Born in Italy in 1225, and despite a relatively short career that ended around 50 years later in 1274, Thomas Aquinas went on to become one of the most influential medieval thinkers on political and legal questions. Aquinas was educated at both Cologne and Paris, later taking up (after some controversy) a chair as regent master in theology at the University of Paris, where he taught during two separate periods (1256-1259, 1269-1272). In the intermediate period he helped establish a studium for his Order in Rome, beginning work on the Summa Theologiae, the masterwork for which he is still well-known. Subsequent to an experience (traditionally, a vision) Aquinas had on the feast of St. Nicholas in 1273, Aquinas intentionally refrained from further work on that text, so that it remained incomplete at the time of his death a year later in 1274. Apart from his own contributions, the Thomistic school – including followers within and without the Dominican Order to which Aquinas belonged – has had profound and far-reaching influence upon the history of legal thought in the West. Many of the classical developments of Thomistic thought are written as commentaries on the Summa Theologiae (hereafter, ST), including the works of Tomasso de Vio (Cajetan) and those of Domingo Banez, Francisco de Vitoria, Bartholome de las Casas, and the other highly influential members of the School of Salamanca who are noteworthy for developing Aquinas’ political and legal thought in the 16th century.
Specifically, the ways in which Aquinas synthesized classical political and legal themes around the law, morality, and the common good provided a touchstone for what has come to be called ‘natural law jurisprudence.’ Natural law thinkers, in short, appeal to objective facts about what is good for human beings, and the social or political nature of the kind of creatures that we are, as a standard against which we measure the legal and social institutions created by human institutions. What is crucial here is that facts about human beings as social animals constitute reasons for individuals and groups to act or be structured in certain ways, such that ‘nature’ is the proper source for jurisprudential and political principles.