Chapter 49 — That the Holy Spirit proceeds from the Father and the Son

We should recall that the act of understanding proceeds from the intellectual power of the intellect. Now the object known is present in the one knowing according as the intellect understands in act. Therefore, the presence of the object known in the knower proceeds from the intellectual power of the one knowing, and this is its word, as we said above. Likewise, what is loved is in the lover when it is actually loved. And the fact that an object is actually loved proceeds from the lover’s power to love and from the lovable good as actually understood. Therefore, the presence of the beloved in the lover proceeds from two things: the loving principle and the intelligible object as apprehended, which is the word conceived about the lovable object. Therefore, since in God knowing and loving himself the Word is the Son, and the one whose Word he is, is the Father of the Word, as is clear from the things said, it is necessary that the Holy Spirit, who pertains to the love whereby God is in himself as beloved in lover, proceeds from the Father and the Son. And so we say in the Creed: who proceeds from the Father and the Son.

Properties of the Trinity