Summa contra Gentiles

The Summa contra Gentiles (also known as Liber de veritate catholicae fidei contra errores infidelium, "Book on the truth of the Catholic faith against the errors of the unbelievers") is one of the best-known treatises by St Thomas Aquinas, written as four books between 1259 and 1265.

It was probably written to aid missionaries in explaining the Christian religion to and defending it against dissenting points of doctrine in Islam and Judaism. To this end, Aquinas could rely on a substantial body of shared doctrine, especially tenets of monotheism, in the case of Judaism the shared acceptance of the Old Testament as scripture and in the case of Islam the (at the time) shared tradition of Aristotelian philosophy.[1]

Whereas the Summa Theologiæ was written to explain the Christian faith to theology students, the Summa contra Gentiles is more apologetic in tone, as it was written to explain and defend the Christian doctrine against unbelievers, with arguments adapted to fit the intended circumstances of its use, each article refuting a certain heretical belief or proposition. Instead of a mere elucidation of the length and breadth of Christian doctrine, Aquinas explains specific core articles of Christian belief.[1]


The conventional title Summa contra Gentiles, found in some of the earliest manuscripts, is sometimes given in the variant Summa contra Gentes.[2] The title is taken from chapter I.2, where Thomas states his intention as the work's author:

I have set myself the task of making known, as far as my limited powers will allow, the truth that the Catholic faith professes, and of setting aside the errors that are opposed to it. To use the words of Hilary: 'I am aware that I owe this to God as the chief duty of my life, that my every word and sense may speak of Him' (De Trinitate I, 37).[3]

A longer title is also given as Tractatus de fide catholica, contra Gentiles (or: contra errores infidelium), meaning "Tractate on the universal faith, against the pagans" (or, against the errors of the unbelievers). This is often shortened to De fide Catolica.