4 Pure Counterpoint Each plagal mode is one degree flatter in The other important note of each mode is the sound than its authentic partner. For instance, the reciting tone, which is used in psalmody. authentic Mixolydian goes: G, A, B, C, D, E, F, G: The actual names of the Gregorian modes were , , , , , , , . The plagal form of the Mixo- taken from Greek music theory. However, there lydian, known as the Hypomixolydian goes: D, E, are many differences in the structure and em- F, G, A, B, C, D: , , , , , , , . Notice that ployment of the modes between antiquity and this is the same range, or ambit or ambitus, as the their uses in the Medieval and Renaissance eras. Dorian mode, but the final is G, not D. Again, the Such relationships thus really exist in name only. Hypomixolydian and Dorian scales have the same Gregorian modes are given the Arabic numbers as root, but each has its own final. found in the Liber Usualis (LU), the largest, most The plagal modes, as partners to the authentics common collection of chant (also known as plain- through sharing the same finalis, could be thought song). The authentics have odd numbers (1, 3, 5, 7) of as adjustments of the original mode to a differ- and the plagals have even ones (2, 4, 6, 8). Every ent range or register, or as the same mode in either polyphonic piece from the Renaissance is in a sin- authentic or plagal position. However, each of the gle mode from beginning to end; there is no such eight Gregorian modes has its distinctively indi- thing as modulation in these works. Be aware that vidualistic character. Such qualities are based in in counterpoint writing and analysis the mode part on the sound of the scale over its own root, in number for each part is always placed in the left part on the relationships of the two tetrachords, margin of the first line of music. By tradition, the and in part on the location of the final itself. range and final of the Tenor voice provide the of- ficial mode name for any composition. Example 2 The Eight Gregorian Modes Mode 1, the Dorian, final D to D. Its lower tet- upper tetrachord is Phrygian (E, F, G, A). It is thus rachord (D, E, F, G) and its upper tetrachord (A, B, slightly flatter in sound than the authentic Dorian, C, D) are intervallically the same: both are the mi- since the scale possess a low sixth degree: , , , nor variety. This is the most popular and harmon- , , , , . It is the equivalent to the natural mi- ically neutral of all the modes. It is minor sound- nor, or pure minor, found in tonality. The reciting ing, but with a high sixth degree: , , , , , , tone is F. , . Both its confinal and its reciting tone are A. Mode 3, the Phrygian, final E to E. Like the Dori- Mode 2, the Hypodorian, A to A, final D. Its an, both its tetrachords are the same, in this case, lower tetrachord (A, B, C, D) is minor, while the Phrygian: (E, F, G, A) and (B, C, D, E). But unlike .