Summa Theologica

Aquinas began this enormous work around 1265 as a teaching manual, meant to spare beginning students the disorder of the textbooks then in use. The Prima Pars, its first part, takes up God: whether his existence can be demonstrated (the famous five ways open it), what may be said of his nature, then creation, the angels, and the making of human beings. Every topic arrives as a question, with the objections stated first and answered last, so the reader watches an argument being built rather than handed down. Aristotle, Augustine, Avicenna, and Maimonides are all put to work. He never finished it; after something he experienced at Mass in 1273, he called all he had written straw. Free PDF and EPUB editions are available for download.