B. What the Idea is of the Being in of the Divine Persons

58. As to the second article [n.37] I say that the reason for this being in is neither the essence nor the relation alone [n.42].

59. My proof of the first point [n.58] is that then the Father would be in himself, which is false in the way in which the Savior understands the Father to be in the Son and the Son in the Father [n.36], because this way of being in requires a real distinction.

60. My proof of the second point [n.58] is:

First that the relations of origin do not have the same idea in the related persons, and so if these were the formal reasons for the being ‘in’ of the persons in each other the persons would not be in each other uniformly, - which is contrary to what was before said [nn.54, 57].

Second that if per impossibile this God were to produce another God, this God would not be in that God, because - according to John Damascene On the Orthodox Faith ch.5 - if there were two Gods they could not be together at the same time, and so neither would be immense, and so neither would be God; and yet there would be a true relation of the producer to the produced.

Next, third, that if per impossibile there were two persons without origin, but if they had the same essence along with a real distinction, they would be in each other, because the essence of one person could not be in the other if the relation itself (which is altogether the same as the essence) were not in it, although in another way of being ‘in’, because what the foundation is in the relation is also in, even though one person would not be from the other in origin; therefore the relative property is not ‘in’ the cause.

Then, fourth, that in creatures there are truly relations of origin, of the thing that is a principle and of the thing that has a principle, and yet there - because of the diversity of nature in the things related - neither is in the other.

61. And from these arguments it follows that, since there is in the persons only essence and relation, according to the common opinion [e.g. of Henry of Ghent and Thomas Aquinas], therefore both of them will be the total reason for the being in [n.42].

62. And to understand how this is so, one can take an example about likeness in creatures: for according to Hilary ([On the Trinity III n.23] and it is set down in Lombard, Sent. d.31 ch.1 n.266), nothing is like itself but like another; yet likeness is founded on unity in quality, according to the Philosopher Metaphysics 5.15.1021a11-12, the chapter ‘On Relation’; so neither the mere diversity of the related things, nor the mere unity of the foundation, suffices for likeness, but both are required per se as one total cause. - So it is here: neither the distinction between the person who is in another and the person in whom the other is, nor the unity of the essence by which they are in each other, is the whole reason for the being in, but both together are. Yet just as unity of foundation in the case of likeness is the more principal, and likewise the more immediate, reason than the distinction between the related things, so here unity of essence can be posited to be the more immediate and more principal reason for this being in than the distinction of the persons.