Summa Theologiae

The Summa Theologiae is a Latin theological treatise composed by the Dominican friar Thomas Aquinas between roughly 1265 and his death in 1274. Written as a teaching text for theology students, it organizes Christian doctrine into a vast series of questions and objections answered through systematic argument. Although it is not a medical text, it has shaped the history of medicine in several durable ways: it provided the virtue-ethics framework that twentieth-century medical ethicists would revive for clinical practice; it gave a theological account of acedia (a condition resembling what later centuries would call melancholy or depression) that influenced how spiritual suffering was classified and treated; it integrated Avicenna’s metaphysics into Western Christian thought, cementing the scholastic synthesis on which university medicine depended; and its treatment of the body and sexuality established categories that structured medical-theological discourse throughout the medieval and early modern periods.

Context and Composition

Aquinas began the Summa Theologiae in Rome in 1265 and continued working on it until December 1273, when he stopped writing following what appears to have been a physical or mystical crisis. The text was left incomplete at the Third Part; a Supplement was later assembled from his earlier Commentary on the Sentences of Peter Lombard. The work is divided into three main Parts (with the Second Part subdivided into two), and proceeds through numbered questions (quaestiones), each containing objections, a main body (corpus articuli), and replies.

The institutional context shapes what the text is and what it is not. The Summa is not a medical work, and Aquinas was not a physician. He was writing within the university theology faculty at a moment when the newly available Aristotelian corpus, translated into Latin from Arabic along with the commentaries of Avicenna and Averroes, was transforming every field of knowledge. His project was to show that Aristotelian natural philosophy and Christian theology could be made coherent, and that reason and faith addressed overlapping rather than incompatible domains. The Summa Theologiae is the most complete expression of this project.

For the history of medicine, the relevant parts are concentrated in the Second Part: the Prima Secundae (first part of the Second Part) on moral psychology, the virtues, and the passions; and the Secunda Secundae (second part of the Second Part), which treats individual virtues and vices in detail, including the treatment of acedia at question 35.

Content Relevant to Medicine

The Summa Theologiae is relevant to the history of medicine under four headings: its analysis of acedia as a theological vice with clear psychological symptomatology; its systematic account of the virtues, especially prudence, justice, fortitude, and temperance, which later medical ethicists would apply to clinical practice; its incorporation of Avicennian metaphysics as part of the scholastic philosophical framework that undergirded university medicine; and its treatment of reproduction and sexual ethics in theologically modified but physiologically engaged terms.

None of these topics makes the Summa a medical text. But they make it a text that medicine could not ignore, and that shaped how physicians, moralists, and educators thought about the body, character, and care.

Acedia as Theological Vice

The most extensive engagement between the Summa Theologiae and what we might broadly call the history of psychiatric classification comes through Aquinas’s treatment of acedia in the Secunda Secundae, question 35.

Aquinas gave two formal definitions of acedia. The first is tristitia de bono divino: “sadness about spiritual good.” The second is taedium operandi: “disgust with activity.”(Nault, 2015) Nault’s close reading of these definitions reveals how much Aquinas built into each.

The first definition operates within Aquinas’s broader moral psychology of love. In his account, every loving movement of the soul passes through three moments: an intentional union or affective union (unio affectus), a desire (desiderium), and a real union or joy (gaudium).(Nault, 2015) Charity, understood not as sentiment but as a form of friendship (amicitia) between God and humanity, moves through this same arc, and the gaudium de caritate, the joy that springs from charity, is the anticipated real union with God.(Nault, 2015) Acedia is the sin against this joy. Aquinas deliberately aligns himself with Gregory the Great, for whom acedia was a form of sadness, but adds a new specification: acedia is not sadness in general but sadness at spiritual good specifically.(Nault, 2015)

Aquinas was aware of the obvious objection: why would anyone be sad at something good? His answer is that carnal, temporal, and limited goods appear more concrete and immediately attractive than spiritual good, so that on the interior scale of desire, spiritual good appears to weigh less.(Nault, 2015) The person experiencing acedia is not drawn to evil as such; they are drawn to false goods that displace the spiritual from first place.

Aquinas further distinguished gaudium from delectatio (pleasure). Delectatio is corporeal and natural; gaudium is spiritual, with a place for reason within it.(Nault, 2015) Nault, following Aquinas, identifies spiritual joy as the unerring criterion and barometer of the spiritual life: the anticipation of real union with God, a fruit of communion with a personal being rather than a feeling reducible to sensation.(Nault, 2015) Acedia opposes gaudium specifically, making it a theological vice rather than merely a natural failing, because it directly attacks the life of God in the soul.

The second definition, taedium operandi or disgust with activity, locates acedia at the interior heart of action. It is not an external obstacle; it is an obstacle within the will itself, a sluggishness that prevents action from reaching completion.(Nault, 2015) In this sense, Nault notes, acedia can be a mortal sin: not because of its content (which is sadness rather than any dramatic transgression), but because it can cut the person off from God at the very source of their acting, destroying charity in the soul.(Nault, 2015)

Aquinas also showed that acedia is opposed to all three theological virtues: to faith, insofar as it manifests as a lack of confidence in God’s grace; to hope, insofar as it crushes the desire that moves toward union; and to charity, insofar as it paralyzes action at the point where real union should be achieved.(Nault, 2015)

The daughters Aquinas assigned to acedia show its range. He divided them into two categories: sins of flight (despair, faint-heartedness, torpor with respect to commandments, rancor, and malice) and sins of compensation (uneasiness of the mind, curiosity, loquacity, restlessness of the body, and instability).(Nault, 2015) Among the sins of flight, the gravest is despair of beatitude: the conviction that God cannot grant one beatitude because one is not worthy of divine mercy. Aquinas identifies this as the sin against the Holy Spirit, the sin for which Christ declared there is no remission.(Nault, 2015)

The list of compensations has drawn particular attention from modern readers. Nault reads Aquinas’s catalogue of compensatory daughters (mental flightiness, curiosity, garrulousness, physical agitation, and activism) as directly applicable to contemporary culture, where the same daughters appear in full: the frenzy for novelty, the flight into speech, the compulsive restlessness of body, the busyness that leaves no time for contemplation.(Nault, 2015) This reading suggests that Aquinas’s classification in the Summa had diagnostic precision that extended well beyond the monastic context in which acedia first emerged.

One of acedia’s daughters, pusillanimity (faint-heartedness), is the vice opposed to magnanimity. It also attracted later commentary. Aquinas identified pusillanimity as the inability to believe in the greatness of the vocation to which God calls a person.(Nault, 2015) Ratzinger (later Benedict XVI) identified what he called a modern “false humility” (the refusal to believe in one’s own greatness as a child of God) as the contemporary form of this daughter-vice. The theological and the psychological here touch.

The question of how this classification relates to the history of melancholy is not simple. Nault observes that after Aquinas, acedia disappeared almost entirely from manuals of moral theology following the philosophical revolution of William of Ockham (ca. 1295–1350), who severed moral goodness from its intrinsic orientation toward the good and grounded it instead in external divine law.(Nault, 2015) Once virtue was defined primarily as obedience to law rather than as an inventive capacity for excellent acts, acedia, which had been defined relationally as a disruption of the friendship between God and the human soul, lost its structural place in moral theology. It reappeared in subsequent centuries in two transformed shapes: as sloth, lukewarmness, and negligence in prayer within spiritual literature; and as melancholy in secular literary tradition, from Petrarch to Baudelaire.(Nault, 2015) The medicalization of melancholy and the disappearance of acedia from systematic theology are thus historically connected, though the causal story is complex.

Nault also notes that acedia’s root, understood through Aquinas’s analysis, is the absence of the great love whose object is beatitude. The connection between this absence and despair is direct: “Aquinas showed clearly that the root of despair is to be sought in acedia. Acedia is a lack of love, the lack of the great Love; it shatters the impulse of hope and threatens to lead to the rejection of life itself.”(Nault, 2015) For the history of medicine, this matters because it keeps the clinical and the theological in conversation: what later medicine called depression, the Summa analyzed as a disruption of love and hope.

The list of Hugh of Saint Victor (d. 1141), which replaced Gregory the Great’s sadness with acedia and kept the number of capital sins at seven, was the list Aquinas worked from.(Nault, 2015) This lineage matters: Aquinas did not invent acedia’s place in the catalogue of vices, but he gave it the most philosophically rigorous analysis it had ever received.

Nault extends Aquinas’s analysis beyond the monastic context to apply to marriage. Because Aquinas defined acedia as the sin against the gaudium that results from union with the beloved and as disgust with the activity aimed at a communion of persons, the same analysis applies to marital communion: acedia in marriage is the temptation to leave the marital cell by withdrawing into self instead of giving self.(Nault, 2015)

The overall movement of Aquinas’s treatment in the Summa is from symptom to structure: from the descriptive account inherited from Evagrius and Cassian, through a theological analysis of what specifically is being resisted (the joy of union with God), to an account of what mortal form it can take (despair of beatitude). For Nault, this is Aquinas’s distinctive contribution: Thomas, “heir of the long patristic and monastic tradition, proves to be prophetic when he assigns to acedia a strategic position in our understanding of Christian action.”(Nault, 2015)

Virtue Theory and Medical Ethics

The sections of the Summa Theologiae treating the virtues (particularly the Prima Secundae questions on moral psychology, and the Secunda Secundae treatments of individual virtues) became foundational for a twentieth-century revival of virtue ethics in medicine. The primary channel was Edmund Pellegrino and David Thomasma’s The Virtues in Medical Practice (1993), which adopted the Aristotelian-Thomist definition of virtue as its framework, arguing that subsequent definitions had not improved on it.(Pellegrino, 1993)

Aquinas’s synthesis, as Pellegrino and Thomasma describe it, accepted the classical cardinal virtues (prudence, justice, fortitude, temperance) but gave special prominence to prudence as the bridge between moral and intellectual virtues.(Pellegrino, 1993) He enriched Aristotle’s phronesis (practical wisdom) into the concept of prudence (recta ratio agibilium, the right way of acting) extending its discerning capacity to cover the supernatural virtues of faith, hope, and charity alongside the natural moral and intellectual virtues.(Pellegrino, 1993) For Pellegrino and Thomasma, clinical judgment is “essentially an exercise of prudence, the ‘right way of acting,’ to use Aquinas’ definition of prudence, in a complex situation fraught with uncertainties.”(Pellegrino, 1993)

Aquinas’s treatment of justice in the Summa was developed further by connecting it to the theological virtue of charity, giving the social virtues an additional impulse toward altruism not present in classical Greek thought.(Pellegrino, 1993) In the medical context, Pellegrino and Thomasma read this as grounding the healing relationship not in contract or calculation but in love: justice rooted in charity requires the physician to suppress self-interest and to serve the patient’s good because not doing so would be to relapse from love of the other into love of self.

Aquinas’s treatment of fortitude in the Summa, following Aristotle, held that fearlessness is actually a vice (it eliminates the natural fear one should have when facing difficulty) and that virtue concerns what is both difficult and good.(Pellegrino, 1993) For modern medical ethics, this distinction matters: the physician who feels no fear when confronting institutional pressure or the risk of retaliation for speaking out is not courageous in the Thomistic sense. Courage requires feeling the difficulty and acting well despite it.

Aquinas’s account of temperance in the Summa extended to cover an unusually broad range of everyday virtues and vices: sobriety, abstinence, chastity, clemency, gentleness, modesty, and humility, understood as the virtue that guides daily human needs toward what he called “intelligent living.”(Pellegrino, 1993) Pellegrino and Thomasma expanded this for the medical context to cover the temptations of professional power and the inappropriate use of medical technology, calling it the taedium operandi of clinical practice in reverse: the lust for doing rather than the refusal to act.

A distinctive Thomistic claim, noted by Nault in a different context, is that virtues in the Thomist sense are not habits in the post-Ockhamite meaning: a virtue (habitus) is an inventive capacity for excellent acts that simultaneously makes the acting subject good, not a fixed routine.(Nault, 2015) This distinction mattered for Pellegrino and Thomasma because it kept virtue ethics responsive to particular situations: the virtuous physician is not the one who rigidly follows a procedure but the one who can improvise toward the good within an uncertain clinical encounter.

The Avicennian Dimension

One of the Summa Theologiae’s most significant roles in the history of medicine is indirect: it is the text through which Avicenna’s metaphysics received its most authoritative integration into Christian scholastic thought.

Gutas documents that Aquinas incorporated the Avicennian concept of God as Necessary Being as one of his five proofs for God’s existence in the Summa Theologiae; four of the five proofs are of Aristotelian origin, but the third (God as the source of all necessity) is manifestly Avicennian.(Gutas, 2016) In De Ente et Essentia Aquinas follows Avicenna’s essence-existence distinction throughout. Catholic scholars who have studied the relationship have concluded that Aquinas was far more indebted to Avicenna than was previously recognized, and Gutas quotes the judgment that “without the influence of Arabian peripatetism the theology of Aquinas is as unthinkable as his philosophy.”(Gutas, 2016)

The transmission path had been established a generation earlier. Albertus Magnus, Aquinas’s teacher, was the first scholastic to adopt Arabian logic in its entirety (which was substantially Avicenna’s logic) and Duns Scotus would later declare himself entirely in favor of the Avicennian position in metaphysics. But it was through Aquinas’s Summa that the synthesis acquired its canonical form in university theology.

For the history of medicine, this matters because the scholastic medical curriculum of the thirteenth century and after rested on an Aristotelian-Avicennian synthesis. Avicenna’s Canon of Medicine was the dominant clinical textbook at European universities through the sixteenth century, and the philosophical framework that made it authoritative was legitimized precisely by its place in the Thomistic synthesis. A physician trained in the thirteenth-century university was trained within a system whose philosophical foundations the Summa Theologiae had ratified. The Canon and the Summa were not in competition; they occupied different domains of a single intellectual structure.

Sexuality and the Body

Aquinas’s engagement with the physiology of reproduction and sexuality in the Summa Theologiae occurred at a particular moment: the Aristotelian rediscovery of the thirteenth century had brought a new account of generation into the universities, competing with Galenic two-seed theory. Aquinas worked out a position that navigated the theological requirements while engaging seriously with the physiological debate.

Jacquart and Thomasset document that Aquinas posited a special intermediate blood (distinct from both menstrual blood and semen) as the material substance of the embryo. This third substance allowed him to maintain that the Virgin Mary supplied pure material for the Incarnation while keeping the account structurally faithful to the Aristotelian form-matter framework, in which male semen supplies form and female matter receives it.(Danielle Jacquart and Claude Thomasset, 1988) The theological precision here required genuine engagement with Aristotelian reproductive physiology, and the result was an internally coherent position.

On sexuality classified as contra naturam, Aquinas followed Aristotle in placing the responsibility entirely on the moral agent rather than on temperament or physiology. Jacquart and Thomasset show that the consequence for medieval medicine was direct: physicians, working in the shadow of this framework, placed homosexuality “outside their competence” (categorizing it as neither illness nor temperamental defect) and the result was systematic self-censorship in medical literature.(Danielle Jacquart and Claude Thomasset, 1988) The Summa’s moral classification determined the limits of medical authority.

The Summa thus operated in sexual medicine through double channels: it offered a theological physiology of generation that physicians could work with (the intermediate blood theory), and it established moral boundaries that physicians were unwilling or unable to cross. Both channels shaped medical writing through the Renaissance.

Reception and Influence

The Summa Theologiae shaped the history of medicine primarily through two later episodes: the scholastic tradition it anchored, which structured university medical education through the sixteenth century; and the twentieth-century revival of virtue ethics in medical practice, which explicitly returned to the Thomistic framework.

Within scholasticism, the Summa gave university theology and philosophy a stable architecture into which Avicennian and Aristotelian natural philosophy could be fitted. The authority of Aquinas meant that the intellectual project of the Summa (the coherence of natural philosophy and Christian theology) was not simply a philosophical option but the dominant framework within which medicine, theology, and ethics were taught. The Canon of Avicenna achieved its final academic legitimacy partly through this ratification; as Garcia-Ballester has argued, it did not dominate the curriculum until the Aristotelian-Avicennian synthesis it represented was confirmed by the Thomistic program.

The later episode is equally significant for this encyclopaedia. Pellegrino and Thomasma’s The Virtues in Medical Practice returned directly to Aquinas as the source for a medical virtue ethics adequate to the contemporary clinical situation. Their argument was that the Aristotelian-Thomist definition of virtue (as an inventive capacity for excellent acts oriented toward the genuine good of the patient) provided a richer account of clinical practice than the principle-based ethics that had dominated bioethics since the 1970s. This argument did not succeed in replacing principle-based ethics, but it significantly expanded the vocabulary available to medical ethicists, and it kept the Summa in active scholarly conversation at the end of the twentieth century.

The acedia analysis represents a third, underrecognized line of influence. The Summa’s treatment of acedia was the most philosophically systematic account of the condition before it largely disappeared from formal moral theology after the thirteenth century. When twentieth-century scholars (Nault among them) sought to reclaim acedia as a concept with contemporary diagnostic relevance, the Summa was the primary philosophical resource. The overlap between acedia’s daughters and the symptom clusters of modern depressive and anxious conditions is suggestive, and the Summa’s structural account (sadness at spiritual good, disgust with activity, despair of beatitude) offers a framework for understanding suffering that differs meaningfully from both the biological and the cognitive-behavioral models.

Scholarly Assessment

Modern scholars who have read the Summa Theologiae for its relevance to the history of medicine tend to find three things: a moral psychology more subtle than its reputation, a physiological engagement more serious than expected, and a reception history more continuous than the standard narrative of medieval decline and early modern rupture suggests.

Nault’s reading of the acedia chapter in the Secunda Secundae (IIa-IIae, q. 35) shows that Aquinas worked within the full patristic and monastic tradition (from Evagrius through Cassian to Hugh of Saint Victor) while adding a philosophical precision about the structure of love that his predecessors lacked.(Nault, 2015) The two definitions (sadness about spiritual good; disgust with activity) are not redundant; they correspond to two different moments in the movement of love that charity completes. The analysis is tight, and Nault’s judgment is that it remains “prophetic.”(Nault, 2015)

Pellegrino and Thomasma’s judgment is that the Thomistic account of virtue has not been surpassed for the purposes of medical ethics: subsequent definitions have not improved on the essential notion.(Pellegrino, 1993) This is a strong claim, and one that remains contested by bioethicists working in other traditions. But the specificity of the Thomistic contributions (prudence as recta ratio agibilium, temperance extended to cover the intelligent use of daily needs, justice rooted in charity) has proved its durability by remaining in use.

Gutas’s study places the Summa Theologiae at the center of the most significant philosophical encounter between Christian Europe and Islamic philosophy in the medieval period: the absorption of Avicennian metaphysics into the scholastic synthesis.(Gutas, 2016) For the history of medicine, this means the Summa is not merely a theological document but a node in the transmission history of Greek-Arabic medical and philosophical knowledge into European learning.

Jacquart and Thomasset’s reading of Aquinas’s reproductive physiology reveals a theologian genuinely engaged with the medical debates of his time, arriving at solutions (the intermediate blood theory) that were theologically motivated but physiologically coherent.(Danielle Jacquart and Claude Thomasset, 1988) The Summa is, from this angle, a document of the medieval moment when theology and medicine shared assumptions about the body and worked out their differences within a common framework.

Human Notes

See Also

• thomas-aquinas
• acedia
• virtue-ethics
• scholastic-medicine
• avicenna
• canon-of-medicine
• anatomy-of-melancholy
• medical-ethics
• pellegrino-thomasma-virtues-1993