Kathleen Fitzpatrick’s contribution to Trinity and Salvation is on the Trinity and music. Fitzgerald overstates when she called about “musical refutation” of heresy, but her analogies are illuminating.
She points to chords as vestigiae Trinitatis: “Each note of the major triad has its own specific relationship with the other notes: The first and second note of the chord form a major third; the first and third note form a perfect fifth; the second and third note form a minor third. If the relationship between any of these notes is changed, the chord loses its identity; in effect it cannot be itself if any of the notes change the way they relate to each other as major or minor third or perfect fifth.” She suggests that in the same way “the persons of the Trinity . . . give all to each other in a spirit of reciprocity except their characteristic identifying way in which they relate to each other” (154).
That last is awkward; Fitzgerald’s point is that the Persons are in mutual relation, but the particular shape of that relation differences - the Father has a paternal relationship to the Son that is not replicated in the Son’s filial relationship to the Father. There is “reciprocity” and equality among the Persons, but the relations within that reciprocity are not identical.
The “harmonic essence” of chords reflect “Augustine’s unity of the Divine substance and the unity of the Triune God expressed in Athanasius’ words as ‘The Father does all things through the Word in the Holy Spirit’” (155). Music is also Thomistic, as it underscores Thomas’s “point that relation in God is the same as God’s essence and that there are three distinct oppositions relations: Fatherhood, Sonship and Love constituting the Divine Persons” (155).
She thinks that music can prove modalism “wrong.” Again, it’s too much to say that music poses an argument for or against a Trinitarian formulation, but her point stands: “The threeness of the persons is affirmed symbolically in the make-up of the chord.” Even when a single note is played, “the other notes of the chord may be discerned as sympathetic notes,” so that, contrary to the modalist notion that a singular person acts in three different ways, music provides a model for understanding how there are three in every ad extra operation.
Music is also more consistent with orthodoxy than with subordinationism, since each note equally form the triadic chord. And she thinks that “the musical symbolism also runs counter to the theory of the Adoptionists” (155), though she doesn’t explain how.