Thomas Aquinas (c1225-1274) died before he could complete his ambitious plan for Summa Theologica, described as ‘a systematic compendium' of Roman Catholic theology. Drawing on a wide range of Christian sources - and, controversially, on Greek and Latin philosophers as well as Arabian commentators - he sought to explicate matters of doctrine through a specific scheme of Question, Article, Objection, Answer and Reply.

Before his death, Aquinas completed the first 90 Questions of the Third Part. This left a series of issues unexamined. However, the overall scheme was brought to a conclusion by Fra Rainaldo da Piperno (c1230-c1290), a life-long friend and associate of Aquinas. Fra Rainaldo drew on an earlier work by Aquinas, the Commentary on the Fourth Book of the Sentences of Peter Lombard, to produce the Supplement to the Third Part, in which a further 99 Questions are dealt with. It opens with a continuation of the section on Penance, left unfinished on the death of Aquinas. Other general topics covered are Extreme Unction, Holy Orders, Matrimony and the Resurrection. The Supplement closes with two Appendices largely addressing the subject of Purgatory. The translation is by Father Laurence Shapcote of the Dominican Order. Martyn Swain brings clarity and experience to this final segment of Aquinas' magnum opus.