Thomas Aquinas’ Summa Theologica (Synopsis of Theology) is a vision of how the world came into existence and what it is for. Published in 1485, over 200 years after its author’s death, the book is widely considered a masterpiece of Western literature.

Key context: In the early Middle Ages, theology essentially was philosophy. It grappled with all questions of meaning, knowledge and even human behaviour – long before the discipline of psychology was invented.

Aquinas intended the Summa as the ultimate beginner’s guide to Christian theology. He feared that existing explanations of the ‘sacred science’ could be confusing, so he set out to answer every conceivable question or argument with clarity and a never-before-seen rigor.

Aquinas felt that any smart Christian should be able to defend their faith in a rational way. That inspired him to create a manual for dealing with religious doubt. It’s one reason why the Summa follows a classical pattern: an argument is presented, then demolished conclusively.

The Summa grew into a multi-volume work that took a decade to write. After experiencing a mystical vision, Aquinas couldn’t bring himself to finish it and died soon after, in 1274. But before we jump into the book’s significance, let’s take a look at the author’s remarkable life.

Aquinas was born around 1224 into an aristocratic Napolitan family. When he decided to join the Dominicans (then a newish order) instead of the established Benedictines, his family were infuriated. They kept him imprisoned for a year and tried to have him seduced by a sex worker.

Aquinas escaped and became a student of Albertus Magnus in Cologne. He ended up becoming a professor of theology in Paris but left that position to write Summa Contra Gentiles, his first Christianity ‘explainer’, before establishing a new Dominican college in Rome.

It was in Rome that he began writing the Summa: a brilliant synthesis of Aristotelian philosophy and Christian theology. But Aquinas also drew on Islamic and Jewish thinkers as well as ancient pagan scholars, which led to criticism from the Church.

You might be wondering, “What’s so unusual about that?” Well, what made Aquinas special is that he was more open-minded than even many of today’s Christians. He accepted that truth was truth, wherever one found it.

Part One of the Summa covers the nature of God, souls, and divine governance. Part Two lays out Aquinas’ philosophy of ethics. Part Three looks at the sacraments, the incarnation and the Trinity. For simplicity’s sake, this Memo will focus on his most enduring work: Part One.