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The Greeks knew this diatonic principle of dividing up fourths and fifths, so that a tetrachord spanning the interval e to a might consist straightforwardly of the four notes e f g a (S T T). But they also knew alternative, non-diatonic systems, and in the Classical period these predominated. In such systems the octave contained only one step of a tone, namely the disjunction. The steps within the tetrachords were all either larger or smaller than a tone. This is one reason why it was natural for Greek theorists to see the tetrachord as a unit of analysis. It stood out more clearly than it does in a diatonic scale. |
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The ancients distinguished three 'types' of scale, or 'genera' as it is customary to say, rendering the Greek genos by the Latin genus. The diatonic was one. The other two were called enharmonic and chromatic.1 In the enharmonic, the two inner notes of the tetrachord were crowded down close to the bottom, at intervals of only about a quarter-tone, leaving a wide gap of two tones above them. In the chromatic genus they were again bunched low down, but at intervals of more like a semitone. The wider interval above them was in this case something like a minor third (1 1/2 tones). The pattern of the tetrachord in the three genera was:2 |
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enharmonic e f a
chromatic e f a
diatonic e f g a |
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These are the standard definitions, but the pitching of the inner notes could fluctuate within certain limits. More on this below. |
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Two further points of ancient terminology may conveniently be mentioned here. The outer notes of the tetrachord, which remained fixed in their mutual relationship a fourth apart in all genera and marked out the skeleton of the octave, were called the standing notes, while the inner ones, whose position varied from genus to genus, were called the moving notes. The bunch of three notes close together at the bottom of the enharmonic and chromatic tetrachords was known as the pyknon ('close-packed'). |
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Before we go further, let us see if we can discover what lies behind this odd diversity in the arrangement of degrees of the scale. Ethnomusicology has light to shed on the matter. |
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1 Those familiar with these terms in connection with Western music will note that their meanings have changed since Antiquity. |
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2 The reader is reminded that a small arrow pointing up or down indicates a note raised or lowered by a microtone, that is, an interval less than a semitone. Where no further precision is given it may be taken as more or less a quarter-tone. |
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