Thomas has shown the properties of the Father that distinguish Him from the Son and the Holy Spirit; in Chapter 58 we move on to the properties of the latter:
Two properties must pertain to the Son: one whereby He is distinguished from the Father, and this is filiation; another whereby, along with the Father, He is distinguished from the Holy Spirit; and this is their common spiration. But no property is to be assigned whereby the Son is distinguished from the Holy Spirit alone, because as we said above, the Son and the Father are a single principle of the Holy Spirit.
This is essential the same as we saw yesterday, with the replacement of paternity with filiation, “son-ship”.
Similarly, no single property is to be assigned whereby the Holy Spirit and the Son together are distinguished from the Father. For the Father is distinguished from them by one property, namely, innascibility, inasmuch as He does not proceed. However, since the Son and the Holy Spirit proceed, not by one procession, but by several, they are distinguished from the Father by two properties. The Holy Spirit has only one property by which He is distinguished from the Father and the Son, and this is called procession. That there cannot be any property by which the Holy Spirit may be distinguished from the Son alone or from the Father alone, is evident from this whole discussion.
I’m finding the above two sections to be somewhat dizzying. I don’t see how the Son proceeds from the Father by several processions. It looks like one procession to me: the Son is the Father’s word. Similarly, the Holy Spirit proceeds from the Father and the Son together, which again looks like one procession. Or, perhaps, Thomas is saying that the Son proceeds from the Father in one way, and hence is distinguished by one property, filiation, while the Spirit proceeds from the Father and Son in another way, and hence is distinguished by a different property, procession. I think that must be it.
Accordingly five properties in all are attributed to the divine persons: innascibility, paternity, filiation, spiration, and procession.
OK, though I think the name of that last one, procession, indicates mental fatigue on somebody’s part, given that paternity, filiation, and spiration all appear to be kinds of procession, generally speaking.