Mode gives place to the sadness of the Second; while the joy of the Fifth merges, in the Sixth, into devotion. That this distinction can be in no wise dependent upon the position of the Semitones is evident; for we have already shown that these are similarly placed, in different Modes; it must, therefore, be entirely due to the peculiar aspect of the tonality with regard to the situation of its Final—to the difference of effect produced by a point of ultimate repose placed in the middle of the Scale, as contrasted with that peculiar to one resting on the lowest degree. And a similar difference of expression may be found, even in Sæcular Music, if we only examine it carefully. Take, for instance, the three following beautiful old Melodies, in the Ionian Mode transposed; the first of which lies between the Tonic and its Octave; the second, between the Dominant and its Octave; and the third, between the Dominant, and the Tonic in the Octave above. Is it possible to deny, that, apart from its natural individuality, each of them owes a peculiar character to the position it occupies in the Scale?
Authentic Melody. 'The Blue-Bell of Scotland.'
Plagal Melody 'Aileen Aroon.'
![{ \time 3/4 \key f \major \relative c' { \repeat volta 2 { c4 d e | f4. g8 a4 | c,16 f8. d16 f8. e16 g8. | f2. } a4 a a | c4. c,8 c4 | a' a8[ c] bes[ g] | f4 d c | c' bes8[ a g f] | f4. g8 a4 | c,16 f8. d16 f8. e16 g8. | f2. \bar "||" } }](http://upload.wikimedia.org/score/o/g/ogo95g57pogglv5bpmos8wyk3vnzoq2/ogo95g57.png)
Mixed Melody. 'Jock o' Hazeldean.'
![{ \time 4/4 \key f \major \override Score.Rest #'style = #'classical \partial 4 \relative f'' { \[ f4 | c^\markup { \small Authentic. } a g f \] f a c, d | f_\markup { \small Plagal. } f bes a | a g r \[ f' | c^\markup { \small Authentic. } a g f \] f a c, d | f_\markup { \small Plagal. } a \acciaccatura a8 g4. f8 | f2. \[ f4 bes4. a8 bes4 c | d^\markup { \small Authentic. } c f c | c a g8 a c4 | d2. f4 | c a g f \] | f a c, d | f_\markup { \small Plagal } a \acciaccatura a8 g4. f8 | f2. \bar "||" } }](http://upload.wikimedia.org/score/t/s/tsbzwemn2p2c1g2izzl7rzrd5q64kgh/tsbzwemn.png)
Now, the first of these Melodies, lying entirely between the Tonic and its Octave, is strictly Authentic; the second, lying between the Dominant and its Octave, is strictly Plagal; and the third, occupying the entire range of the Mode, from the Dominant below to the Tonic in the next Octave above, is Mixed. [See Modes, The Ecclesiastical.] Here, then, are three varieties of expression producible by the Ionian Mode alone; and, when we remember the number of Modes, which, in addition to this distinction, obtainable by mere change of position, possess a distinct tonality also, we cannot but be struck with the immense fund of variety with which the Gregorian system is endowed. Moreover, it is not absolutely necessary that the Melody should be restricted to the exact compass of an Octave. Originally, as we learn from Hermannus Contractus, no licence was permitted in this matter; but Theogerus, Bishop of Metz, writing about the year 1100, allows the elongation of the Scale, whether Authentic or Plagal, to the extent of a Tone above, and a Tone below its normal limits. The same licence is permitted by Hucbaldus of S. Amand, and the Abbat Oddo; and it has become a recognised rule that the First Mode may be extended a Tone downwards, and a Tone, or even a Minor Third, upwards; the Second, a Tone downwards, and a Semitone, Tone, or Minor Third, upwards; the Third Mode, a Major Third downwards, and a Semitone upwards; the Fourth, a Tone downwards, and a Semitone upwards; the Fifth, a Semitone, or Minor Third, downwards, and a Tone upwards; the Sixth, a Semitone downwards, and a Tone upwards; the Seventh, a Tone downwards, or upwards; the Eighth, a Tone downwards, or upwards; and so with the later forms; one Degree, either upwards or downwards, being always conceded, and a Major or Minor Third, in one direction, very frequently claimed. Guido d'Arezzo's rule is, that 'Though the Authentic Modes may scarcely descend more than a single Degree, they may ascend to the Octave, the Ninth, or even Tenth. The Plagal Modes, however, may be extended by carrying them down to the Fifth (i.e. below the Final); but authority is granted to extend them (upwards) to the Sixth, or the Seventh (i.e. above the Final) as the Authentic form rises to the Ninth and Tenth.'[1] Here, then, we see a new and prolific source of variety, in the elaboration of which the Plagal Modes play a very important part; an advantage which is turned to equally good account in Plain Chaunt and Polyphonic Music. Indeed, it is perhaps even of greater significance in the latter, than in the former: for, where numerous vocal parts are concerned, the benefit to be derived from an extended Scale is obvious; while, as we have elsewhere explained, where the Tenor, and Cantus, are written in an Authentic Mode, the Bassus and Altus, naturally fall within the compass of the Plagal form, and vice versa. To the Polyphonic Composer, therefore, the use of the Plagal Modes is indispensable.
- ↑ 'Autenti viz a suo fine plus una voce descendunt—Ascendunt autem autenti usque ad octavam et nonam, vel etiam decimam. Plagæ vero ad quintam remittuntur et intenduntur; sed intensioni sexta vel septima auctoritate tribuitur, sicut in autentis nona et decima.' (Discipl. Artis Mus. xlli.)
