thing that is spoken of God in an absolute sense, belongs
to the unity of essence. Therefore it must be said that the divine
persons are distinguished from each other only by the relations. Now
the relations cannot distinguish the persons except forasmuch as they
are opposite relations; which appears from the fact that the Father
has two relations, by one of which He is related to the Son, and by
the other to the Holy Ghost; but these are not opposite relations,
and therefore they do not make two persons, but belong only to the
one person of the Father. If therefore in the Son and the Holy Ghost
there were two relations only, whereby each of them were related to
the Father, these relations would not be opposite to each other, as
neither would be the two relations whereby the Father is related to
them. Hence, as the person of the Father is one, it would follow that
the person of the Son and of the Holy Ghost would be one, having two
relations opposed to the two relations of the Father. But this is
heretical since it destroys the Faith in the Trinity. Therefore the
Son and the Holy Ghost must be related to each other by opposite
relations. Now there cannot be in God any relations opposed to each
other, except relations of origin, as proved above (Q. 28, A. 4). And
opposite relations of origin are to be understood as of a
"principle," and of what is "from the principle." Therefore we must
conclude that it is necessary to say that either the Son is from the
Holy Ghost; which no one says; or that the Holy Ghost is from the
Son, as we confess.

Furthermore, the order of the procession of each one agrees with this
conclusion. For it was said above (Q. 27, AA. 2, 4; Q. 28, A. 4),
that the Son proceeds by the way of the intellect as Word, and the
Holy Ghost by way of the will as Love. Now love must proceed from a
word. For we do not love anything unless we apprehend it by a mental
conception. Hence also in this way it is manifest that the Holy Ghost
proceeds from the Son.

We derive a knowledge of the same truth from the very order of nature
itself. For we nowhere find that several things proceed from one
without order except in those which differ only by their matter; as
for instance one smith produces many knives distinct from each other
materially, with no order to each other; whereas in things in which
there is not only a material distinction we always find that some
order exists in the multitude produced. Hence also in th