/summa/FP/FPIII/FP_Q40:
We now consider the persons in connection with the relations, or properties; and there are four points of inquiry:
(1) Whether relation is the same as person?
(2) Whether the relations distinguish and constitute the persons?
(3) Whether mental abstraction of the relations from the persons leaves the hypostases distinct?
(4) Whether the relations, according to our mode of understanding, presuppose the acts of the persons, or contrariwise?