Thomas Aquinas
Dominican friar and author of the Summa Theologiae. On the question of how many divine persons there are, he is the sharpest witness against slot-counting: he holds that there are four real relations in God and three persons, and explains the mismatch.
Aquinas matters here less for his conclusions than for a piece of arithmetic he does openly. He holds that there are four real relations in God and three persons, and rather than smoothing this over he explains it: relations distinguish persons only when they are opposed to each other.
He also meets the underlying problem head-on. The objection that every real relation needs two really distinct terms is one he states in almost the words a modern critic would use, and he accepts it, answering that the ordering of a thing to itself under two descriptions is not a real relation at all.
The upshot for anyone reaching for "three roles, therefore three persons" is uncomfortable. That inference is not the tradition's best apparatus. It is something the tradition's best apparatus contradicts.
Where this comes up
Sources
- Thomas Aquinas, Summa Theologiae Ia qq. 28, 30, 36, 39