Summa Theologiae (often called Summa Theologica)

1. Introduction

The Summa Theologiae (often called the Summa Theologica) is a large-scale scholastic treatise by Thomas Aquinas composed between about 1265 and 1273. Intended as a systematically ordered exposition of Christian doctrine, it gathers and organizes biblical material, patristic authorities (especially Augustine), and Aristotelian philosophy into a unified framework.

The work is divided into major parts and subdivided into questions and articles, each article addressing a tightly defined problem. Within this format Aquinas develops arguments on topics ranging from the existence and attributes of God, through human nature and ethics, to Christ, the sacraments, and eschatological “last things.”

Readers have often noted the Summa’s dual character: it is at once a theological textbook for students in the Dominican Order and medieval universities, and a philosophical resource that has been mined by later thinkers well beyond Aquinas’s original institutional setting. Its distinctive approach lies in combining rational argument, drawing heavily on Aristotle, with appeal to Scripture and church tradition, aiming to show how philosophical reasoning and revealed theology can be integrated without collapse of one into the other.

Because of its scope and internal organization, the Summa has served as a reference point for subsequent debates in metaphysics, philosophy of religion, and moral theory, as well as in confessional theology. Different intellectual traditions have appropriated it in divergent ways: some treat it primarily as a dogmatic authority, others as a philosophical toolbox, and still others as a historical document reflecting a particular 13th‑century synthesis of faith and reason. Later sections of this entry trace these themes through the work’s specific doctrines, method, and reception.

2. Historical and Intellectual Context

Aquinas wrote the Summa Theologiae within the milieu of 13th‑century Latin scholasticism, shaped by the institutional life of mendicant orders and universities such as Paris. The work reflects several converging developments in theology and philosophy:

2.1 University and Mendicant Milieu

The rise of universities created a structured curriculum in which theology was taught as a formal discipline. The Dominicans and Franciscans staffed many theology faculties, producing extensive commentaries on Peter Lombard’s Sentences. Aquinas’s Summa emerges as an alternative, more pedagogically streamlined synthesis of doctrine for students, especially within the Dominican studia.

2.2 Recovery of Aristotle

The 12th and 13th centuries saw a major influx of Aristotelian texts—on physics, metaphysics, psychology, and ethics—often mediated through Arabic and Jewish commentators such as Avicenna and Averroes. These texts provided systematic philosophical tools but also raised concerns about eternity of the world, the unity of the intellect, and determinism.

Aquinas’s project sits at the intersection of this Aristotelian revival and earlier Augustinian and Neoplatonic traditions. He employs Aristotle’s concepts of act and potency, causality, substance, and finality, while also drawing on Augustine’s teachings about illumination, grace, and the Trinity.

2.3 Theological Controversies

Several live controversies provide background to the Summa:

Within this context, the Summa presents a system in which philosophical reasoning is given a substantial role, yet is explicitly subordinated to sacred doctrine grounded in revelation, aiming to address these controversies in a constructive, pedagogical format.

3. Author and Composition

3.1 Thomas Aquinas

Thomas of Aquino (1224/5–1274) was a Dominican friar and theologian educated in Naples, Cologne, and Paris. A student of Albert the Great, he worked within the Dominican intellectual program to engage Aristotle and other non-Christian sources in the service of Christian theology. Aquinas produced biblical commentaries, philosophical treatises, disputed questions, and extensive commentaries on Aristotle and on Lombard’s Sentences.

Interpreters often stress that Aquinas wrote as a theologian whose principal task was to expound Christian doctrine for the church, even when he employed philosophical tools with exceptional rigor. The Summa Theologiae thus needs to be read in relation to his broader theological corpus and his responsibilities as a Dominican teacher and preacher.

3.2 Circumstances and Stages of Composition

Most scholars hold that Aquinas began the Summa around 1265, likely at the Dominican studium at Santa Sabina in Rome, continued it during his second Paris regency (1269–1272), and brought it with him to Naples in 1272–1273. He did not complete the work: the Tertia Pars breaks off after the treatment of penance, and later editors supplied a Supplementum mainly from his earlier commentary on the Sentences.

Key stages can be summarized as follows:

Aquinas reportedly ceased dictating the Summa after a mystical experience in December 1273, after which he regarded his writings as “straw” compared to what had been revealed to him. He died in March 1274 en route to the Council of Lyons. Later scholars debate the historical details of this episode, but it is generally accepted that it marks the abrupt end of the Summa’s composition.

4. Purpose and Audience of the Summa Theologiae

4.1 Stated Pedagogical Aim

In his prologue, Aquinas explicitly identifies the pedagogical purpose of the Summa:

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“We have considered that beginners in this doctrine are greatly hindered… because the truth which they ought to learn is put forward in various ways in different works… Therefore we intend… to set forth whatever belongs to the Christian religion in a way that is fitting to the instruction of beginners.”

— Thomas Aquinas, Summa Theologiae I, Prologue

The work is thus designed as an ordered, concise summary of sacred doctrine for “beginners” (incipientes) in theology, as distinct from advanced specialists producing extensive commentaries and disputed questions.

4.2 Primary Audience: Dominican and University Students

Most historians agree that Aquinas’s immediate audience consisted of Dominican friars in training and, more broadly, theology students in the emerging university system. The structure of the work parallels the needs of the curriculum: it starts with foundational doctrines about God and creation before moving to human actions, virtues, and finally Christ and the sacraments.

The Summa’s question–article format mirrors the procedures of disputations and lectio in medieval classrooms, enabling students to see opposing arguments, authoritative citations, and the master’s synthesis in a compact form.

4.3 Broader Programmatic Intentions

Interpreters differ on how far Aquinas intended the Summa to function beyond a teaching manual:

What is generally agreed is that the Summa is carefully arranged to guide readers into the interconnected whole of Christian doctrine, assuming some prior catechetical knowledge but systematically deepening it within a scholastic framework.

5. Structure and Organization of the Work

The Summa Theologiae is organized on multiple levels, from the macro-division of parts down to individual articles.

5.1 Major Parts

Aquinas divides the work as follows:

This progression reflects a doctrinal logic: from God and creation, through human action and moral life, to Christ and sacramental mediation, concluding with last things (in the Supplement).

5.2 Questions and Articles

Each part is divided into questions (quaestiones), which treat a thematic cluster, and each question is subdivided into articles (articuli). An article asks a narrowly focused question (e.g., “Whether God exists?”; “Whether law is something pertaining to reason?”).

The number of questions and articles is substantial:

Exact counts vary slightly by edition, but the overall pattern shows increasing detail in the moral and virtue sections, and a dense treatment of sacramental questions before the unfinished break.

5.3 Thematic Ordering

Within each part, Aquinas follows an internal order based on causal and teleological relations:

• In Prima Pars, God is considered first in himself, then as principle of creatures, followed by the hierarchy of created beings.
• In Prima Secundae, he moves from ultimate end (happiness) to human acts and habits, then to virtues, vices, law, and grace.
• In Secunda Secundae, each virtue is treated along a similar pattern: its nature, its acts, related gifts and beatitudes, opposing vices.
• In Tertia Pars, the order moves from the person of Christ to his work of salvation, and then to sacraments as instruments applying that work.

This layered structure allows the Summa to be read both linearly and consultatively, as a reference for particular doctrinal loci.

6. Scholastic Method and Question–Article Format

6.1 The Scholastic Method

The Summa exemplifies the scholastic method that developed in medieval universities. This method emphasizes:

• Careful distinction of questions.
• Systematic gathering of authorities (Scripture, Fathers, philosophers).
• Formal consideration of objections.
• A structured resolution through argument and synthesis.

It reflects classroom practices of disputatio (formal debates) and lectio (commentary on authoritative texts), translated into a written, highly organized literary form.

6.2 Structure of an Article

Each article follows a characteristic pattern:

1. Question (Utrum) – stated in yes/no or narrowly focused form.
2. Objections (Videtur quod non…) – a series of arguments for a position that Aquinas will ultimately reject, often from philosophical reasoning or authoritative texts.
3. Sed contra – a brief counter-assertion grounded in an authority (e.g., Scripture, Augustine, Aristotle).
4. Respondeo dicendum quod – the main body of Aquinas’s own answer, where he gives definitions, distinctions, and arguments.
5. Replies to objections (Ad primum, etc.) – point-by-point responses, reinterpreting or limiting the force of the objections in light of the respondeo.

This can be summarized:

6.3 Use of Authorities and Reason

Aquinas combines ratio (philosophical reasoning) and auctoritas (authority):

• Scriptural and patristic sources are decisive within sacred doctrine.
• Philosophical arguments (especially Aristotelian) are used where they can support or clarify truths about God, nature, and morality.

Scholars have debated how this method negotiates the relation between faith and reason. Some see it as harmonizing them; others argue it preserves strong asymmetry, with reason serving faith. The question–article format itself, however, is widely regarded as a transparent vehicle for presenting both contested positions and Aquinas’s resolutions in a logically ordered fashion.

7. Doctrine of God and the Five Ways

7.1 God in the Prima Pars

The Prima Pars opens with sacred doctrine as a science and then moves quickly to the question of God’s existence and nature (ST I, qq.2–26). Aquinas treats:

• Whether God exists.
• How God can be known by reason and by revelation.
• Divine simplicity, perfection, goodness, infinity, immutability, eternity, and unity.
• The names of God and the analogy of being.
• The Trinity as three persons in one essence.

The approach combines metaphysical analysis with interpretation of Scripture, following a clear path from the question “Is there a God?” to detailed attributes and intra-divine relations.

7.2 The Five Ways (Quinque Viae)

In ST I, q.2, a.3 Aquinas famously proposes five “ways” to show that God exists, arguing from features of the sensible world to a transcendent cause. They are often summarized as:

Aquinas identifies the terminus of these arguments with “that which all call God.” They rely on Aristotelian notions of act and potency, causality, and finality.

7.3 Interpretations and Debates

Interpretations of the Five Ways diverge:

• Traditional Thomist readings view them as demonstrative proofs from effects to a metaphysically necessary first cause, assuming a broadly Aristotelian worldview.
• Analytic philosophers of religion have reinterpreted the Ways as versions of cosmological and teleological arguments, assessing their validity under contemporary conceptions of causality and explanation. Some find them still defensible with reformulations; others argue that modern physics and metaphysics undercut key premises (e.g., about causal series).
• Historical critics contend that the Ways function more as programmatic starting points within a Christian framework already presupposing God, rather than as neutral proofs; proponents of this view emphasize their placement within a treatise of sacred doctrine.
• Theological interpreters focus on the integration of these arguments with Aquinas’s subsequent doctrine of God’s simplicity, transcendence, and knowability, arguing that the Ways are only the beginning of a larger theological approach that strongly qualifies what can be said about God.

Despite divergent assessments, the Five Ways remain among the most cited and debated elements of the Summa, frequently serving as a touchstone in discussions of natural theology.

8. Creation, Human Nature, and Providence

8.1 Creation ex nihilo

In the Prima Pars (qq.44–74), Aquinas develops a doctrine of creation in which God freely brings all things into being ex nihilo (out of nothing). Creation is not a temporal change from one state to another but a dependence of all being on the first cause at every moment. Aquinas distinguishes:

• God as first cause of being.
• Creatures as secondary causes, truly operative but dependent.

He also addresses the order of creation, the six days of Genesis, and the hierarchy of beings, including angels and the material world.

8.2 Human Nature: Body, Soul, and Powers

A substantial portion of Prima Pars (qq.75–102) treats human beings. Key elements include:

• The human soul as the substantial form of the body: a single principle that makes a living human being.
• The soul’s immateriality and immortality, drawn from Aristotelian psychology but modified to affirm personal survival after death.
• Distinction of powers of the soul: intellect, will, sense faculties, and appetites.

Aquinas portrays humans as rational animals whose intellectual and volitional capacities ground moral responsibility and openness to God.

8.3 Providence, Governance, and Evil

Later questions (qq.103–119) discuss divine providence and governance:

• God’s providence is the plan by which he orders all things to their ends.
• Governance is the execution of this plan in time, using created causes and contingent events.

A perennial issue is the place of evil:

• Aquinas argues that evil is a privation of good rather than a positive substance.
• God permits evil for the sake of greater goods within the overall order.

Interpretations vary:

Aquinas also addresses predestination and divine concurrence, seeking to affirm that God is the first cause of all good actions without negating creaturely agency. Debates over these issues later become central fault lines within Thomist and broader Christian theology.

9. Moral Theology: Happiness, Virtue, Law, and Grace

The Prima Secundae provides Aquinas’s general framework for moral theology, connecting human action to ultimate beatitude, virtue, law, and divine assistance.

9.1 Happiness and the Human End

In ST I–II, qq.1–5, Aquinas argues that every human action aims at some good, ultimately ordered to a last end. He concludes that true and perfect happiness (beatitudo) consists not in created goods (wealth, pleasure, honor, power) but in the beatific vision of God. Natural human capacities can desire this end but cannot attain it by their own power.

9.2 Human Acts, Passions, and Habits

Subsequent questions analyze:

• Human acts as voluntary, rational operations subject to moral evaluation.
• Passions as movements of the sensitive appetite, neither good nor evil in themselves but morally qualified by reason’s rule.
• Habits as stable dispositions, including virtues and vices.

This psychological analysis undergirds Aquinas’s virtue ethics and his account of moral responsibility, intention, and circumstances.

9.3 Virtue and Vice in General

Aquinas distinguishes:

• Intellectual and moral virtues, following Aristotle.
• Acquired virtues formed by repeated acts.
• Infused virtues given by God, orienting us to supernatural ends.

He lays out the cardinal virtues (prudence, justice, fortitude, temperance) as principles organizing moral life.

9.4 Law: Eternal, Natural, Human, Divine

In qq.90–97, Aquinas presents his influential doctrine of law:

This framework has been widely discussed in moral and legal philosophy, with proponents highlighting its grounding of moral norms in human nature, and critics questioning its assumptions about teleology and a fixed human essence.

9.5 Grace

In qq.109–114, Aquinas treats grace as a gratuitous divine gift that heals and elevates human nature. He distinguishes:

• Habitual (sanctifying) grace vs. actual grace.
• Grace’s role in justification, merit, and perseverance.

Debates among later interpreters focus on how Aquinas balances human cooperation with grace and divine initiative, with differing schools (e.g., Bañezian, Molinist, nouvelle théologie) emphasizing various aspects of his account.

10. Theological Virtues and Christian Life

In the Secunda Secundae, Aquinas gives detailed treatments of individual virtues, beginning with the theological virtues that directly order human beings to God.

10.1 Nature of Theological Virtues

In ST II–II, q.1, a.1, Aquinas defines theological virtues as habits:

• Whose object is God himself.
• Which are infused by God, not acquired by human effort.
• Which direct humans to a supernatural end beyond natural capacities.

The three theological virtues are faith (fides), hope (spes), and charity (caritas) (ST II–II, q.62).

10.2 Faith

Faith is treated in qq.1–16:

• Defined as an infused habit of the intellect by which we assent to divine truth on God’s authority.
• Distinguished from knowledge and opinion.
• Examined in relation to heresy, unbelief, and the confession of faith.

Interpreters debate whether Aquinas’s account leans more toward voluntarist (will-centered) or intellectualist (intellect-centered) conceptions of faith. Aquinas himself describes faith as involving both will (consent) and intellect (assent).

10.3 Hope

Hope (qq.17–22) is:

• A virtue of the will by which one trusts in God for future, difficult but attainable eternal happiness.
• Distinguished from presumption and despair.

Hope presupposes faith and requires charity for full perfection. It shapes Christian attitudes toward suffering and uncertainty.

10.4 Charity

Charity (qq.23–46) is central in Aquinas’s moral theology:

• Defined as the friendship of the human person with God, grounded in God’s love.
• Considered the form of all virtues, giving them orientation toward God.
• Expressed in love of God and neighbor, including self-love rightly ordered.

Aquinas analyzes related topics such as joy, peace, mercy, and the order of charity (whom we should love most and in what way).

10.5 Gifts of the Spirit, Beatitudes, and Christian Life

In qq.8–9 and qq.68–70, Aquinas connects virtues with:

• Gifts of the Holy Spirit, which perfect the soul for prompt responsiveness to divine motion.
• Beatitudes of the Sermon on the Mount, considered both as acts flowing from virtues and as foretastes of future happiness.

Different traditions draw various emphases from this material:

The overall picture presents Christian life as a graced participation in the divine life, structured by faith, hope, and above all charity.

11. Christology and the Incarnation

The Tertia Pars begins with an extended treatment of Christology, addressing the mystery of the Incarnation and the person and work of Christ.

11.1 The Fittingness and Necessity of the Incarnation

In qq.1–2, Aquinas asks whether it was fitting for God to become human and whether the Incarnation was necessary for human salvation. He distinguishes:

• Absolute necessity, where no other means are possible.
• Conditional necessity, given God’s chosen way of saving.

Aquinas argues that while God could have saved humanity in other ways, the Incarnation is supremely fitting because it manifests divine goodness, provides a mediator who is both God and man, and offers a pattern of virtue and union with God.

11.2 Hypostatic Union: One Person, Two Natures

Central to his Christology (qq.2–6) is the doctrine of the hypostatic union:

• In Christ there is one divine person (the Word, the Son) subsisting in two natures, divine and human.
• The human nature is complete (body and rational soul) but does not constitute a separate human person.
• The union is not by mixture or confusion of natures, but by the person of the Word assuming human nature.

Aquinas uses Aristotelian metaphysics to articulate this Chalcedonian formula, distinguishing between nature, person, and suppositum.

11.3 Properties and Knowledge of Christ

Subsequent questions examine:

• Christ’s knowledge (qq.9–12): Aquinas attributes to Christ the beatific vision, infused knowledge, and acquired knowledge, while insisting on real human learning experiences.
• Christ’s will and graces (qq.13–19): the harmony of a human will perfectly aligned with the divine will.
• The communicatio idiomatum (communication of idioms): how properties of each nature can be predicated of the one person (e.g., “God suffered,” “this man created the world”) without confusion.

Interpretations differ on how Aquinas balances Christ’s full humanity with his divine knowledge and impeccability. Some emphasize the exemplar role of a genuinely human life; others stress the metaphysical priority of the divine person.

11.4 Passion, Death, and Merits of Christ

In qq.46–49, Aquinas analyzes Christ’s passion and death:

• As an act of obedience and love, meriting salvation for humanity.
• As satisfaction for sin, sacrifice, and efficient cause of grace.

Later theological debates, particularly about atonement theories, have engaged his account of how Christ’s passion operates as cause of our salvation, some highlighting satisfaction and merit, others stressing love, solidarity, or victory over evil as developed further traditions.

12. Sacramental Theology and the Eucharist

After Christology, the Tertia Pars turns to sacraments as instruments by which Christ’s saving work is applied to individuals.

12.1 Sacraments in General

In qq.60–65, Aquinas treats sacraments as:

• Visible signs of invisible grace.
• Instituted by Christ.
• Instrumental causes that not only signify but also effect grace, by divine power.

He enumerates seven sacraments—baptism, confirmation, Eucharist, penance, extreme unction, orders, and matrimony—arguing for their fittingness and distinct purposes.

12.2 Causality and Efficacy

Aquinas analyzes sacramental causality using Aristotelian categories:

• Principal cause: God (and, in a special sense, Christ’s humanity).
• Instrumental cause: sacramental signs and rites.
• Disposition of the recipient: necessary for fruitful reception, though sacraments work ex opere operato (by the work performed), not merely by the minister’s or recipient’s subjective state.

Different theological traditions have interpreted this “instrumental causality” variously—as strongly objective efficacy, as relationally symbolic, or as needing to be rethought in light of contemporary semiotics.

12.3 The Eucharist and Transubstantiation

The treatment of the Eucharist (qq.73–83) is among the most influential:

• Aquinas affirms the real presence of Christ’s body and blood under the appearances of bread and wine.
• He articulates the doctrine of transubstantiation (q.75): the substance of bread and wine is converted into the substance of Christ’s body and blood, while accidents (sensible properties) remain without a subject.

Key points include:

12.4 Interpretations and Critiques

Interpretations vary:

• Catholic and many Orthodox theologians have drawn heavily on Aquinas to articulate Eucharistic doctrine, sometimes adapting his metaphysical vocabulary.
• Reformation traditions often accepted real presence in some form but rejected transubstantiation as explained via substance–accident metaphysics; they have critiqued the conceptual framework as outdated or obscure.
• Contemporary philosophers and theologians debate whether Aquinas’s account can be restated using more current metaphysical models (e.g., events, relational ontology) or whether it depends inextricably on a classical substance ontology.

Nonetheless, his carefully worked-out Eucharistic theology remains a standard reference for sacramental thought.

13. Eschatology: Last Things and the Beatific Vision

The Summa’s treatment of eschatology is completed in the Supplementum, compiled posthumously from Aquinas’s commentary on the Sentences. It addresses individual and general “last things,” culminating themes signaled earlier in discussions of happiness and grace.

13.1 Death, Judgment, Heaven, and Hell

The Supplement discusses:

• Death as separation of soul and body and entry into particular judgment.
• Hell and punishment of the damned.
• Purgatory as purifying temporal punishments for the saved.
• Heavenly glory and the hierarchy of the blessed.

These treatments align with medieval Catholic doctrine, using Aquinas’s metaphysics and moral theology to explain the nature of post-mortem states, degrees of punishment and reward, and the resurrection of the body.

13.2 Resurrection and General Judgment

Questions on the resurrection explore:

• Identity of the resurrected body with the earthly body.
• Qualities of glorified bodies (impassibility, subtlety, agility, clarity) for the blessed.
• The general judgment as public manifestation of God’s justice.

Aquinas’s positions engage patristic precedents while employing Aristotelian hylomorphism to explain bodily identity and transformation.

13.3 Beatific Vision

The beatific vision is central:

• Already anticipated in Prima Secundae (on happiness), it is elaborated in the Supplement as direct intuitive knowledge of God’s essence granted to the blessed.
• The vision fulfills natural desire for God while surpassing natural powers; it requires light of glory, a created participation enabling finite intellects to see the infinite.

Interpreters have approached this doctrine variously:

Aquinas also addresses degrees of beatitude, the relation between vision and love, and the eternal fixity of the blessed and the damned, all within his broader framework of grace and free choice.

14. Famous Passages and Influential Doctrines

Several specific passages and doctrines from the Summa Theologiae have exerted outsized influence in theology and philosophy.

14.1 The Five Ways (ST I, q.2, a.3)

The concise presentation of five arguments for God’s existence has become a classic reference point in natural theology. They are frequently anthologized and adapted in later philosophical argumentation, sometimes independently of their original theological setting.

14.2 Names of God and Analogy (ST I, q.13)

Aquinas’s doctrine that predicates such as “good,” “wise,” and “being” apply to God and creatures analogically—neither in exactly the same sense nor in wholly different senses—has shaped discussions of religious language. Supporters see it as avoiding both univocal anthropomorphism and empty equivocity; critics have worried about its clarity and viability in modern semantic theories.

14.3 Treatise on Law and Natural Law (ST I–II, qq.90–97)

The systematic account of law has significantly influenced Western moral and legal thought:

• The concept of natural law as participation in eternal law is central to Catholic moral theology.
• Modern natural law theorists (e.g., John Finnis) have developed philosophical versions inspired by Aquinas while revising elements of his metaphysics.
• Critics argue that appeals to natural law may mask culturally contingent norms or rest on contested claims about human nature and teleology.

14.4 Happiness and Beatific Vision (ST I–II, qq.1–5, esp. q.3, a.8)

Aquinas’s argument that ultimate human happiness lies in seeing God’s essence, not in any created good, provides the conceptual keystone for his ethics and eschatology. It has influenced later Catholic spirituality and has been both appropriated and questioned in contemporary virtue ethics and philosophical theology.

14.5 Doctrine of Transubstantiation (ST III, q.75)

His careful articulation of transubstantiation, using substance–accident categories, has become the standard scholastic formulation of Roman Catholic Eucharistic doctrine. It features prominently in confessional documents (e.g., Council of Trent) and continues to frame ecumenical dialogues and philosophical debates about presence, change, and symbolism.

14.6 Virtue Ethics and Charity (ST II–II, esp. qq.23–46)

The extensive treatment of virtues, especially charity as the form of the virtues, has made the Summa a major source for contemporary virtue ethics. The integration of Aristotelian virtue theory with a theological account of grace and supernatural ends is often cited as a distinctive contribution.

These and other loci are frequently studied on their own as self-standing doctrines, while scholars also emphasize their place within the Summa’s larger architectonic of God, creation, and salvation.

15. Reception, Criticisms, and Debates

The Summa Theologiae has had a long and complex reception, with shifting evaluations across periods and traditions.

15.1 Medieval and Early Modern Reception

In the late Middle Ages:

• The Summa gradually became a central reference within Thomist circles, especially Dominicans.
• Other schools (Franciscan/Scotist, nominalist) engaged critically with Aquinas, disputing, for example, his doctrines of divine simplicity, analogy, and grace.

In the early modern period, Thomist theologians defended Aquinas’s positions in controversies about predestination, grace and free will (e.g., De Auxiliis debates), and sacramental theology.

15.2 Protestant and Post-Reformation Critiques

Reformation thinkers often:

• Appreciated aspects of Aquinas’s doctrine of God and occasionally his ethics.
• Criticized the Summa’s sacramental and ecclesiological doctrines, and its use of Aristotelian metaphysics.
• Questioned the nature–grace schema, arguing it risked granting too much autonomy to natural reason and moral ability.

In later Protestant scholasticism, Aquinas’s framework sometimes served as a foil for alternative systems, even as specific arguments (e.g., on God’s existence) were selectively adopted.

15.3 Enlightenment and Modern Philosophy

During the Enlightenment and after:

• The Aristotelian metaphysics underlying much of the Summa came under scrutiny.
• Philosophers influenced by empiricism, Kantianism, or modern science often viewed doctrines such as substantial forms, final causes, and transubstantiation as incompatible with newer paradigms.

Some modern philosophers of religion, however, have revisited Aquinas’s arguments (especially the Five Ways and the doctrine of God), reformulating them within analytic frameworks or using them as historical benchmarks.

15.4 Neo-Thomism and 20th-Century Debates

The 19th–20th centuries saw a neo-Thomist revival, especially within Roman Catholicism, with papal documents recommending Aquinas as a model. Neo-Thomist scholars systematized and sometimes “manualized” the Summa’s doctrine.

Critiques arose from:

• Nouvelle théologie theologians, who argued that some neo-Thomist readings were overly rationalistic or abstract, underplaying biblical and historical dimensions.
• Existential and personalist philosophers, who questioned impersonal metaphysical categories and the priority given to essences and natures.
• Feminist and liberation theologians, who have critiqued, among other things, gender assumptions and social hierarchies embedded in the work and its reception.

15.5 Contemporary Discussions

Current debates involve:

Across these discussions, the Summa serves both as an authoritative source within some traditions and as a critical interlocutor in broader philosophical and theological debates.

16. Legacy and Historical Significance

The Summa Theologiae has played a major role in shaping Western Christian thought and, indirectly, broader intellectual history.

16.1 Institutional and Doctrinal Influence

Within Roman Catholicism:

• The Summa became a standard teaching text in seminaries and universities, especially from the late Middle Ages onward.
• Doctrinal formulations at councils (e.g., Trent, Vatican I) and in magisterial documents frequently draw on Aquinas’s concepts, especially regarding grace, sacraments, Eucharist, and natural law.
• Papal encyclicals (e.g., Aeterni Patris) have recommended Aquinas as a preeminent guide, consolidating the Summa’s canonical status.

16.2 Impact on Philosophy and Ethics

Philosophically, the Summa has:

• Influenced metaphysics (being, essence and existence, causality) and philosophy of religion (arguments for God, divine attributes).
• Contributed to virtue ethics, where Aquinas’s integration of Aristotelian virtue, Christian charity, and a teleological account of human flourishing remains a major resource.
• Informed natural law theory in legal and political philosophy, shaping debates about human rights, justice, and the relation between morality and positive law.

Different schools have selectively appropriated or criticized these elements, but the Summa often serves as a key reference in reconstructing pre-modern thought.

16.3 Ecumenical and Interreligious Dialogue

The Summa has played roles in:

• Ecumenical dialogues, where Aquinas’s formulations of doctrines such as justification, Eucharist, and grace are engaged by Protestant, Orthodox, and Catholic theologians seeking convergences and clarifying disagreements.
• Interreligious discussions, particularly with Jewish and Islamic philosophy, given Aquinas’s engagement with figures like Maimonides and Averroes and his use of shared Aristotelian categories.

16.4 Modern Reassessments

Contemporary scholars approach the Summa with varied aims:

Across these approaches, the Summa Theologiae is widely regarded as one of the most ambitious and influential attempts to articulate a comprehensive synthesis of Christian doctrine and philosophical reasoning, continuing to serve as a touchstone for reflection on the relations between faith, reason, and moral life.