THE SCHOOLMEN body and blood of Christ The hymns which St Thomas wrote for the oYce remain popular among Catholics, and the sequence of the Mass, Lauda Sion, renders the doctrine of transubstantiation into surprisingly lively and singable verse The most important achievement of this middle period of St Thomas’ life was the Summa contra Gentiles, begun just before the departure from Paris, and completed at Orvieto in 1265 Its title, literally translated, means ‘Summary, or Synopsis, against Unbelievers’; its most frequently used English translation bears the title On the Truth of the Catholic Faith According to a fourteenth-century tradition, now often discounted by scholars, the book was a missionary manual, written at the request of the Spanish Dominican Raymond of Penafort, who was evangelizing non-Christians in Spain and North Africa Whatever the truth of this story, the book diVers from St Thomas’ other major treatises in taking its initial stand (throughout the Wrst three of its four books) not on Christian doctrine, but on philosophical premisses that could be accepted by Jewish and Muslim thinkers versed in Aristotelian philosophy Thomas explains his method thus: Muslims and pagans not agree with us in accepting the authority of any Scripture we might use in refuting them, in the way in which we can dispute against Jews by appeal to the Old Testament and against heretics by appeal to the New These people accept neither Hence we must have recourse to natural reason, to which all men are forced to assent (ScG 2) Thus, the text is not a work of revealed theology, but of natural theology, which is a branch of philosophy The Summa contra Gentiles is a treatise, not a record of disputations; it is in four books of a hundred or so chapters each, amounting in total to some 300,000 words The Wrst book is about the nature of God, in so far as this is held to be knowable by reason unaided by revelation The second concerns the created world and its production by God The third expounds the way in which rational creatures are to Wnd their happiness in God, and thus ranges widely over ethical matters The fourth is devoted to speciWcally Christian doctrines such as the Trinity, the Incarnation, the sacraments, and the Wnal resurrection of the saints through the power of Christ In the Wrst three books Aquinas is scrupulous to use biblical or ecclesiastical texts only as illustrations, never as premisses from which the arguments start 67