Five-minute digest
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.
Top 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.
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.
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.
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.
Verified Quotes
Frequently cited
“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”
“If, therefore, God existed, there would be no evil discoverable; but there is evil in the world. Therefore God does not exist”
Frequently cited
“I answer that,_ The existence of God can be proved in five ways”
“Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God”
Frequently cited
“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”
“For the soul is the primary principle of our nourishment, sensation, and local movement; and likewise of our understanding”
“For when the act of the imagination is hindered by a lesion of the corporeal organ, for instance in a case of frenzy; or when the act of the memory is hindered, as in the case of lethargy, we see that a man is hindered from actually understanding things of which he had a previous knowledge”
“If, however, the evaporation be somewhat less, phantasms appear, but distorted and without sequence; thus it happens in a case of fever”
“so that sometimes while asleep a man may judge that what he sees is a dream, discerning, as it were, between things, and their images”
“thus of all animals he has the least sense of smell. For man needs the largest brain as compared to the body”
“Indeed, the commotion of the spirits and humors may be so great that such appearances may even occur to those who are awake, as is seen in mad people, and the like”
“The majority of men follow their passions, which are movements of the sensitive appetite, in which movements of the heavenly bodies can cooperate: but few are wise enough to resist these passions”
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.
- I, QQ. 78–79
The powers of the soul: vegetative, external and internal senses (common sense, imagination, estimative power, memory) and intellect.
- 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.
- 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.
- 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.
- 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.
- 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.