the other. A person might be more or less grammatical insofar as she knows more or less. Similarly, a boat builder might know more about the hull than about relevant hardware. In contrast, virtues are concerned with objects that cannot be so easily divided. Someone who is temperate will possess temperance with respect to any food or drink. According to Thomas, the difference between virtues and such other habits is that virtues are not the kinds of things whose objects can be possessed more or less on account of the extension of their objects. Nevertheless, all of these habits, including virtues, are capable of being more or less possessed by their subject. The Stoics erred in identifying virtue with only that virtue which is possessed in the highest way.

Some habits can increase by a kind of addition with respect to their object.Footnote ⁹³ For instance, one can increase the science of geometry by proving conclusions other than the Pythagorean. The science extends to more conclusions. Other habits are made more intense and perfect through the performance of their own acts, if the acts are equal to or greater than the virtue’s perfection. For example, by performing temperate acts the temperate agent disposes herself to temperance. Once a habit is acquired, it is stable. But a moral virtue’s stability requires many acts. Thomas writes, “first it begins to be imperfectly in the subject; and gradually it is perfected.”Footnote ⁹⁴

Some habits can be diminished or destroyed by contrary acts.Footnote ⁹⁵ Natural habits that exist in an incorruptible subject cannot be lost, since there are no contrary acts to the habit of knowing first principles in theoretical or practical reason or to the intelligible species that have been abstracted by the agent intellect. However, acquired habits can be diminished and even lost by imperfect acts of the same species or by acts that are directly contrary to the specific habit. For instance, the habit of farming can be lost through farming poorly, and good opinions can be lost through bad arguments. Moral virtues are lost through bad judgments, ignorance, and bad decisions that directly oppose them. For example, temperance can be diminished and lost through repeated acts of gluttony or excessive drinking.

Insofar as habits depend on the operations of the inner senses, they need to be used in order to be retained.Footnote ⁹⁶ For example, a science such as geometry is not diminished in the possible intellect over time, but it is diminished through disuse as it exists secondarily in the inner senses. It can also be diminished by an uncontrolled imagination. Furthermore, sciences and technical skills can be diminished or destroyed not only by contrary actions or disuse but also by damage or destruction to their subjects or even to subjects that they depend upon. For instance, sickness can take away science and technical skills insofar as they depend on the activity of the inner senses, including the particular reason. Even though science and technical skills are directly in the intellect, they are present in the inner senses in a secondary way, since they depend upon the cogitative power, imagination, and memory. If their sense organs are damaged or destroyed, these habits are in some way diminished or destroyed. To give an example, someone without the use of reason due to brain damage would be unable to exercise any intellectual habit. But not all habits depend on inner senses.

Only some virtues are of the kind that can be caused by God alone and not with the cooperation of secondary causes. Other virtues come from repeated acts. Moreover, acts preserve, increase, or weaken the habits. They are true efficient causes of some habits. Only certain habits are caused by God without secondary causes. Consequently, Lombard’s full definition of virtue applies only to such habits. However, the other aspects of his definition, which indicate the formal, material, and final causes of virtue, apply to all virtue, including the virtue that Aristotle discussed. We will return to the problem of whether any intellectual or moral virtues are possessed simply by nature and the precise way in which the different kinds of virtue are caused.

In the Primae Secundae, Thomas emphasizes that habits in general, and even in particular, can be defined by their four causes. Habits are distinguished from each other by their causes and by their order to either a nature or an operation. Since they are accidental forms that belong to the genus of quality, they are individuated by their active principles. Similar principles cause similar effects. For instance, temperate acts cause the habit temperance, and acts of geometry cause the habit of geometry. Dispositions such as health and beauty are individuated by the natures to which they are ordered. Operative habits are individuated by the objects of their acts. For instance, physics differs from metaphysics because it is about being insofar as being is movable or changeable, whereas metaphysics is about being as such. The same habit can be about materially the same object so long as there is a formal difference. The Aristotelian astronomer and physicist both prove that the earth is a sphere, although they do so by means of different demonstrations. The astronomer demonstrates this conclusion through the figures of eclipses, whereas the physicist does so through the observation that heavy objects move towards the center of the Earth. The same conclusion is therefore known through distinct habits. Unlike many later figures, Thomas contends that sciences are distinguished and unified by their formal objects. They are not collections of various propositions or intellectual species.

In the Summa Theologiae and the Commentary on the Sentences Thomas explains the Augustinian definition in terms of Aristotle’s doctrine of the four causes, and in the De Virtutibus in Communi he directly ties the Augustinian definition to Aristotle’s statement that virtue perfects the agent and the act. In these two works Thomas relies on two different Aristotelian texts. Nevertheless, in both he shows that when understood correctly, the Augustinian definition is compatible with both Aristotelian definitions. It is interesting that in these various texts Thomas approaches the definition from different angles without denying any of the assertions that are made in the parallel discussions.

Thomas’s understanding of the Augustinian definition of virtue has deep roots in Aristotle and the previous scholastic tradition. His principal Augustinian definition itself is formulated not so much by Augustine as by Peter Lombard. His discussion of this definition is indebted to Philip the Chancellor and Albert the Great, who argued that Augustine’s description of virtue as a quality is at bottom the same as Aristotle’s description of virtue of a habit and that Augustine’s description of virtue and its activity as caused by God applies only to infused virtues. They were among the first to show how both Aristotle and Christian writers such as Augustine could be helpful for moral philosophy and theology.

Thomas’s contribution is to develop this moral tradition more systematically and convincingly. In the Summa Theologiae, his discussion of virtue follows a lengthy set of questions on habits. Thomas’s discussion of habits incorporates newly available texts from Aristotle and arguably develops Aristotle’s thought beyond what Aristotle himself was able to articulate. For instance, Thomas’s distinction between the kinds of dispositions is not clearly stated by Aristotle although Thomas accurately describes a phenomenon that Aristotle recognized and needed to explain, namely the difference between dispositions such as health or beauty and dispositions that are imperfect virtues. Similarly, Thomas’s description of virtue as a good operative habit applies to all Aristotelian virtues and not merely to moral virtue. He provides a definition that is Aristotelian even though Aristotle himself had not arrived at it. In general, Thomas’s account is more developed than that of Aristotle even from an Aristotelian perspective. This enhanced Aristotelianism is able to take into account more clearly what Thomas inherits from his predecessors, such as the Augustinian definition of virtue.