Authentic mode

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An authentic mode is one of four Gregorian modes whose final (or "tonic") is the lowest note of the scale (apart from the possibility of one "added note" below). Given the natural diatonic scale/mode of C Major, these four authentic modes are the ones that start on D (Dorian), E (Phrygian), F (Lydian), and G (Mixolydian).

The other four Gregorian modes are the plagal modes, and differ from the authentic modes in their range and reciting tones.

The repertory of Western plainchant acquired its basic forms between the sixth and early ninth centuries, but there are neither theoretical sources nor notated music from this period. By the late eighth century, a system of eight modal categories, for which there was no precedent in Ancient Greek theory, came to be associated with the repertory of Gregorian chant. This system likely originated from the medieval Byzantine oktōēchos, as indicated by the non-Hellenistic Greek names used in the earliest Western sources from about 800 (Powers 2001, §II.1(ii)). Ignorant of these developments, Hucbald (840-930) created a series of 8 modes, separated into two pairs: Authentic and Plagal modes.^{[citation needed]} The authentic modes were the odd-numbered modes, 1,3,5,7. The tenor, or dominant (corresponding to the "reciting tone" of the psalm tones), is a 5th above the final of the scale, with the exception of mode 3 (Phyrigian), where it is a 6th above the final. This is because a 5th above the tonic of mode 3 is the "unstable" B/B♭.

For more information, see musical mode.

References

• Powers, Harold S. (2001). "Mode". The New Grove Dictionary of Music and Musicians, edited by Stanley Sadie and John Tyrrell. London: Macmillan.