Note 6 — § 12. Plutarch's Dialogue on Music.
Reading edition
Aristides Quintilianus uses tropos as the regular word for 'key:' e.g. in p. 136 en tê tôn tropôn, hous kai tonous ekalesamen, ekthesei. So Alypius (p. 2 Meib.) dielein eis tous legomenous tropous te kai tonous, ontas pentekaideka ton arithmon. Also Bacchius in his catechism (p. 12 Meib.) hoi tous treis tropous adontes tinas adousi; Lydion, Phrygion, Dôrion; hoi de tous hepta tinas; Mixolydion, Lydion, Phrygion, Dôrion, Hypolydion, Hypophrygion, Hypodôrion, toutôn poios estin oxyteros? ho Mixolydios, k.t.l. And Gaudentius (p. 21, l. 2) kath' hekaston tropon hê tonon. Cp. Dionys. Hal. De Comp. Verb. c. 19.