Modes

MODI. – The word m. in music is used both in rhythm and in harmony.

1) In the rhythmic sense, in the music of the 12th and 13th centuries, it refers to the six metrical schemes taken from classical prosody (trochaic, iambic, dactylic, anapaestic; less frequently, spondaic and tribrachic), on which the « troubadours » modelled their songs. It is also applied to the duration value chosen as the unit: modus maior, represented graphically by the maxima, and modus minor by the longa (both completely blackened); modus perfectus, ternary, and modus imperfectus, binary. The mensural sign often indicates (a closed circle for the perfect m., a semicircle for the imperfect m.) the nature of the measure chosen. This system is found in the music of the 15th and 16th centuries, written according to proportional notation. 2) In the harmonic sense, modern music recognizes two m.: major and minor, distinguished by the position of the two semitones in the eight-note scale: in the major, the first semitone is two whole tones distant from the fundamental, whereas in the minor it is a tone and a half distant. The keys are merely transpositions of the two major and minor modal successions. 3) By confusion, one speaks of ecclesiastical or Gregorian « tones », whereas correct terminology adheres to the word « m. » for the harmonic systems underlying the monophonic compositions of both Greek music and medieval Western liturgical and secular music.

Until the first decades of the 20th century, the question of the Gregorian m. seemed to have been resolved by the explanation of « complete and homogeneous » scales of eight notes. Discussion concerned only the number of these scales, their Greek or Oriental origin, whether they possessed a character of their own, and from which modal scale the modern major and minor had arisen. The Gregorian studies undertaken by the Solesmes school have brought other problems to the fore and proposed objective solutions that are not negligible, even if not entirely definitive. The first aspect of the modal question is summed up under the generic term traditional theory (classical theory or theory of the octoechos); by contrast, the questions that arose from approximately 1920 onward generally fall within the framework of modern theory or hexachordal theory.

I. TRADITIONAL THEORY

The theory of the eight modes, as it can be reconstructed from the writings of medieval authors, may be reduced to a few points. Although it is possible to construct a diatonic scale on each of the seven degrees of the scale, only four fundamentals are nevertheless counted: the famous tetrachord of the finals, re mi fa sol, respectively for the modes protus, deuterus, tritus, and tetrardus. Each of the scales results from the coupling of a fixed pentachord and a movable tetrachord: re-la + la-re, in protus. The mobility of the tetrachord above or below the pentachord makes possible the twofold form, authentic and plagal, of each of the four scales, which always retain the same final or fundamental; thus the authentic protus, 1st mode, extends from the low re to the high re, whereas the plagal protus, 2nd mode, runs from the low la to the high la; they are not two different scales, but two forms of the same scale, since the final is identical, namely re in both cases; the difference is that a plagal melody unfolds in the lower part of this scale, whereas an authentic melody prefers the upper part. The ancient theorists did not have as clear a concept as the moderns of the existence and function of a dominant: modern followers of the traditional system have regarded the eight tenors (reciting tones) of the psalmic formulas la fa do la do la re do as constitutive data; they introduced new elements by asserting the presence of the harmonic dominant (the fifth) not only in the authentic modes, but also in the plagal modes; they applied to the repetition of the final in the upper octave of the authentic modes the same resting property of the final as at the base of the scale, so that Gregorian melodies would exhibit a twofold law: 1) attraction toward the extreme notes as centers of repose (tonic-final-fundamental) in the authentic modes; 2) repulsion from the extremes toward the center in the plagal modes.

Although the final notes are re mi fa sol, some melodies in the current editions, and many more in the diastematic manuscripts, cadence, definitively or provisionally, on the other three higher notes, namely la si do. Perhaps in order not to multiply the psalmic formulas, but above all because the determination of a melody’s mode was made by taking into account only the species of the fixed pentachord (or tetrachord), the theorists did not hesitate to classify melodies ending on la si do as protus, deuterus, and tritus, despite the difference in harmonic constitution from the modes of re mi fa. The greater importance attributed to the basic tetrachord is confirmed by the few examples of modal analysis left by Ubaldo (Gerbert, Scriptores ecclesiastici de musica sacra, I, St-Blasien 1784, p. 140) and by Regino of Prüm (ibid., I, p. 231), who identify the modulations by referring to modal formulas; these formulas characteristic of the mode never attain the extent of an octave, generally content themselves with a single semitone, and go only slightly beyond the limits of the tetrachord.

The name octoechos given to the theory of the eight modes suggests, together with other terms and features, a Byzantine importation into the Western system. Both the Byzantine and Western modal systems, as well as the traditional and modern theories, are indebted to the Greek musical modes, at least insofar as they share the same basis, namely the tetrachord. In Gregorian chant itself, the melodies of deuterus (3rd and 4th modes, with final mi and harmonic division of fourth plus fourth, with la, the ancient “mese,” as central pivot) may, without excessive boldness, be connected with the Greek Dorian mode.

Table of the eight modes according to traditional theory.

II. MODERN THEORY OF THE THREE HEXACHORDS

Proceeding exclusively from the analysis of the melodies published in the Vatican edition of 1905 and 1907, Fr. J. H. Desroquettes, a monk of Solesmes, was the first to affirm the existence of three groups of modal cadences in which the ancient melodist selected the harmonic material of his compositions.

He was followed in the organization of the new theory by Prof. H. Potiron, organist, composer, and theorist, and by Abbot Sufiol. The justification and explanation of the new system rests above all on the observation that medieval copyists support the cadences of protus on re, on sol (with B-flat), and on la; the cadences of deuterus on mi, on la (with B-natural); the cadences of tritus on fa, on B-flat, and on do; and the cadences of tetrardus on sol and do. A cadence note with a few intervals above and below it is sufficient to specify one of the four m., which will subsequently be authentic or plagal, depending on whether the greater development lies above or below the fundamental; in a modal system understood in this sense, there is only one semitone: the appearance of a new semitone almost automatically determines a modulation: tonal, if in the new hexachord one remains in the same m.; tonal and modal, if in the new hexachord one also changes the m.; e.g., if, while leaving protus on re (natural hexachord), one modulates to a cadence on la at the fifth, with B-natural, one passes into the hard hexachord and remains in protus; if one proceeds to cadence on B-natural, the modulation is tonal (from the natural to the hard hexachord) and modal (from protus to deuterus). In addition to the appearance of a new semitone, insistence on intervals characteristic of an m. and a cadence outside the tetrachord of the modal notes likewise determine modulations.

The essential difference between this system and the traditional system consists in abandoning the classical structure of pentachord plus tetrachord, that is, the scale of seven consecutive diatonic notes. At the outset, traditional theory was nothing more than an easy method of classification; modern hexachordal theory claims more: it wishes to discover the modal principle of Gregorian melodic composition. Whereas traditional theory still distinguishes, like the Greeks, the various types of tetrachords (Dorian, Phrygian, Lydian), modern theory, while always speaking of tetrachords, practically disregards the ancient distinction, since the tetrachord of the modal notes is not organic: in fact, each of the four notes may be final; but mi (la in the soft hexachord, B in the hard hexachord), even if it is final, will not be regarded as fundamental; moreover, the other three finals and fundamentals are not the starting point of a tetrachordal system subsequently recognizable in the melodies. Thus, the three tetrachords do-re-mi-fa, re-mi-fa-sol, mi-fa-sol-la are not distinguished; rather, it is the single tetrachord do-re-mi-fa that is repeated three times in the tonal diagram.

The importance of modern theory is brought out by the ease and coherence with which Gregorian melodies can be analyzed; on the other hand, it is believed that this system does not disfigure the modal character of the melodies that one wishes to accompany: accompaniment can and must thus follow more closely the continuous coming and going of the melody, which is almost never fixed either in an m. or in a tone; traditional theory is less conscious of this.

Scheme of the 4 modal cadences in the 3 hexachords.

The ethos, that is, the expressive character of the individual Gregorian m., cannot be determined a priori: ancient and modern theorists do not agree on the particular psychological effect to be attributed, for example, to a 2ᵃ or a 5ᵃ m. The most varied texts and the most opposed sentiments can be musically rendered in each of the eight m.; joy is not always and exclusively illustrated by melodies of the 5ᵃ m., nor sadness by melodies of the 2ᵃ m. It is true that a clearly defined modal system modifies the expression of a given sentiment and depicts it in its own colors, but in Gregorian melodies, even in their most archaic form, frequent modulations at every moment mitigate the dominant impression that would result from the prevalence of one m. over the others.