Summa Theologica: A Beginner’s Guide

The Summa Theologica, written by Saint Thomas Aquinas—known as the Angelic Doctor—between 1265 and 1273, is one of the most important works of Christian theology. It represents the culmination of scholastic thought and has become a foundational intellectual pillar of the Catholic Church.

Far from being an outdated or purely historical text, the Summa Theologica remains a living source of wisdom. Its lasting importance was formally affirmed by the Church’s Magisterium, most notably in the encyclical Aeterni Patris, issued by Pope Leo XIII in 1879. In this document, the Pope promoted the renewal of Christian philosophy based on the thought of Saint Thomas Aquinas and emphasized that his work offers a model expression of the harmony between faith and reason.

For readers approaching the Summa Theologica for the first time, it is important to know that it was originally conceived as a manual for beginners—that is, for those taking their first steps in the study of the truths of the faith.

Do you want to read the Summa Theologica but feel overwhelmed by its size and structure? This beginner’s guide is meant to help you navigate the work and understand it with clarity and confidence.

Who was Saint Thomas Aquinas?

Saint Thomas Aquinas was a 13th-century Dominican friar, theologian, and philosopher, widely regarded as one of the greatest masters of Catholic thought. He was born in 1225 at the castle of Roccasecca, in southern Italy, into a noble family. From an early age, he showed a strong inclination toward study and the religious life.

Despite his family’s initial opposition, St. Thomas Aquinas entered the Order of Preachers, where he was able to fully develop both his intellectual and spiritual vocation. During the period in which his family attempted to dissuade him from religious life, Thomas was held against his will. According to tradition, on one occasion they sent a woman to tempt him and persuade him to abandon his calling. Thomas responded by seizing a burning ember and chasing her from the room. He then knelt in prayer, asking God for the grace of purity. From that moment on, he became known for his chaste life and remarkable self-mastery.

Educated at the leading schools of his time, he became a disciple of St Albert the Great and quickly distinguished himself by his ability to unite philosophical rigor with the depth of faith. Tradition recounts that, both as a student and later as a teacher, St Thomas Aquinas was a quiet and humble man. Because of his reserved demeanor and large build, his fellow students mockingly nicknamed him “the Dumb Ox.” Upon hearing these taunts, his teacher replied with a now-famous remark: “You call Thomas the Dumb Ox, but his bellowing will one day be heard throughout the whole world.” In time, the depth and influence of Thomas’s thought fully confirmed these words.

Living in an era marked by the rediscovery of Aristotle, Saint Thomas Aquinas succeeded in integrating classical philosophy with Christian doctrine. In doing so, he demonstrated that reason and faith are not opposed, but rather illuminate one another. His teaching was marked by clarity, order, and a sincere desire to lead others to the truth, combined with humility before mystery and fidelity to revealed Truth.

Toward the end of his life, after a profound mystical experience while celebrating Holy Mass, St. Thomas Aquinas left the Summa Theologica unfinished. When one of his brothers asked why he no longer continued writing, he replied with humility: “I cannot go on. All that I have written seems to me like straw, compared to what has been revealed to me.”

The Church quickly recognized both the greatness of his intellect and the holiness of his life. He came to be known as the Angelic Doctor for the loftiness of his doctrine and the purity of his teaching. He was canonized in 1323 and proclaimed a Doctor of the Church in 1567.

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Summa Theologica for beginners

Why did Saint Thomas Aquinas write the Summa Theologica?

The origin of the Summa Theologica is closely connected to a problem in the teaching of theology that Saint Thomas Aquinas identified in the universities of his time. In the thirteenth century, theological formation relied primarily on commentaries on Peter Lombard’s Sentences. According to the Angelic Doctor, this method often led to confusion, due to the disorderly presentation of topics and the unnecessary repetition of secondary questions.

In response to this situation, St. Thomas Aquinas conceived the Summa Theologica as a clear, concise, and well-ordered exposition of Christian doctrine. His aim was not to mirror the pace or complexity of academic debates, but to present the faith according to a logical and intelligible order. This same concern for clarity should guide today’s reader as well: the Summa does not seek to obscure truth through complicated language, but rather to explain it in a transparent and accessible way.

How Is the Summa Theologica Structured?

To read the Summa Theologica properly, it is essential to understand its basic unit: the article. This work is not meant to be read like a modern book with continuous prose, but as a series of responses to specific problems, following the medieval method of disputatio. Each article is carefully constructed and follows a fixed structure, designed to treat a question fully and in an orderly manner.

1. Question (Utrum): Introduces the topic in the form of a clear question—whether something is or is not the case. It precisely defines the problem to be examined.
2. Objections (Videtur quod): Presents the strongest arguments against the position that St Thomas Aquinas will ultimately defend. This section invites the reader to reflect and to exercise critical thinking.
3. Sed contra: Appeals to a recognized authority—such as Sacred Scripture, a Church Father, or an ancient philosopher—that supports the truth. It situates the response within the living tradition of the Church.
4. Answer (Respondeo): This is the heart of the article. Here Saint Thomas Aquinas sets forth his principal teaching, grounding it in both reason and faith.
5. Replies to the Objections (Ad): Each objection raised at the beginning is answered individually. This section clarifies doubts and corrects possible misunderstandings.

This method ensures that no difficulty is left unaddressed. For beginners especially, it is crucial to distinguish these parts and to remember that the authentic teaching of St. Thomas Aquinas is found in the Respondeo and in the final replies, not in the initial objections.

What Should I Know Before Starting to Read the Summa Theologica?

Before entering into the theological treatises, it is important for the reader to be familiar with certain basic philosophical concepts that underpin the entire Summa Theologica. Saint Thomas Aquinas draws upon the philosophy of Aristotle and adapts it to place it at the service of the faith. These distinctions are not merely academic details; they are necessary tools for properly understanding what the Angelic Doctor teaches.

Act and potency

For Saint Thomas Aquinas, reality is understood through the distinction between act and potency Act is what a thing actually is here and now; potency is its capacity to become something more. Every change occurs when something passes from potency to act through the action of another being that is already in act.

This principle lies at the foundation of the First Way for demonstrating the existence of God: if everything that is moved must be moved by another, there must exist a First Mover who is Himself unmoved, who does not change, and who is Pure Act. This First Mover is God, in whom there is no potency or change, but the fullness of being.

Essence and existence

Another central teaching of the Summa Theologica is the distinction between essence and existence. Essence answers what a thing is, while existence is that by which a thing actually is. In created beings, these two are not identical: one can understand what a human being is without that human being necessarily existing.

Only in God do essence and existence fully coincide. God does not have being as something added to Him; He is Being itself (ipsum esse subsistens). This shows that everything created depends entirely on God for its existence.

Substance and accidents

To understand visible reality, Saint Thomas distinguishes between substance and accidents. Substance is what a thing is in itself, while accidents are the properties that can change without the thing ceasing to be what it is, such as color, size, or acquired knowledge.

This distinction explains how a person can undergo change over time while remaining the same individual. In sacramental theology, especially in the case of the Eucharist, this teaching is essential for understanding transubstantiation: the substance of the bread is changed, becoming the Body of the Lord, while the accidents (the appearances of bread) remain.

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How many parts does the Summa Theologica have?

The Summa Theologica is organized around a single, unifying idea: everything comes from God and is ordered to return to Him. This movement unfolds as a path of exit and return (exitus–reditus): creatures proceed from God through creation and are led back to Him through grace and the moral life.

First Part (Prima Pars): God and creation

The Prima Pars is the basis of the entire work. It begins by studying God in Himself, treating His existence through the five ways and His divine attributes, such as goodness and immutability. Then it addresses the mystery of the Most Holy Trinity, explaining the relations among the divine Persons.

After contemplating who God is, Saint Thomas explains how creatures proceed from Him. This includes the doctrine of creation, the angels, and finally the human being. The treatise on man is especially important for beginners, as it explains the nature of the soul, its union with the body, and the human faculties, particularly the intellect and free will.

Second Part (Secunda Pars): Man’s Return to God

This part focuses on moral life and shows how man is ordered back to God. It is divided into two major sections:

• Prima Secundae:

Studies the ultimate end of man, which is happiness or beatitude, and the means to achieve it: human acts, passions, virtues, sin, law, and grace.

• Secunda Secundae:

Applies these principles to concrete life. Analyzes the theological and cardinal virtues, along with the vices that oppose them. For many readers, this is the most practical part, as it relates directly to daily spiritual and moral life.

Third Part (Tertia Pars): Christ and the sacraments

The Tertia Pars presents Jesus Christ as the mediator between God and men. Having shown where man comes from and where he is called to go, this part reveals the concrete path: the Incarnation, the life, Passion, and Resurrection of Christ. It also explains the sacraments as the means by which Christ communicates grace to His Church.

This part was left unfinished due to the death of St. Thomas Aquinas and was later completed by his disciples using material drawn from his earlier writings.

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In What Order Should the Summa Theologica Be Read?

For those who are just beginning, following the original order of the Summa Theologica can be challenging, especially because of the philosophical density of its opening questions. For this reason, a more pedagogical reading path is often recommended:

• First stage: The virtues

  • This corresponds to the Secunda Secundae (II–II, questions 1–170).

  • It is the most practical and spiritually oriented part of the work.

  • It helps apply the teaching of St Thomas Aquinas, St. Thomas Aquinas, and Saint Thomas Aquinas to daily Christian life.

• Second stage: The Human Person

  • It is found in the Prima Pars (I, questions 75–102).

  • It helps the reader understand who the human person is, what the soul is, and how the intellect and the will operate.

• Third stage: God and creation

  • Includes the Prima Pars (I, questions 1–44).

  • It establishes the rational foundations of the faith and clarifies who God is and how He created the world.

• Fourth stage: Christ and the sacraments

  • Corresponds to the Tertia Pars (III, questions 1–90).

  • It brings the study to its fulfillment in the person of Jesus Christ and in the means of grace.

Using Commentaries and Guides to Read the Summa Theologica

For a beginner reader, it is very useful to have works that help to translate the thought of Saint Thomas Aquinas into a more more contemporary language. These guides make the text more accessible without sacrificing its doctrinal richness.

Recommended resources

• A Companion to the Summa – Walter Farrell, O.P.

This classic four-volume work offers a complete paraphrase of the Summa Theologica, transforming scholastic language into clear, readable prose while preserving its depth.

• Catechism of the Summa Theologica – Thomas Pègues, O.P.

Each question is summarized in a question-and-answer format, making it ideal for quickly grasping the essential ideas.

• BAC Editions (Biblioteca de Autores Cristianos)

A standard reference in Spanish, these editions include extensive introductions and explanatory notes that clarify technical terms and sources.

• Guides by Étienne Gilson and Josef Pieper

These authors help readers grasp the spirit of Thomism, offering both historical context and an existential understanding of the work of Saint Thomas Aquinas.

Quotes by Saint Thomas Aquinas on study

Saint Thomas Aquinas was not merely an intellectual, but a saint whose intelligence was set ablaze by love. For him, study was an extension of prayer. His advice to Brother John on how to study remains a golden rule for every beginner:

• Gradual Progress

“Do not try to enter the sea all at once, but by way of the rivers.”

One should begin with what is simpler before approaching the deeper mysteries.

• Silence and Recollection:

“Be slow to speak and reluctant to go to the common room.”

The knowledge of truth requires an inner space of stillness in order to listen to the Holy Spirit, the true Master of theology.

• Constant Prayer:
  The light of the intellect must be asked from the “ineffable Creator.”
• Intellectual Charity:
  What matters is not who speaks the truth, but the truth itself—and it must always be taught with love.

The reading of the Summa Theologica should be accompanied by the very prayer that Saint Thomas Aquinas himself prayed before study, asking God to “dispel the double darkness” of sin and ignorance, and to grant “readiness in learning and keenness in interpretation.” The ultimate goal of this study is not the accumulation of information, but the transformation of the soul, so that by knowing God more deeply, one may love Him more fully.

What difficulties might I face when beginning to read the Summa Theologica?

Those who approach the Summa Theologica for the first time often encounter terms that feel unfamiliar or technical. It is important to keep in mind that, in the thought of St Thomas Aquinas, St. Thomas Aquinas, and Saint Thomas Aquinas, words are used with great precision and a clearly defined meaning.

The language of participation

St Thomas Aquinas employs the notion of participation to explain the relationship between God and creatures. God is Being in the fullest sense, whereas creatures exist only because they receive their being from God. This means that nothing exists by itself; everything depends on God at every moment. This teaching avoids two opposite errors: it neither identifies God with the world nor separates Him from His creation, but instead affirms His intimate and provident presence in all that exists.

The relationship between reason and faith

Another common difficulty is discerning the proper roles of reason and faith. For Saint Thomas Aquinas, theology makes use of reason in the service of faith. Reason can attain certain truths—such as the existence of God—but there are mysteries that can be known only through revelation, such as the Trinity or the Incarnation. The Summa Theologica teaches that faith and reason do not contradict one another, because both originate from the same Truth: God Himself.

Why should I read the Summa Theologica?

The Summa Theologica is not merely a book for study; it is also a school of contemplation and spiritual growth. For beginners, its reading provides a solid foundation amid the confusions of modern thought, since it proposes a clear and coherent order that helps organize not only ideas, but one’s entire life. The enduring relevance of St Thomas Aquinas, affirmed by centuries of teaching within the Church and by his profound synthesis of philosophy and faith, makes this work a reliable gateway to a more mature and well-grounded faith.

This importance was rediscovered with particular force in the nineteenth century, when Pope Leo XIII, confronted with the rise of rationalism and subjectivism, pointed to St. Thomas Aquinas as a sure guide for the Christian intellect. In the encyclical Aeterni Patris, he emphasized that the philosophy of Saint Thomas Aquinas safeguards the dignity of human reason without severing it from divine revelation. In this way, theology was reaffirmed not as a matter of personal opinion, but as a true science that employs reason to penetrate more deeply into the truths of faith.

Throughout its pages, the Summa Theologica teaches the reader how to think in harmony with the Church. It leads the intellect from the knowledge of creation to the contemplation of God Himself. With the help of sound commentators and the humble disposition recommended by St Thomas Aquinas himself, the beginner can undertake this journey with confidence, knowing that he or she is walking a secure path of Christian wisdom—one capable of leading toward sanctification and salvation.

Do you want to grow in virtues by imitating the saints? Take a look at these articles that may help you:

• 6 Things You Didn’t Know About Saint Luke: Multifaceted saint who put all his talents at the service of evangelization.
• 5 Remarkable Stories from the Life of Saint Teresa of Avila: Spiritual teacher who lived with intensity, fought against her own weaknesses (like everyone) and allowed herself to be transformed by the love of God.
• Saint Francis of Assisi: the saint most like Christ: His simple existence, marked by detachment, joy, and love for all creatures, as reflections of God, moves to the imitation of Christ.