Gregorian mode

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.

[4] These four modes correspond to the modern modal scales starting on re (Dorian), mi (Phrygian), fa (Lydian), and sol (Mixolydian).

[9] The earliest definition of plagal mode is found in Hucbald's treatise De harmonica (c. 880), who specifies the range as running from the fourth below the final to the fifth above.

[12][page needed] The final is the pitch in which the chant usually ends; it may be approximately regarded as analogous (but not identical) to the tonic in the Western classical tradition.

Likewise the cofinal is an additional resting point in the chant; it may be regarded as having some analogy to the more recent dominant, but its interval from the tonic is not necessarily a fifth.

[13] Given the confusion between ancient, medieval, and modern terminology, "today it is more consistent and practical to use the traditional designation of the modes with numbers one to eight".