/summa/FP/FPIII/FP_Q31:
We now consider what belongs to the unity or plurality in God; which gives rise to four points of inquiry:
(1) Concerning the word "Trinity";
(2) Whether we can say that the Son is other than the Father?
(3) Whether an exclusive term, which seems to exclude otherness, can be joined to an essential name in God?
(4) Whether it can be joined to a personal term?