A Dictionary of Music and Musicians/Authentic
AUTHENTIC. Such of the ecclesiastical modes are called authentic as have their sounds comprised within an octave from the final. They are as follow, in order of the Gregorian system:—
| No. | Mode. | Compass. | Final. | Dominant. |
| 1 | Dorian | D to D | D | A |
| 3 | Phrygian | E to E | E | C |
| 5 | Lydian | F to F | F | C |
| 7 | Mixolydian | G to G | G | D |
| 9 | Æolian | A to A | A | E |
| 11 | Ionian or Instian | C to C | C | G |
A mode, or tone, or scale, must be made up of the union of a perfect fifth (diapente) and a perfect fourth (diatessaron). In the authentic modes the fifth is below, and the fourth above. Thus in mode 1 from D to A is a perfect fifth, and from A to the upper D, or final, a perfect fourth. In mode 9, from A to E is a perfect fifth, and from E to the upper A, or final, a perfect fourth, and so on.
In all these the fifths and fourths are perfect; but no scale or mode could be made upon B in conformity with this theory, for from B to F is an imperfect fifth and from F to the upper B is a tritone or pluperfect fourth, both which intervals are forbidden in the ancient ecclesiastical melody. This may serve also to explain the irregularity of the dominant of the third mode. In all the other authentic modes the fifth note of the scale is the dominant; but in the third mode, the fifth being B, and consequently bearing forbidden relations with F the fourth below it and F the fifth above it, B was not used, but C the sixth was substituted for it as the dominant. It is to be borne in mind that melodic and not harmonic considerations lay at the foundation of all these rules, and that the 'dominant' then meant the prevailing or predominant sound in the melody of the tone or scale. The prefix hyper (or over) is often added to the name of any authentic mode in the sense of upper, to distinguish it from the corresponding plagal mode, to which the word hypo (under or lower) was prefixed. Thus while the authentic Dorian or hyperdorian scale ran from D to D, its plagal, the hypodorian, began on the A below and ran to its octave, the dominant of the authentic scale. 'Ein feste Burg' and 'Eisenach' are examples of 'authentic' melodies, and the Old 100th and Hanover of 'plagal' ones. [Gregorian Tones.]
The meaning of the term 'authentic' is variously stated. It is derived from the Greek verb αυθεντέω, to rule, to assume authority over, as if the authentic modes ruled and had the superiority over their respective plagal modes. They are also called authentic as being the true modes promulgated by the authority of St. Ambrose; or as authentically derived from the ancient Greek system; or as being formed (as above stated) of the perfect diapente (or fifth) in the lower, and of the perfect diatessaron (or fourth) in the upper part of their scales, which is the harmonic division, and more musically authoritative than the arithmetical division which has the fourth below and the fifth above.