A Dictionary of Music and Musicians/Locrian Mode
LOCRIAN MODE (Lat. Modus Locrius, Modus Hyperæolius). The Eleventh Ecclesiastical Mode: a tonality which can scarcely be said to have any real existence—as it is universally discarded, in practice, on account of its false relation of Mi contra Fa—though, in theory, it necessarily takes its regular place in the series. [See Mi contra Fa.]
Theoretically, the Final of the Locrian Mode is B. Its compass, in the Authentic form, ranges between that note, and its octave above; and its semitones lie between the first and second, and third and fourth degrees. Its Dominant is G, (F being inadmissible, by reason of its forbidden relation with the Final,) and its Mediant, D. Its Participants are E, and F; its Conceded Modulations, C, and the A below the Final; and its Absolute Initials, B, C, D, and G.
Mode XI.
In its Pagal, or Hypolocrian form, (Mode XII,) its compass lies between F and the F above; and its semitones fall between the fourth and fifth and the seventh and eighth degrees. Its Final is B; its Dominant, E; and its Mediant, D. Its Participants are G, and C; its Conceded Modulations, A, and the upper F; and its Absolute Initials, G, A, B, C, D, and E.
Mode XII.
It will be observed that the actual notes of Modes XI and XII correspond, exactly, with those of Modes IV and V. The reason why the two former are discarded, and the two latter held in good repute, is this. Mode IV, being Plagal, is subject to the 'Arithmetical Division'; i.e. it consists of a Perfect Fourth, placed below a Perfect Fifth. But, Mode XI is Authentic; and, by virtue of the 'Harmonic Division,' consists of a Quinta falsa, placed below a Tritonus—both of which intervals are forbidden, in Plain Chaunt. Again, Mode V, being Authentic, and therefore subject to the 'Harmonic Division,' resolves itself into a Perfect Fifth, below a Perfect Fourth. But, Mode XII is Plagal; and, under the 'Arithmetical Division,' exhibits a Tritonus, below a Quinta falsa. [See Modes, the Ecclesiastical.]
A very few Plain Chaunt Melodies, and Polyphonic Compositions, are sometimes referred to these rejected Modes: but, such cases are exceedingly rare; and it will generally be found that they are really derived, by transposition, from some other tonality.