Eight Modes in Use.—The Church Scales were numbered from one to eight; the Authentic Scales were given the odd, and the Plagal Scales the even numbers, thus:
| 1. Dorian | 2. Hypo-Dorian | |
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| 3. Phrygian | 4. Hypo-Phrygian | |
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| 5. Lydian | 6. Hypo-Lydian | |
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| 7. Mixo-Lydian | 8. Hypo-Mixo-Lydian | |
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A melody in an Authentic Scale had to end on its Keynote, but a melody in a Plagal Scale ended on the Keynote of its related Authentic Scale. Observe that the Dorian and Hypo-Mixo-Lydian Scales are identical; but while the former had to end on the Keynote, D, the latter ended on G, which is the fourth of its scale, and Keynote of its related Authentic Scale.
Traces of these Authentic and Plagal Scales may be found in many old folk-songs. Thus, the melody of the “Last Rose of Summer” begins on the Keynote, rises in the course of the melody to the octave, but ends by falling to the Keynote; it is therefore Authentic. On the other hand, the melody of “Robin Adair” begins on the fourth below the Keynote, rises to its octave, but ends on the fourth above its initial note and is Plagal; thus:
LAST ROSE OF SUMMER. ROBIN ADAIR.
The term Hyper (above) was sometimes applied to the Authentic Scales. In the Greek System the Hyper Scales were the same distance above the standard scales that the Hypo Scales were below. Although twelve modes were theoretically admitted in church music, it was for the most part confined to the eight modes given above.
The Dominant.—In addition to the keynote there was another note in every scale of almost equal importance, called the Dominant. This name has been retained in the modern system, but with a total change of meaning. In the Church Scales it meant the Reciting Note, that is, the note on which the principal part of the words was chanted. In all the Authentic Scales but the Phrygian, the fifth of the scale is the Dominant; in the Phrygian the sixth is the Dominant, because the B was a changeable note, that is, might be natural or flat. The Dominants of the Plagal Scales are a third below the Dominants of the related Authentic Scales, except in the Hypo-Mixo-Lydian, in which the Dominant is a second below that of its related Authentic Scale. Therefore the Dominant is the sixth of all the Hypo Scales, but the Hypo-Phrygian and Hypo-Mixo-Lydian, in which it is the seventh.
Hucbald’s Scale.—Two attempts were made in the 10th century to construct new scales, first by Hucbald, who founded his series of sounds on a tetrachord, in which the halftone was between the second and third, thus: A B C D. His object seems to have been to obtain a series in which a succession of perfect fourths and fifths might be secured, for which purpose he made use of the following series of sounds: