On The Holy Trinity by St. Augustine
Chapter 1.--It is Shown by Reason that in God Three are Not Anything Greater Than One Person.
2. For we say that in this Trinity two or three persons are not anything greater than one of them; which carnal perception does not receive, for no other reason except because it perceives as it can the true things which are created, but cannot discern the truth itself by which they are created; for if it could, then the very corporeal light would in no way be more clear than this which we have said. For in respect to the substance of truth, since it alone truly is, nothing is greater, unless because it more truly is. But in respect to whatsoever is intelligible and unchangeable, no one thing is more truly than another, since all alike are unchangeably eternal; and that which therein is called great, is not great from any other source than from that by which it truly is. Wherefore, where magnitude itself is truth, whatsoever has more of magnitude must needs have more of truth; whatsoever therefore has not more of truth, has not also more of magnitude. Further, whatsoever has more of truth is certainly more true, just as that is greater which has more of magnitude; therefore in respect to the substance of truth that is more great which is more true. But the Father and the Son together are not more truly than the Father singly, or the Son singly. Both together, therefore, are not anything greater than each of them singly. And since also the Holy Spirit equally is truly, the Father and Son together are not anything greater than He, since neither are they more truly. The Father also and the Holy Spirit together, since they do not surpass the Son in truth (for they are not more truly), do not surpass Him either in magnitude. And so the Son and the Holy Spirit together are just as great as the Father alone, since they are as truly. So also the Trinity itself is as great as each several person therein. For where truth itself is magnitude, that is not more great which is not more true: since in regard to the essence of truth, to be true is the same as to be, and to be is the same as to be great; therefore to be great is the same as to be true. And in regard to it, therefore, what is equally true must needs also be equally great.