The “Summa Theologica” of St. Thomas Aquinas. Part I. Literally translated by Fathers of the English Dominican Province. Second and revised edition (London: Burns Oates and Washbourne, 1920-1922). 10 vols. http://oll.libertyfund.org/titles/1978,
A multi-volume collection of Aquinas’ greatest work on philosophy and theology.
The text is in the public domain.