Summa Theologica

Summary

The Summa Theologiae, traditionally called the Summa Theologica, is Aquinas's unfinished synthesis of Christian theology, written, as its prologue says, for beginners who were confused by the disorder and repetition of existing textbooks. It contains some 512 questions divided into about 2,600 articles, each built on the same disciplined form inherited from university disputation. An article asks a yes-or-no question, lists objections to the view Aquinas will defend, cites an authority on the contrary, gives Aquinas's own answer, and then replies to each objection in turn. The form forces every position to be stated at its strongest before it is judged. The work has three parts, following the movement of all things from God and back to God through Christ. The First Part, which is the text stored in this library, begins by arguing that sacred doctrine is a science that uses reason while resting on revelation, since grace does not destroy nature but perfects it. It then asks whether God exists, opening with the objection that evil disproves an infinitely good God and answering with the five ways: arguments from motion, efficient causation, contingency, degrees of perfection and the governance of the world. Questions on God's simplicity, perfection, goodness, infinity, eternity, knowledge, will and power follow, then a treatise on the Trinity. The treatise on creation explains that the world was made from nothing and that evil is a privation of good, not a thing in its own right. Long questions on angels, pure intellects without bodies, are followed by the work of the six days and the treatise on man. Here Aquinas, following Aristotle, argues that the intellectual soul is the single form of the human body, not a separate substance lodged in it, that the soul's powers of growth, sense, imagination, memory and intellect form an ordered hierarchy, and that human understanding always depends on images drawn from the senses, so that injury to the brain or sleep impairs thought. He then considers the first man in the state of innocence and closes the First Part with God's government of creatures, including the influence of angels, demons and heavenly bodies on human beings. The Second Part, the longest, is a treatise on human action and ethics: happiness as the last end, voluntary acts, the passions of the soul, habits, virtues and vices, law (including the famous account of natural law), grace, and then the theological and cardinal virtues in detail. The Third Part treats Christ and the sacraments. Aquinas stopped writing in late 1273 in the middle of the questions on penance, after an experience that his companion Reginald of Piperno reported had made all his writing seem like straw. Reginald and others completed the work with a Supplement compiled from Aquinas's earlier commentary on the Sentences of Peter Lombard.

Plot or Argument

• The method of the article

  Each article poses a question, states objections, cites an authority to the contrary ('On the contrary'), gives Aquinas's answer ('I answer that') and replies to the objections. The structure models fair argument and is the key to reading the whole work.

• Part I, QQ. 1–26: sacred doctrine and the one God

  Theology as a science grounded in revelation but using philosophy; the five ways of proving that God exists; God's simplicity, perfection, goodness, infinity, immutability, eternity, unity, knowledge, will, providence and power.

• Part I, QQ. 27–64: Trinity, creation and angels

  Processions and persons in God; creation from nothing; evil as privation of good and its cause; the nature, knowledge, will and fall of the angels.

• Part I, QQ. 65–102: the six days and the treatise on man

  The created world; the soul as form of the body; the powers of the soul; how the intellect knows through sense images; the creation of man and woman in God's image; the condition of the first humans before the Fall.

• Part I, QQ. 103–119: divine government

  God's government of the world; how angels act on human intellect, will, imagination and senses; demons; the action of bodies and heavenly bodies on human beings, without imposing necessity on free will; human generation.

• Part I-II: the human act, passions, virtue, law and grace

  Happiness as the last end; voluntary action; the eleven passions of the soul, including love, desire, pleasure, sorrow, fear and anger, with their remedies; habits, virtues, vices and sin; eternal, natural, human and divine law; grace.

• Part II-II: the virtues in particular

  Faith, hope and charity; prudence, justice, fortitude and temperance with their parts and opposed vices, including discussions of just war, lying, suicide and acedia; states of life.

• Part III and Supplement: Christ and the sacraments

  The incarnation and life of Christ, the sacraments in general, baptism, confirmation, the Eucharist and penance; Aquinas stopped writing in the treatise on penance and the Supplement completes the plan.

Characters

• Thomas Aquinas, author and respondent

  Dominican master who answers each question, giving opponents' arguments a hearing before replying.

• Aristotle ('the Philosopher'), principal philosophical authority

  Source of Aquinas's physics, psychology and ethics, cited simply as 'the Philosopher'.

• Augustine of Hippo, principal theological authority

  Most cited Christian writer, often quoted in the 'On the contrary' and sometimes reinterpreted.

• Pseudo-Dionysius the Areopagite, authority on God and angels

  Neoplatonist Christian writer behind the hierarchy of angels and the language of divine names.

• Avicenna, Averroes and Maimonides, Islamic and Jewish interlocutors

  Philosophers whose views on intellect, creation and divine names Aquinas engages, adopts or rejects.

• Reginald of Piperno, companion and secretary

  Dominican friar who reported Aquinas's final silence and helped complete the Supplement.

Lessons

• State the opposing case at its strongest

  Every article begins with objections to Aquinas's own view, often powerful ones, such as the argument from evil against God's existence. Only then does he answer. The method is a lasting model of intellectual fairness and of thinking against oneself.

  • Why does Aquinas begin the article on God's existence with the problem of evil?
  • Does the objection-and-reply form make his conclusions more or less persuasive?
  • Where might this method improve contemporary public argument?

• Grace perfects nature rather than replacing it

  Aquinas holds that revelation completes rather than abolishes reason, so philosophy, natural science and medicine have their own integrity within theology. This principle let him absorb Aristotle and gave later Catholic thought a framework for engaging science.

  • What limits does Aquinas place on what reason can know about God?
  • How does this principle differ from views that see faith and reason as opposed?

• The soul is the form of the body

  Against the Platonic view that a person is a soul using a body, Aquinas argues that the intellectual soul is the single form of the human being. Thinking always needs sense images and the brain, so injury, sleep or illness can impair understanding, while the soul itself is not reducible to matter.

  • How does Aquinas's hylomorphism compare with Descartes's dualism and with modern physicalism?
  • What does his discussion of frenzy and lethargy suggest about how medieval thinkers understood brain injury?
  • Why does he insist that it is the whole man, not the soul alone, who understands?

• Influence without necessity

  Aquinas grants that heavenly bodies, humours and even angels and demons can move the passions and imagination, but denies that they compel the will. Most people follow their passions, so predictions about groups often come true, yet any individual can resist. The argument anticipates modern debates about biological influence and responsibility.

  • How does Aquinas reconcile astrology's apparent success with free will?
  • Is his distinction between general prediction and individual freedom useful for thinking about genetics or neuroscience?

Context

The thirteenth century saw the founding of the universities of Paris and Oxford, the arrival of Aristotle's complete works in Latin through translations from Greek and Arabic, and the rise of the mendicant Dominican and Franciscan orders. Aristotle's natural philosophy, read with the commentaries of Avicenna and Averroes, appeared to some theologians to threaten doctrines such as creation and personal immortality. Aquinas set out to show that Aristotelian philosophy, rightly understood, was compatible with Christian faith.

Composition

Aquinas began the Summa around 1265–66 while directing a Dominican house of studies in Rome, continued it in Paris (1268–72) and Naples, and stopped in December 1273 during the Third Part. The Supplement was compiled after his death from his commentary on the Sentences of Peter Lombard. The work circulated in manuscript and was first printed in the fifteenth century. The English translation by the Fathers of the English Dominican Province appeared in 1911–1925 (revised 1920s); the stored Project Gutenberg text contains only the First Part.

Reception

Some propositions associated with Aquinas were caught up in the Paris condemnations of 1277, but the Dominican order adopted his teaching and he was canonised in 1323. The Council of Trent consulted the Summa closely, and Pope Leo XIII's encyclical Aeterni Patris (1879) made Thomism the basis of Catholic philosophical education. In the twentieth century Jacques Maritain, Étienne Gilson and others developed neo-Thomism, and analytic philosophers have revisited Aquinas on mind, action and natural law.

Comparisons

• the-nicomachean-ethics

  The Second Part of the Summa rebuilds Aristotle's ethics of happiness, habit and virtue inside a Christian framework, adding infused theological virtues and a last end in the vision of God that Aristotle never imagined.

• city-of-god

  Augustine is the Summa's most quoted authority; Aquinas systematises Augustine's scattered teaching on evil as privation, providence and grace while replacing much of his Platonism with Aristotle.

• meditations-on-first-philosophy

  Descartes, trained by Jesuit Thomists, broke with the Summa's view of the soul as the form of the body and made mind and body two substances, a choice whose consequences for medicine and psychology are still debated.

• dialogues-concerning-natural-religion

  Hume's Philo attacks the argument from design and causal regress, the reasoning behind Aquinas's second and fifth ways; reading the two shows what changed when natural theology lost its Aristotelian physics.

• the-consolation-of-philosophy

  Boethius's account of eternity as the simultaneous possession of endless life, and his reconciling of providence with free will, are adopted directly in the Summa's questions on God's eternity and knowledge.

• the-anatomy-of-melancholy

  Burton cites the scholastics on the passions, demons and despair; his humoral account of melancholy shares Aquinas's assumption that bodily humours affect imagination without determining the will.

Quotes

For Students

A reading companion for classical Christian high school students. See the student guide.

Reading Guide

Watch for

• The five steps of every article: the question, the objections, On the contrary, I answer that, and the replies to objections. Before reading Aquinas's answer, try to say why each objection is strong.
• Part I, Question 1, Article 8, where Aquinas explains how sacred doctrine uses reason and says that grace does not destroy nature but perfects it. This principle governs how he uses Aristotle throughout.
• Part I, Question 2, Article 3, which opens with the objection from evil before laying out the five ways. Notice that the reply to the first objection comes back to evil after the proofs are finished.
• The treatise on man in Part I, Questions 75-89, especially Question 76 on the soul as the form of the body and Question 84 on how understanding depends on images from the senses, with the examples of frenzy, lethargy, sleep, and fever.
• Part I, Question 115, Article 4, where Aquinas grants that heavenly bodies can stir the passions but denies that they compel the will. Watch how he explains why astrologers' predictions about crowds often come true.

Key terms and names

Article

The basic unit of the Summa, a single yes-or-no question treated in a fixed order of objections, an authority on the contrary, Aquinas's answer, and replies. The work contains thousands of them grouped into questions.

Sacred doctrine

Aquinas's name in Question 1 for theology grounded in revelation. He argues that it is a true science because it reasons from principles God has revealed, as other sciences reason from principles they take from a higher science.

The five ways

The five arguments for God's existence in Part I, Question 2, Article 3, from motion, efficient causation, contingency, degrees of perfection, and the governance of things toward an end. Each ends by naming what all call God.

The Philosopher

Aquinas's title for Aristotle, whose works on nature, the soul, and ethics he cites constantly. Calling him simply the Philosopher shows how fully Aquinas accepted Aristotle as the master of natural reason.

Privation

The absence of a good that a thing ought to have, as blindness is the absence of sight in an eye. Aquinas argues in the treatise on creation that evil is a privation of good, not a substance made by God.

Form of the body

Aquinas's claim in Question 76 that the intellectual soul is not a separate thing lodged in the body but what makes this matter a living human being. It is the root of his view that the whole man, not the soul alone, understands.

Phantasm

A sense image held in the imagination. In Question 84 Aquinas argues that the human intellect always understands by turning to phantasms, which is why brain injury, sleep, or fever can disturb thought.

Seminar Questions

1. Comprehension Name the five parts of an article in the Summa, and identify each of them in Part I, Question 2, Article 3.
2. Comprehension State the five ways in your own words. What does each one begin from in the world we observe?
3. Comprehension In Question 84, what examples does Aquinas give to show that the intellect depends on bodily organs, and what does he say happens to judgment during sleep and fever?
4. Interpretation Why does Aquinas place the strongest objection, that evil disproves God, at the very start of the article on God's existence, and is his reply about God bringing good out of evil a full answer or the beginning of one?
5. Interpretation What does Aquinas mean when he says that grace does not destroy nature but perfects it, and how does that principle allow him to rely on Aristotle in a work of theology?
6. Interpretation If the soul is the form of the body and thinking needs phantasms, how can Aquinas also hold that the soul survives death? What tension does he have to manage?
7. Interpretation In Question 115 Aquinas says most people follow their passions and few are wise enough to resist them. How does this let him explain the success of astrologers without giving up free will?
8. Big Question Is it a mark of strength or of weakness in an argument to begin by stating the opposing case as powerfully as possible?

Faith Connections

• Romans 1:20 (Scripture)

  Paul says that God's invisible attributes are clearly seen through the things that are made. Aquinas cites this verse in Part I, Question 2, Article 2 as the authority for saying that God's existence can be demonstrated from his effects, which is exactly what the five ways attempt.

• Exodus 3:13-14 (Scripture)

  God names himself to Moses as I AM WHO AM. Aquinas uses this text as the On the contrary of the article on God's existence, so that the five ways are framed by God's own self-revelation even while they proceed by reason.

• Augustine, Enchiridion, chapter 11 (Church Fathers)

  Augustine writes that God, being supremely good, would not permit evil in his works unless he were able to bring good even out of evil. Aquinas quotes this in his reply to the first objection of Question 2, Article 3, which shows how he builds the Summa on Augustine as much as on Aristotle.

• Hume, Dialogues Concerning Natural Religion, Parts II-V and IX (Great Conversation)

  Hume's skeptic Philo attacks the argument from design and the argument from the need for a first cause, the reasoning behind Aquinas's fifth and second ways. Reading the two side by side shows which of Aquinas's premises depend on Aristotelian physics and which do not.

Logic and Rhetoric

Central argument: In the fifth way: we see that natural bodies lacking knowledge act always or nearly always in the same way so as to reach the best result, which shows they act toward an end not by chance but by design. Whatever lacks knowledge cannot move toward an end unless it is directed by a being with knowledge and intelligence, as an arrow is directed by the archer. Therefore some intelligent being exists by whom all natural things are directed to their end, and this being we call God. More broadly, the Summa argues that because grace perfects nature, reason working from the created world and revelation received in faith lead to one coherent truth.

Rhetorical device: procatalepsis (anticipating objections). Part I, Question 2, Article 3 opens with the objection that if God existed there would be no evil discoverable, but there is evil in the world, therefore God does not exist. Aquinas states the opponent's syllogism crisply before answering, and the whole Summa repeats this pattern in every article.

Debate: Resolved: Aquinas's five ways succeed in proving the existence of God.

Memory Work

Since therefore grace does not destroy nature but perfects it, natural reason should minister to faith as the natural bent of the will ministers to charity

Since God is the highest good, He would not allow any evil to exist in His works, unless His omnipotence and goodness were such as to bring good even out of evil

Writing Prompts

Essay: Write your own article in the form of the Summa on a question raised by Part I, such as whether a person who loses memory through illness is still the same person. Include at least two serious objections, an On the contrary, your answer, and replies, drawing on Questions 76 and 84.

Comparison with Dialogues Concerning Natural Religion: Aquinas's fifth way argues from the order of nature to an intelligent director, and Hume's Philo argues that such order proves far less than Aquinas claims. Reconstruct each side as formal premises and a conclusion, and argue which premise is decisive for the disagreement.

Medical Lens

The Summa is a foundational text for the history of the mind-body problem and of medieval psychology. Its account of the soul as form of the body, with an ordered set of powers (vegetative, sensitive, imaginative, memorial, intellectual), shaped medical and philosophical psychology into the early modern period. In the First Part Aquinas uses frenzy and lethargy as evidence that understanding depends on bodily organs, gives a humoral-vapour theory of sleep, dreams and fever-dreams, describes lucid dreaming, and explains hallucinations in the mad by disturbed spirits and humours before allowing angelic or demonic causes. The Second Part, not in the stored text, contains the fullest medieval treatise on the passions, including sorrow and its remedies (among them sleep, baths, weeping, the sympathy of friends and contemplation of truth, I-II, Q. 38), acedia as spiritual sorrow, and the classic natural-law argument against suicide (II-II, Q. 64, Art. 5). These passages remain reference points in debates on emotion, depression and the ethics of suicide; their framework is Aristotelian and theological, not clinical.

• I, Q. 76, Art. 1

  The intellectual soul as the form of the body and the single principle of nourishment, sensation, movement and understanding.

  Mind Body
• I, QQ. 78–79

  The powers of the soul: vegetative, external and internal senses (common sense, imagination, estimative power, memory) and intellect.

  Mind BodyDementia Memory
• I, Q. 84, Arts. 7–8

  Understanding depends on phantasms; lesions in frenzy and lethargy impair it; sleep, vapours, fever-dreams and partly lucid dreams explained physiologically.

  Madness PsychosisDementia MemoryDreams NightmaresSleep InsomniaFever Infection
• I, Q. 91, Art. 3

  The fitness of the human body: equable temperament, the largest brain relative to body size, upright posture, and the trade-off with smell and speed.

  Humoral MedicineAncient Medicine
• I, Q. 111, Arts. 3–4

  How angels or demons can move the imagination and senses, set against natural causes of dream-visions and hallucinations in disturbed humours.

  Madness PsychosisAltered StatesHumoral Medicine
• I-II, Q. 38 (not in stored text)

  Remedies of sorrow: pleasure, weeping, the sympathy of friends, contemplation of truth, and sleep and baths, which restore the body's natural movement.

  Melancholia DepressionPhilosophy AS TherapySleep Insomnia
• II-II, Q. 64, Art. 5 (not in stored text)

  Whether it is lawful to kill oneself: Aquinas's three arguments from natural self-love, the community and God's dominion over life.

  Suicide

Creative Prompts

• Dialogue

  Write a new article in Aquinas's form, with objections, an 'On the contrary', an answer and replies, on the question 'Whether a medication that changes mood changes the person.'

• Fiction

  Narrate Reginald of Piperno's account of the December day in 1273 when Aquinas stopped writing, as Reginald tries to persuade him to finish the treatise on penance.

• Essay

  Compare Aquinas's use of frenzy and lethargy in I, Q. 84, Art. 7 with modern evidence from brain injury and dementia. Does his view that intellect depends on, but is not identical to, bodily organs still have defenders?

• Classroom

  Have students reconstruct the five ways as formal arguments, then read Hume's Dialogues and identify which premises Hume attacks.

Further Reading

• Summa contra Gentiles, Thomas Aquinas

  His earlier synthesis, aimed at arguments from reason.

• Thomas Aquinas: His Personality and Thought, Jean-Pierre Torrell

  Published in English as Saint Thomas Aquinas, vol. 1: The Person and His Work.

• Aquinas, Edward Feser

  Introduction for modern readers.

• Aquinas on Human Nature, Robert Pasnau

  Detailed study of the treatise on man (I, QQ. 75–89).

• The Christian Philosophy of St. Thomas Aquinas, Étienne Gilson

• Medieval and Early Renaissance Medicine, Nancy G. Siraisi

  The medical theory of humours, spirits and faculties assumed by the Summa.