concept in ancient Greek music, pertaining to the placement of scale patterns at different pitches and closely connected with the notion of octave species (q.v.). Through transposition of the Greater Perfect System (comprising two octaves descending from the A above middle C to the second A below) to a higher or lower pitch level, each tonos causes a different octave species to fall within the octave e'-e (E above middle C to the E below), which is important in Greek performance. The names of the tonoi correspond to the names of the octave species that are created between e' and e when the tonoi are used. In effect, a tonos can cause the octave species bearing its name to fall within the e'-e octave. For example, when the Greater Perfect System is begun on the pitch b' (rather than a', as in the abstract), the octave species falling between e' and e is the Phrygian; hence, the tonos is also Phrygian. According to most modern scholars, the tonoi thus render the highly theoretical Greater Perfect System eminently practical in actual performance
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