Text: "in concord"; relating to that genus or scale employing quarter tones; comprising a major third and two quarter tones also the difference between three conjunct major thirds and an octave (ratio of 125:128); relating to the difference in pitch that results from the exact tuning of a diatonic scale and its transposition into another key. In Greek music the enharmonic genus was the oldest of three ways of subdividing a tetrachord, the other two being the diatonic and the chromatic. In its original form it seems to have consisted simply of a major third with a semitone below, but in quite early times the semitone was divided into two quarter-tones, so that there were four notes in all, instead of three. The existence of these small intervals, which were in use until Hellenistic times, is evidence of the close association between Greek music and Oriental music. In modern acoustics the enharmonic diesis is the interval between an octave, i.e., 2/1; and the three major thirds, i.e., (5/4)3=125/64; B# is therefore flatter than C, and the interval is (2)/125/64=128/125. On keyboard instruments, however, B# and C are identical, and this has encouraged composers to use harmonic changes which exploit this identity, where D# becomes Eflat. Substitution of this kind is known as an enharmonic change. An enharmonic modulation is one which makes use of such a change to facilitate the progress from one key to another. Collin's Music Encyclopedia William Collins Sons, & Co., Ltd., London, 1959.

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