A Dictionary of Music and Musicians/Plagal Modes

by William Smyth Rockstro

PLAGAL MODES (Lat. Modi plagales; Gr. πλάγοι ἧχοι^[1]; Germ. Plagaltöne, Seitentöne, Nebentöne). When the Plain Chaunt Melodies were first reduced to systematic order, traditionally by S. Ambrose, Bishop of Milan, towards the close of the 4th century, four Modes only were in use—those beginning and ending on the notes now called D, E, F, and G. These venerable Scales, known as the 'Four Authentic Modes,' were named and numbered, in imitation of certain still more antient Greek tonalities from which they were more or less directly derived. Thus, the first, having D for its Final, was called 'Authentus primus,' or, the 'Dorian Mode'; the second, with E for its Final, 'Authentus deuterus,' or, the 'Phrygian Mode'; the third, with F for its Final, 'Authentus tritus,' or, the 'Lydian ^[2]Mode'; the fourth, with G for its Final, 'Authentus tetrardus,' or, the 'Mixolydian ^[3]Mode.' And the compass of these Modes was sufficiently expended to include that of all the Ecclesiastical Melodies then in common use.

Some two hundred years later—if tradition may be trusted—S. Gregory added to these Modes four others, directly derived from them, and hence called Plagal Modes (from πλάγιος, oblique, borrowed). These supplemental Scales involved no new combinations of Tones and Semitones. They were simply formed by enlarging the compass of the Authentic Modes, downwards, to the extent of a Perfect Fourth, the three upper notes being removed, in order that the compass of the Scale might still be comprised within the limits of an Octave, while the Final remained unchanged. This will be readily understood, if we bear in mind that every Authentic Scale consists of a Perfect Fifth, and a Perfect Fourth, the Fourth being placed above the Fifth, and beginning on the note on which the Fifth ends. [See Modes, The Ecclesiastical.] Thus, the First, or Dorian Mode, consists of a Fifth, D, E, F, G, A, surmounted by a Fourth, A, B, C, D. Now, if we add an A, B, and C, beneath the lower D, and compensate for this extension by removing the upper B, C, and D, we shall produce a Scale consisting of a Perfect Fourth, A, B, C, D, surmounted by a Perfect Fifth, D, E, F, G, A; and this Scale will be the Plagal form of the Dorian Mode, and will serve as the type of all similar derivations, as may be seen from the following examples:—

Dorian.

Phyrgian.

Lydian.

Mixolydian.

The number of the Modes being thus increased to eight, a new form of nomenclature was naturally demanded for them, while a new system of numbering became still more imperatively necessary. The change of nomenclature was easily arranged. In order to prevent unnecessary confusion, the old names Dorian, Phrygian, Lydian, and Mixolydian, were still retained for the Authentic Modes, while the Plagal forms were distinguished from them by the addition of the prefix Hypo (under), the new Scales being called the Hypodorian,^[4] Hypophrygian,^[5] Hypolydian, and Hypomixolydian,^[6] Modes. On the other hand, it was indispensable that the numbers of the Modes should be entirely changed; the Phrygian becoming the Third Mode, instead of the Second; the Lydian, the Fifth; and the Mixolydian, the Seventh: the Second, Fourth, Sixth, and Eighth places, being reserved for the newer Plagal forms.

The next great change was the introduction of two new Authentic Modes, called the Æolian, and the Ionian,^[7] having A and C for their Finals, and naturally giving rise to two new Plagal forms, entitled the Hypoæolian,^[8] and Hypoionian,^[9] and lying between E and E, and G and G, respectively.^[10]

Æolian.

Ionian.

The precise time at which these new Modes were brought into general use cannot be ascertained; but we hear of them, with certainty, as early as the reign of Charlemagne (ob. 814) though the earliest exhaustive account of the entire system bequeathed to us is that contained in the Dodecachordon of Glareanus, published in 1529. The learned author of this invaluable work insists strongly upon the use of twelve distinct tonalities, and prefaces his volume with a list of them, divided into two parallel columns, he first of which contains the Plagal, and the second the Authentic Modes, arranged in their natural order, the series being supplemented by rhe rejected Hyperæolian Mode,^[11] having B for its Final, and its Plagal derivative, the Hyperphrygian,^[12] with the necessary caution, sed est error.^[13]

The completion of the Gregorian system by the addition of the Æolian and Ionian Modes, with their respective Plagals, was productive of very important results, and enriched the series with the capability of introducing a far greater amount of varied expression than is apparent at first sight. Some writers have objected to them, on the ground that they are in reality no more than unnecessary reduplications of already existing Scales, since, in its compass, and the disposition of its Semitones, the Æolian Mode corresponds exactly with the Hypodorian, the Hypoæolian with the Phrygian, the Ionian with the Hypolydian, and the Hypoionian with the Mixolydian.^[14] By parity of reasoning, the Hypomixolydian Mode should also be regarded as superfluous, since its compass, and Semitones, correspond precisely with those of the Dorian. But a little consideration will prove this argument to be utterly fallacious. In all that concerns expression, the Eighth Mode differs, toto cœlo, from the First; for its Final—the note to which the ear is constantly attracted—lies in the middle of its series of sounds, whereas, in the Dorian Mode, it occupies the lowest place. This peculiarity invests all the Plagal Modes, without exception, with a character entirely different from that which distinguishes the Authentic series; a fact which was so well known to the earlier writers on the subject that they assigned to each Mode a special epithet descriptive of its æsthetic peculiarities, Thus, the First Mode was called 'Modus Gravis,' the Second, 'Modus Tristis,' the Third, 'Modus Mysticus,' the Fourth, 'Modus Harmonious,' the Fifth, 'Modus Lætus,' the Sixth, Modus Devotus,' the Seventh, 'Modus Angelicus,' and the Eighth, 'Modus Perfectus.'^[15] On carefully examining this classification, we shall find that the Plagal Modes are everywhere characterised by a calmer and less decided force of expression than their authentic originals; thus, while the latter are described as Grave, Mystical, Joyful, and Angelic, the former are merely Sad, Harmonious, Devout, and Perfect. The solemn grandeur of the First 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.'

Mixed Melody. 'Jock o' Hazeldean.'

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.'^[16] 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.

[ W. S. R. ]

1. In contradistinction to the κυριοι ἧχοι, or Authentic Modes.
2. The Hyperphryglan of Martianus Capella. Called, also, by those who contend for the purely Greek origin of the Ecclesiastical Modes, the Æolian; the true Greek Lydian being a whole Tone higher than, the Phrygian, and not, as in this case, a Semitone.
3. The Hyperlydian of Capella.
4. The Hypermixolydian of Ptolemy.
5. The Hyperæolian of Capella.
6. The Hyperiastian, or Hyperionian, of Capella.
7. So called by Porphyrius. By Apulelus and Capella called the Iastian.
8. The Hyperdorian of Capella.
9. The Hypoiastian of Capella.
10. In the Ecclesiastical Music of the Eastern Church, nine Modes only re admitted, under the following titles:
    1. Dorian (α′).
    2. Hypodorian (πλάγιον α′).
    3. Phrygian (β′)
    4. Hypophrygian (πλάγιον β′).
    5. Lydian (γ′).
    6. Hypolydian (πλάγιον γ′).
    7. Mixolydian (δ′).
    8. Hypomixolydian (πλάγιον δ′).
    9. Æolian.
11. More generally known as the Locrian Mode.
12. The Hyperlydian of Politianus; but now more generally known as the Hypolocrian.
13. It is probable that this caution is directed only against Politian's method of nomenclature; but it is equally applicable to the Mode itself, which is utterly discarded by the Great Masters.
14. The later editors of Proske's 'Musica Divina,' adopting this erroneous theory, have described Palestrina's Missa Papæ Marcelli' as beinh written in the Mixolydian Mode, whereas it is really in the Hypoionian. In this particular ease, even Balul has fallen Into an error which Proske, himself the most conscientious of editors, was always careful to avoid.
15. Figulus interprets the sentiment of the Modes somewhat differently—in the case of the First Mode, with a very wide dlfferenco indeed. His epithets are. i. Hilaris; ii. Mœstus; iii. Austerus; iv. Blandus; v. Jucundus; vi. Mollis; vii. Gravis; viii. Modestus. The difference of sentiment between the Authentic and Plagal Modes is even more strongly set forth here than in the more generally-received synopsis given above, in the text.
16. '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.)