Aquinas, ius gentium, and the Decretists

For his conception of the ius gentium, Aquinas took as his starting point the canon law doctrines of Gratian, who himself had adopted ideas from Isidore of Seville. Aquinas's conception of the ius gentium was different of Gratian's and relied to a large extent on the civilian interpretation of Roman law texts. This article analyzes how the decretists, the first interpreters of Gratian, arrived at a conception of the ius gentium that was different from that of Gratian himself, and thus paved the way for Aquinas to read the Roman law conception into the ius gentium.