Summa summae S. Thomae sive compendium theologiae

Note. Generation, insofar as it applies even to non-living things, is a change from non-being to being in some subject. But insofar as it belongs only to living things, it is commonly defined as: “The origin of a living being from a living being in the likeness of a specific nature.”

It is said in the likeness of a nature because that which is generated must not only be similar to the generator in itself and essentially, but must also proceed as similar to the generator by the power and mode of the procession itself. That is, the mode of procession, considered according to its species and not merely according to the individual, must be a mode of assimilation, or must contain within itself the reason why what proceeds is similar to its principle. Thus the proposition “A generator assimilates” is as formally true in the fourth mode of per se predication, as philosophers speak, as the following propositions: “A builder builds; what is hot heats; a musician sings.” The reason is: first, because definitions are understood in their formal sense; secondly, because the whole formality of generation consists in the expression of likeness, or in the propagation of a nature as similar; nor is generation anything other than the expression of a likeness that propagates itself, according to the text of Genesis v, 3: Adam begot a son in his own image and likeness. In the absence of this condition, Eve, formed from Adam's rib, was not generated, nor was she his daughter. For although she is essentially human, like Adam, and although by virtue of that procession, considered according to the individual, she proceeded similar to him, nevertheless she did not proceed similar by virtue of the procession considered according to its species. For the mode of proceeding from a rib is not assimilative, nor does it contain the reason why what is thus produced should be similar in nature to that from whose rib it is produced. Indeed, a horse or anything else whatsoever could have been made from that rib. Not so in the case of the generative action established by nature.

Therefore, among the various opinions, the more probable is the following:

I answer: The procession of the Word is generation, whereas the procession of the Holy Spirit is not, because the procession of the Word is through the intellect, whose power is assimilative, whereas the procession of the Holy Spirit is through the will, whose power is not assimilative.¹

Sacred Scripture favors this position. For when it calls the Word the Son, and does not call that which is not the Word the Son, it indicates that He is Son because He is the Word, and that the Spirit is not Son because He is not the Word. Accordingly, St. Augustine says in Book VII of On the Trinity, chapter 2, no. 3: “He is Son insofar as He is Word, and He is Word insofar as He is Son.” Likewise Athanasius in Orations 2 and 3 against the Arians; Ambrose in On the Incarnation, chapter 3; and others.

The proof is by reason. It belongs to the nature of generation that what proceeds should proceed into the likeness of a nature by its own power and of itself, that is, when considered according to its species. But this belongs to the procession which is through the intellect, and not to the procession which is through the will. Therefore. The major premise is evident from what was said at the beginning of the article. The minor is proved as follows. This is the difference between intellect and will: the intellect understands because the thing understood is present in the intellect according to its likeness. Therefore, considered according to its species, it is by its own power and of itself assimilative. The will, however, wills not because some likeness of the thing willed is present in the will, but because the will has a certain inclination toward the thing willed. Therefore, the procession that is according to the intellect is by its own power and of itself according to the notion of likeness; but the procession that is according to the will is not by its own power and of itself according to the notion of likeness, but rather according to the notion of something impelling and moving toward an object.

[Note. The processions distinguish the persons only really, but do not separate them. For, being consubstantial, they adhere indivisibly to one another in one and the same numerical essence and substance. Hence follows what theologians call circuminsession, which in divine matters is defined as: “The mutual existence or indwelling of the divine persons in one another,” so that the Father is in the Son, the Son in the Father, the Father and the Son in the Holy Spirit, and the Holy Spirit in both. Thus Christ, speaking of Himself in relation to the Father, says in John XIV, 10 and 11: The Father abiding in me, He does the works. Do you not believe that I am in the Father, and the Father in me? Concerning the Holy Spirit it is said in the same Gospel, XV, 26, that He proceeds from the Father. Yet the Holy Spirit, just like the Son, does not proceed from the Father in such a way as to depart from Him, because the processions, being necessary, are substantial and immanent.

Nor does the statement of the Son in John XVI, 28 create any difficulty: I came forth from the Father; for this either expresses His eternal and immanent procession by generation, whereby He comes forth as a person while remaining in the bosom of the Father by reason of the common nature; or, more particularly, it signifies His visible mission through the Incarnation, as is indicated by the words that follow: And I came into the world.]