The legend that Terpander rejected "four voiced song" in favor of new songs on the seven-stringed lyre epitomizes a confrontation between two musical traditions during the Greek Orientalizing period (c. 750-650 B.C.), catalyzed by the westward expansion of the Assyrian empire. The seven-stringed lyre answers clearly to the heptatony which was widely practiced in the ancient Near East, as known from the diatonic tuning system documented in the cuneiform musical tablets. "Four voiced song" must be understood as describing the inherited melodic practice of the Greek epic singer.
The hypothesis of the syncretism of these two musicstreams can be tested against the evidence of the extant Greek theorists and musicographers. Here we find fundamental differences between the Mesopotamian and Hellenic traditions. Though diatonic scales were also known in Greece, even the late theorists remembered that pride of place was given to other forms of heptatony, the chromatic and enharmonic genera -- tone structures which cannot be established solely through the consonant intervals of the diatonic method. Nevertheless, these tunings were consistently seen as modifications of the diatonic -- which Aristoxenus believed to be the "oldest and most natural" of the genera -- and were required to conform to minimum conditions of diatony. Thus the genera may be explained, at least in part, as native microtonal inflections superimposed on a borrowed diatonic substrate to create distinctly Hellenic forms of heptatonic music.