Now before someone gets their panties in a pinch – let us move on to what Rupert Hughes writes about:

ECCLESIASTICAL MODES

Music, along with all the other early Christian arts, borrowed largely from the Greeks, but rejected their warmth and ornate sophistication for a stark rigidity.

Early church musicians took the Greek modes as best they could understand them, making as many mistakes as was usual in the degenerate classicism of those times. The Byzantine school perverted Greek music and passed it along, as it had done with painting and architecture. The range and the chromatic graces of later Greek melody were deserted for a heavy march through one octave of one key. Furthermore, the scale was considered now as ascending, instead of descending.

St. Ambrose is traditionally credited with establishing four modes for church music. From these St. Gregory was believe to have derived four new modes. The original four are call Authentic, i.e., "governing" or "chief." The latter four are called Plagal, i.e., "oblique" or "inferior." To these were added other modes, some of them being denied a right to exist. As with all the old Greek modes, all the church modes are to be found on the white keys of the piano; no chromatic was allowed except, finally, b flat, which was admitted to avoid the forbidden tritone and the diminished fifth. A melody that did not stray out of its octave mode was called perfect; one that did not use all of its range was imperfect; one that overstepped its octave was superfluous; one that used up both a mode and its plagal was in a mixed mode.

Greek name were used for the church modes, but with many differences from the old nomenclature.

And authentic mode is based on its Final or lowest note; the next most important note, usually a fifth or a third above, is its dominent A plagal mode is found a fourth below its authentic, and the final of the authentic serves also for the plagal. The dominant of a plagal is a third below that of its authentic (save where it falls on b, in which case c is used).

Curiously enough, the two modern keys which we think of as white keys, c major and a minor, were not added until the sixteenth century, and then as the Ionian and AEolian modes.

Besides many impressive hymns the church modes have been unconsciously allowed to fit many popular modern tunes. (Ms. Mary - Here is the answer to your original thread question - ) It is not hard to test the mode-ship of any air. First if necessary, bring the melody into a range requiring no key-signature. If it now contains any accidentals save b flat, it is not in any of the modes. Otherwise note the tone on which the air ends. This will be the final of its mode. If this is the lowest, or almost the lowest note used, and if the melody does not soar higher than an octave above it, the air is in an authentic mode. If the final is in approximately the center of the melodic range, and if the range does not exceed the fifth above, or the fourth below, it is in a plagal mode, or it may be in a mixed mode. The name of the final indicates the mode. The airs "God save the Kind" (or "America") and the "Blue Bells of Scotland" are authentic melodies. The "Old 100th" and "Eileen Aroon" are plagal "Jock o' Hazeldean" is in a modern sense of tonality as our modern music would seem anarchistic to an old master. Superb treasures were given to immortality in those stiff and arbitrary forms. Yet, after all, the modes deserve their eternal obsoleteness. They were unsatisfactory and arbitrary in their own day. They are hopelessly inappropriate to the modern musical ideas and ideals. The majestic beauties of some of their results are but as the impressive fossils of earlier involution. Their fate should warn us against stolid satisfaction with our own musical system.

Sincerely,
RUPERT HUGHES via Gargoyle