A Dictionary of Music and Musicians/Lydian Mode
LYDIAN MODE. (Lat. Modus Lydius, Modus V, Tonus V.) The Fifth of the Ecclesiastical Modes; called, by mediæval writers, Modus lætus, (The Joyful Mode,) from its generally jubilant character.
The Final of the Lydian Mode is F: and its compass, in the Authentic form, lies between that note, and the octave above. Its semitones fall between the fourth and fifth, and seventh and eighth degrees. Its Dominant is C; its Mediant, A; and its Participant G. Its Conceded Modulations are, B, D, and E; and its Absolute Initials, F, A, and C.
Mode V.
In the Plagal, or Hypolydian form, (Mode VI,) its compass lies between the C below the Final, and the C above it: and its semitones fall between the third and fourth, and seventh and eighth degrees. The Final of the Hypolydian Mode is F; its Dominant is A; its Mediant is D; its Participant, the lower C. Its Conceded Modulations are B (the 7th), B (the inverted 7th), and G: the two B's being frequently made flat, to avoid the Tritonus. [See Modes.] Its Absolute Initials are C, D, and F.
Mode VI.
The Fifth Mass in Palestrina's Tenth Book—Missa Quinti Toni—is written, as its name implies, in the Lydian Mode. A beautiful example of the use of the Hypolydian, and one which fully justifies the epithet antiently applied to it—Modus devotus (The Devout Mode)—is to be found in the first movement of the Plain Chaunt Missa pro Defunctis, printed, at length, in the article, Kyrie.
The Lydian Mode of the Middle Ages has nothing, but its name, in common with the older Greek scale, which is said, on the authority of Apuleius, and other antient authors, to have been characterised by a tone of soft complaint—a peculiarity which modern poets have not forgotten, in their allusions to it.