1 Objection 1: It would seem that the Son and the Father are not in each other. For the Philosopher Phys. iv, text. 23) gives eight modes of one thing existing in another, according to none of which is the Son in the Father, or conversely; as is patent to anyone who examines each mode. Therefore the Son and the Father are not in each other.
1 Ad quintum sic proceditur. Videtur quod filius non sit in patre, et e converso. Philosophus enim, in IV Physic., ponit octo modos essendi aliquid in aliquo; et secundum nullum horum filius est in patre, aut e converso, ut patet discurrenti per singulos modos. Ergo filius non est in patre, nec e converso.
2 Objection 2: Further, nothing that has come out from another is within. But the Son from eternity came out from the Father, according to Micheas 5, 2: His going forth is from the beginning, from the days of eternity. Therefore the Son is not in the Father.
2 Praeterea, nihil quod exivit ab aliquo, est in eo. Sed filius ab aeterno exivit a patre, secundum illud Micheae V, egressus eius ab initio, a diebus aeternitatis. Ergo filius non est in patre.
3 Objection 3: Further, one of two opposites cannot be in the other. But the Son and the Father are relatively opposed. Therefore one cannot be in the other.
3 Praeterea, unum oppositorum non est in altero. Sed filius et pater opponuntur relative. Ergo unus non potest esse in alio.
4 On the contrary, It is said Jn. 14, 10): I am in the Father, and the Father is in Me.
4 Sed contra est quod dicitur Ioan. XIV, ego in patre, et pater in me est.
5 I answer that, There are three points of consideration as regards the Father and the Son; the essence, the relation and the origin; and according to each the Son and the Father are in each other. The Father is in the Son by His essence, forasmuch as the Father is His own essence and communicates His essence to the Son not by any change on His part. Hence it follows that as the Father's essence is in the Son, the Father Himself is in the Son; likewise, since the Son is His own essence, it follows that He Himself is in the Father in Whom is His essence. This is expressed by Hilary De Trin. v), The unchangeable God, so to speak, follows His own nature in begetting an unchangeable subsisting God. So we understand the nature of God to subsist in Him, for He is God in God. It is also manifest that as regards the relations, each of two relative opposites is in the concept of the other. Regarding origin also, it is clear that the procession of the intelligible word is not outside the intellect, inasmuch as it remains in the utterer of the word. What also is uttered by the word is therein contained. And the same applies to the Holy Ghost.
5 Respondeo dicendum quod in patre et filio tria est considerare, scilicet essentiam, relationem et originem; et secundum quodlibet istorum filius est in patre, et e converso. Secundum essentiam enim pater est in filio, quia pater est sua essentia, et communicat suam essentiam filio, non per aliquam suam transmutationem, unde sequitur quod, cum essentia patris sit in filio, quod in filio sit pater. Et similiter, cum filius sit sua essentia, sequitur quod sit in patre, in quo est eius essentia. Et hoc est quod Hilarius dicit, V de Trin., naturam suam, ut ita dicam, sequitur immutabilis Deus, immutabilem gignens Deum. Subsistentem ergo in eo Dei naturam intelligimus, cum in Deo Deus insit. Secundum etiam relationes, manifestum est quod unum oppositorum relative est in altero secundum intellectum. Secundum originem etiam manifestum est quod processio verbi intelligibilis non est ad extra, sed manet in dicente. Id etiam quod verbo dicitur, in verbo continetur. Et eadem ratio est de spiritu sancto.
6 Reply to Objection 1: What is contained in creatures does not sufficiently represent what exists in God; so according to none of the modes enumerated by the Philosopher, are the Son and the Father in each other. The mode the most nearly approaching to the reality is to be found in that whereby something exists in its originating principle, except that the unity of essence between the principle and that which proceeds therefrom is wanting in things created.
6 Ad primum ergo dicendum quod ea quae in creaturis sunt, non sufficienter repraesentant ea quae Dei sunt. Et ideo secundum nullum eorum modorum quos philosophus enumerat, filius est in patre, aut e converso. Accedit tamen magis ad hoc modus ille, secundum quem aliquid dicitur esse in principio originante, nisi quod deest unitas essentiae, in rebus creatis, inter principium et id quod est a principio.
7 Reply to Objection 2: The Son's going forth from the Father is by mode of the interior procession whereby the word emerges from the heart and remains therein. Hence this going forth in God is only by the distinction of the relations, not by any kind of essential separation.
7 Ad secundum dicendum quod exitus filii a patre est secundum modum processionis interioris, prout verbum exit a corde, et manet in eo. Unde exitus iste in divinis est secundum solam distinctionem relationum, non secundum essentialem aliquam distantiam.
8 Reply to Objection 3: The Father and the Son are relatively opposed, but not essentially; while, as above explained, one relative opposite is in the other.
8 Ad tertium dicendum quod pater et filius opponuntur secundum relationes, non autem secundum essentiam. Et tamen oppositorum relative unum est in altero, ut dictum est.