Authentic mode

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An authentic mode is one of four Gregorian modes whose tonic is the first note of the scale. These four modes correspond to the modern modal scales starting on D (Dorian), E (Phrygian), F (Lydian), and G (Mixolydian).

The other four Gregorian modes are the plagal modes.

Originally thought up by Anicius Manlius Severinus Boethius (480-524), who came up with the idea of Greek musical modes, but almost by merely guessing.

However, Hucbald (840-930) saw Boethius's modes a created a series of 8 modes, separated into two pairs: Authentic and Plagal modes. The Authentic modes were the odd modes, numbered 1,3,5,7. The reciting tone, or dominant, is always a 5th above the tonic or first note of the scale, with the exception of the Phyrigian mode, which is a 6th above the tonic. This is because a 5th above the tonic of the Phyrigian mode is b, which was considered dissonant to the early Roman Church, as an accidental use of this note produced the dreaded tritone.

For more information, see musical mode.