My friend from graduate school days, Fr. Kevin Flannery, S.J., of the Gregorian University in Rome, visited the campus last week and led a seminar on the above topic, examining the rationale underlying the famous distinction between “formal” and “material” cooperation, the locus classicus of which is the following text from St. Alphonsus Liguori.

Sed melius cum aliis dicendum, illam esse formalem quae concurrit ad malam voluntatem alterius, et nequit esse sine peccato; materialem vero illam, quae concurrit tantum ad malam actionem alterius, praeter intentionem cooperantis

[Alphonsus Maria de Ligorio, Theologia moralis, ed. L. Gaudé (Rome: Typographia Vaticana, 1905–1912 (4 vv.)), 2, §63 (v.1 p.357)].

My main question centered on the precise meaning of “concurrit ad” in the passage: if it does not mean the same as “cooperate with,” in which case the definition would be circular, then what does it add, and why was it chosen for this delicate point?  I had my own idea, and I asked Fr. Flannery about his understanding of it.

I’ve since answered the question to my own satisfaction, at least, by doing a search of all uses of the phrase in St. Thomas and discovering that it means, in that corpus, “serves as a contributing cause of,” — which I believe is the sense in which Liguori uses it as well.