 What Peter Lombard’s Sentences are to the sentences genre, Thomas Aquinas’s two great summae, the Summa Contra Gentiles and Summa Theologiae are to the summa form. As with sentences collections, there are two aspects of the form to be considered: the overall organizing structure and the method of confronting individual problems or questions. In terms of overall structure, the Contra Gentiles is a reflection of Aquinas’s distinction between those things which can be known by reason alone (e.g., that God exists) and those things which cannot be arrived at without revelation (e.g., the Trinity and Incarnation). Hence, the first three books of the Summa Contra Gentiles, dealing with God and creation, use arguments which depend only on reason to reach and support its conclusions. The fourth book is concerned with those things that are known only through revelation, in which revelation offers the principles from which the conclusions are drawn. The form for handling individual issues and problems in the Contra Gentiles is not the quaestio but a more affirmative defense of specific positions and against specific heresies. And though it is unclear whether the title summa is original (Jordan 1986, 182–3), the work fits the summa form in its systematic arrangement of topics and its attempt to include all possible arguments for a given position and against its contrary. It has been argued that the Contra Gentiles is not a polemical but a protreptic work, addressed to Christians, calling on them to deepen their understanding of the faith, specifically about how to persuade others to Christian belief (Jordan 1986, 190, 194). On this view the gentiles in the title are not Muslims and Jews but the “pre- or extra-Christian man, and metaphorically, the human mind under the tutelage of nature” (Jordan 1986, 184).