This work demonstrates the extent to which St Thomas Aquinas studied and used canon law in his theological and philosophical work. Not only did Aquinas quote texts of canon law in passages where he deals with directly juridical and canonical questions, but he also borrows from legislative texts and the works of canonists’ arguments that are used in his theological demonstrations.

The book compiles several specific studies that demonstrate his extensive knowledge of the law and the place that Aquinas attributes to it. The idea of St Thomas Aquinas as an important author in the field of law, was commonly accepted in the Thomistic sphere and among the canonists belonging to this school. It was commonly held that the positions of St Thomas had served to ensure the orientations of canon law, particularly about the legislation of the sacraments or the reflection on the notions of law or right. However, the present study provides many precise and convincing elements that go far beyond that. The results of these studies will now have to be taken for granted. It should be noted in the first place that St Thomas had a good knowledge of the work of Gratian, of the collections of Roman law and the Decretals, and also of the works of the canonists, notably Raymond de Peñafort. It is also established that the author of Summa Theologica attributed to them a place and a role of authority in theology. Obviously, this fact does not constitute St Thomas as a perfect specialist of the whole of juridical and canonical literature, nor a fortiori a Decretist or a Decretalist, but rather as an author to be known as important for medieval law.

The first study proposed by Atria Larson profoundly renews the knowledge of the relationship between Raymond de Peñafort and St Thomas Aquinas (pp 3–29). In particular, Larson manifests the place of the canonist’s works in the Dominican studies that Aquinas followed in his early years and of their use in his later works. Among the studies that establish how the theologian uses law in theology, two major areas must be mentioned, one rather expected, that of moral theology, the other the theology of the sacraments. In the moral part, we can begin by mentioning Andrew Hofer’s study on the quarrel between mendicants and seculars. St Thomas relies on canon law, and in particular on Gratian’s Decretum, to support his defence of these religious of a new type, the Dominicans and the Franciscans (pp 31–54, appendix with synoptic table, pp 54–68).

Justin Anderson’s study presents an original vision of the relationship between theology and canon law based on the study of scandal and truth, more specifically when scandal is considered a sin (pp 94–122). St Thomas reasoned from the key concept of the triplex veritas dating back to Petrus Cantor and widely exploited by the medieval canonical tradition. Anderson shows how St Thomas appropriates this concept while giving it a new scope, applying to it, in particular, the definition of truth as adequatio ad rem and its rational and doctrinal dimension (pp 109–113).

Ken Pennington is interested in the more classical question, among commentators, of the distinction and relationship between lex and ius (pp 123–141). Pennington studies these relations, in particular, from the understanding of the distinction between lex naturalis and ius naturale. In this respect, somewhat contrary to other studies, Pennington holds that Aquinas is ‘only imperfectly’ aware of medieval jurisprudence’ (p 129). This study is complemented by that of Andrea Padovani: ‘Thomas Aquinas’s terminology of ius and lex’ (pp 144–156). Padovani emphasises that the patrimony exploited by St Thomas comes first from Augustine and then from Isidore of Seville, who transmitted to him the Roman notions of law and right. These two notions are also specified by the distinctions of origin, namely natural or divine, and of human or divine character. These notions seen, through the virtue of justice or that of the law, lead to different presentations of legal reality.

In the field of moral theology, Burt Wauters’s very pertinent study on property and redistribution (pp 157–183) should be noted. Here, St Thomas speaks of the origin of private property (pp 164–169). St Thomas does not hesitate to rely on studies of canonicals such as those of Huguccio, Raymond and John the Teutonic (pp 165–166). When addressing this question, St Thomas resorts to the distinction between ius gentium and ius civile. Wauters delivers a very clear conclusion that could be useful to many of the fields studied: ‘There is no doubt that canonistic thinking informed the property theory of Aquinas’ (p 177).

In the field of sacramental theology, we can note Thierry Sol’s study on the Thomistic apprehension of simony in which Sol shows how canonical determinations are taken up and studied by St Thomas (pp 231–254). Charles Reid delivers a remarkable study of the approach to the sacrament of marriage in St Thomas’s theological ensemble and shows how this understanding is based on a good knowledge of canon law (pp 300–333).

Finally, we must mention in an even more special way Reginald Lynch’s study of St Thomas’s recourse to the work of Gratian in his theology of the Eucharist (pp 255–267, with an ample synoptic table given in the appendix, pp 267–279). The study on natural law and baptism in St Thomas allows us to account for the use of the notion of the power of parents over a child (IIIa q 68 a 10 on the baptisms of Jewish children). This right may be enforceable against the need to subject all children to it (pp 280–298). Here, one could envisage a conflict between the revelation carried by ecclesial law and natural law. However, canon law, enunciated in particular in the law of the conciliar canons and the Decretals, as St Thomas receives it, prevents forced baptism against the will of the parents (p 293). St Thomas also proves that forced baptism is against the natural law, because it is against reason (pp 295–296).

After reading this remarkable book, two conclusions emerge. On the one hand, when St Thomas Aquinas was preparing the writing of these works, he had recourse to ‘dossiers’ in which legal and canonical texts feature prominently. The authors emphasise that we can find elements such as: Roman law or pontifical law, or the teachings of canonists and first and foremost the Decretum of Gratian, in its ‘theological’ but also ‘juridical’ parts, and the other medieval jurisconsults and probably also his Dominican colleague Raymond de Peñafort. On the other hand, and more profoundly, St Thomas knows canon law and its great principles. He does not hesitate to use his concepts, to confront his theories, to take them into account and sometimes without neglecting to challenge them. He can also have recourse to it in his theology, particularly moral and sacramental. It will now be necessary to take into account this new quality recognised in St Thomas Aquinas.