Page:A Dictionary of Music and Musicians vol 2.djvu/353

MODES, ECCLESIASTICAL. varieties; twelve of which remained, for many centuries, in constant use, distinguished by the names of their Greek prototypes, though not really identical with them; while two were rejected, as impure, and practically useless.

Into the laborious process by which these scales were evolved from the complicated mysteries of the Greek Canon we need not enter. To us, their construction is simple enough, when regarded from our own point of view. We have only to imagine a series of the natural notes of the modern Diatonic Scale, extending, upwards, from A, the first space in the bass, to C, the third space in the treble. By dividing this grand scale into sections, each consisting of eight notes, and each beginning with a different sound, we shall obtain the entire set of fourteen Modes, in the most complete form possible.

The Modes are separated into two classes: Authentic, (from, to govern) and Plagal, (from , oblique). The compass of the former extends from the Final (equivalent to the Tonic, or Key-note, of modern theory,) to the Octave above. That of the latter, from the Fourth below the Final, to the Fifth above it. Consequently, the Final is the lowest note of the Authentic Modes; and (very nearly) the middle note of Plagal ones. Every Plagal Mode is derived from an Authentic original, from which it is distinguished, in name, by the prefix, Hypo-: the same Final being common to both forms; and the compass of the derived Mode lying a Fourth below that of the original scale. In the following table, the Final of each Mode is indicated by the letter F; and, the position of the semitones, by a slur.

Each of these Modes is divisible into two members, a Pentachord, and a Tetrachord. The notes which compose the Pentachord are contained within the compass of a Perfect fifth, (Diapente): those of the Tetrachord, within that of a Perfect Fourth, (Diatessaron). In the Authentic Modes, the Fifth is placed below the Fourth: in the Plagal, the Fourth lies below the Fifth. The former is called the 'Harmonic,' and the latter, the 'Arithmetical Division.' In both cases, the highest note of the lower member corresponds with the lowest of the upper: thus—