Summa Theologiae Secunda Secundae, 1-91 (Latin-English Opera Omnia) (Latin and English Edition) by Saint Thomas Aquinas

The most important work of the towering intellectual of the Middle Ages, Thomas Aquinas's Summa Theologiae remains one of the great seminal works of philosophy and theology, while extending to subjects as diverse as law and government, sacraments and liturgy, and psychology and ethics. One of the largest volumes in the Summa Theologiae, Thomas tackles every virtue and every vice, laying out their relations, causes, and definitions.