06.How the Spirit proceeds

4 How the Spirit proceeds from the Father and the Son

We must also observe that every act of knowledge is followed by an act of the appetite. Of all appetitive acts love is the principle. Without it there is no joy at gaining something one does not love, or sadness at missing something one does not love - that is, if love is taken away; likewise all other appetitive acts would go, since they are all somehow related to sadness and joy. Therefore, since God has perfect knowledge, he must also have perfect love, which arises as the expression of an appetitive act, as a word arises as the expression of an intellective act. But there is a difference between an intellectual and an appetitive act. For an intellectual act and any other act of knowledge takes place by the knowable thing somehow existing in the knowing power, namely, sensible things in the sense and intelligible things in the intellect. But an appetitive act takes place by an orientation and movement of the appetitive power to the things exposed to the appetite. Things that have a hidden source of their motion are called spirits. For instance, winds are called spirits because their origin is not apparent. Likewise breath, which is a motion from an intrinsic source, is called spirit. So, as divine things are expressed in human terms, the very love coming from God is called a spirit. But in us love comes from two different sources. Sometimes it comes from a bodily and material principle, which is impure love, since it disturbs the purity of the mind. Sometimes it comes from the a pure spiritual principle, as when we love intelligible goods and what is in accord with reason; this is pure love. God cannot have a material love. Therefore we fittingly call his love not simply Spirit, but the Holy Spirit, since holiness refers to his purity.

It is clear that we cannot love anything with an intelligible and holy love unless we conceive it through an act of the intellect. The conception of the intellect is a word; so love must arise from a word. We call the Word of God the Son; so it is clear that the Holy Spirit comes from the Son. Just as God’s act of knowledge is his very being, so also is his act of loving. And just as God is always actually understanding, so also he is always actually loving himself and everything else by loving his own goodness. Therefore, as the Son of God, who is the Word of God, subsists in the divine nature and is co-eternal with the Father and perfect and unique, likewise we must profess the same about the Holy Spirit.

Since everything that subsists with an intelligent nature we call a "person", which is equivalent to the Greek "hypostasis", it is necessary to say that the Word of God, whom we call Son, is a hypostasis or person. No one doubts that God, from whom a word and a love comes forth, is a subsistent reality, and can also be called a hypostasis or a person. Thus we fittingly posit three persons in God: the person of the Father, the person of the Son and the person of the Holy Spirit.

We do not say that these three persons or hypostases are distinct by essence, since, just as God’s act of knowing and loving is his very being, so also his Word and Love are the very essence of God. Whatever is absolutely asserted of God is nothing other than his essence, since God is not great or powerful or good accidentally, but by his essence. So we do not say the three persons or hypostases are distinct absolutely, but by mere relations which arise from the coming forth of the word and the love.

Since we call the coming forth of the word generation, and from generation result the relationships of fatherhood and sonship, we say that the person of the Son is distinct from the person of the Father only by fatherhood and sonship, while all else belongs to both commonly and without distinction. Just as we call the Father true God, almighty, eternal and whatever else, so also the Son, and for the same reason the Holy Spirit.

Therefore, since the Father and the Son and the Holy Spirit are not distinct in their divine nature, but only by relationship, we are right in saying that the three persons are not three gods, but one true and perfect God.

Three human persons are three men and not one man, because the nature of humanity, which is common to them, belongs to each separately because they are materially distinct, which does not apply to God. So in three men there are three numerically different human natures, while only the essence of humanity is common to them. But in the divine persons there are not three numerically different divine natures, but necessarily only one simple divine nature, since the essence of God’s word and of his love is not different from the essence of God. So we profess not three gods, but one God, because of the one simple divine nature in three persons.