The word tonos occurs several times in Aristotle with the sense of 'pitch,' but is not applied by him to the keys of music. The nearest approach to such a use may be found in a passage of the Rhetoric (iii. 1, p. 1403 b 27).

Speaking of the rise of acting (hypokrisis), which was originally the business of the poet himself, but had grown into a distinct art, capable of theoretical as well as practical treatment, he observes that a similar art might be formed for oratory. 'Such an art would lay down rules directing how to use the voice so as to suit each variety of feeling,—when it should be loud, when low, when intermediate;—and how to use the keys, when the pitch of the voice should be high or low or middle (kai pÔs tois tonois, oion oxeia kai bareia kai mesÊ, sc. phÔnÊ); and the rhythms, which to use for each case. For there are three things which men study, viz. quantity (i. e. loudness of sound), tune, and rhythm (tria gar esti peri hÔn skopousi, tauta d' esti megethos, harmonia, rhythmos).' The passage is interesting as showing the value which Aristotle set upon pitch as an element of effect. And the use of harmonia in reference to the pitch of the voice, and as virtually equivalent to tonos, is especially worthy of note.