Aquinas on the origination relations of the Son and Spirit

According to Aquinas’s argument thus far, if the Son and Spirit are distinct, then they must have opposite features. The only kinds of opposite features they can have are the correlative features of ‘being the producer of’ and ‘being the product of’ that arise from instances of origination.

Consequently, if the Son and Spirit are distinct, they must each have one of those features. So if we take this argument seriously, Aquinas is saying that all three persons must be distinguished by the features 'being the producer of' and 'being the product of'. Those are the only options. So each divine person must either be the producer of, or produced by, another person.

This goes for the Son and Spirit too. If they are to be distinguished from each other, one must be the producer, and one must be the product. But which is which? Is the Son the producer, or is it the Spirit?

Aquinas simply says that the Son must be the producer of the Spirit, not the other way around, for nobody says that the Spirit produces the Son. Rather, everybody says that the Spirit is given by and from the Son.

Aquinas may be referring to Anselm here. In De processione 15.2 (Schmitt, 215), Anselm argues that either the Son is produced by the Son, or the Son is produced by the Spirit, and since nobody thinks the Son is produced by the Spirit, then it must be that the Son produces the Spirit. Henry of Harclay, when commenting on this particular argument in Aquinas, thinks Aquinas is just plain quoting Anselm here. And that may be.

But in any case, we have finally reached the end of this first argument for the Filioque in the SCG. Whew.