Another peculiar form, practically the antithesis of the sequence in its origin, is the trope, which consists of the dilation of the musical or the literary text by the interjection of complementary phrases. This—at least at first—was probably done to avoid monotony. For instance, instead of singing Kyrie eleison nine times in succession, it was sung as follows:
‘Kyrie cuncti potens genitor Deus, omni creator eleison—fons et origo boni pie luxque perennis, eleison.
Kyrie salvicet pietas tua nos, bone rector, eleison,’ etc.
(Tutilo, Cod. S. Gall, 484.)
All parts of the mass, from the Introit to the Communion, have been decorated with tropes. There has been compiled a list of seventy-eight tropes for the Kyrie alone. Like the sequence the trope developed from an accessory function to an independent form which at one time was practised with much assiduity.
V
Whether the musical theory of the ecclesiastical chants prior to the fifth century—apart from the Ambrosian hymns—was influenced more by Roman or Oriental traditions is a moot point. The question, however, is not vital, as the real founder of the church system of modes, the Pythagorean philosopher Boethius (fifth century), was professedly an imitator of the Greek theorists. Boethius speaks of the ancients with something like veneration, and takes pride in writing like a Greek, after the fashion of Plato, Aristotle, Aristoxenus, Nichomachus, Philolaus, and Ptolemy. He is a mathematician rather than a musician. He congratulates Ptolemy on having ignored the testimony of the ear and condemns the practice of music as interfering with the just and logical consideration of theory. Cassiodorus and Isidore of Seville speak in somewhat the same fashion. Boethius is the authority for a long line of church musicians, including Hucbald, Guido, Englebert, Jean de Muris, Adam de Fulda, and Alcuin. The mathematical view of music fathered by him gained such prevalence that in the curriculum of mediæval universities music was placed among the mathematical sciences.
We cannot do more here than briefly indicate the tone system used in the church after the liturgy had been definitely formulated, without going into the question of its earlier evolution. The system of modes was professedly founded on the tetrachordal species of the Greeks (see Chap. IV, p. 112), but with an obvious misunderstanding of the Greek system. At first only four forms were recognized, namely, the so-called authentic (from [Greek: ], to govern) modes of St. Ambrose. According to tradition St. Gregory added to these four ‘plagal’ (from [Greek: plagios], oblique). At any rate before the eleventh century there were eight accepted church modes, four ‘authentic’ modes, and four ‘plagal’ or derived modes. Later theorists taught the existence of fourteen different scales. Two of these were rejected as ‘impure’; the other twelve remained in use for centuries, and were known by the names of their Greek prototypes, but these names, too, were misapplied, as will be seen from the following table, where the octave D-d corresponding to the Phrygian species of the Greeks is named Dorian, and vice versa the octave F-f (Greek mixolydian) has become the Lydian, and so forth. The difference between authentic and plagal modes was chiefly one of range and emphasis. For example, in every mode two tones were considered, and were, as a matter of fact, of predominant importance; the final or note on which the piece ended, somewhat analogous to our tonic or key-note, and the dominant, the note most frequently touched in the course of the melody, the centre of gravity, so to speak, about which the melody moved. In the authentic modes the melody never sank below the final except in cadence, where it might take the note immediately below the final and rise by one step to the close; and the dominant was, like our dominant, in the middle of the scale. In the plagal modes, on the other hand, the melody wandered freely as low as a fourth below the final, which thus was near the middle of the melodic range; and the dominant was a third below the dominant of the corresponding authentic mode. Whenever the dominant fell on B, C was substituted (indicated by N.B. in the table) and in the rejected Locrian G was substituted for F.
Each authentic mode had its related plagal. The final of the ecclesiastical Dorian mode was D.[63] The range of a melody written in this mode was limited to notes which may be represented on the pianoforte by the white keys between D and d, including the two D’s and, for the cadence, the C below the lower. The melody would centre about A and come to end on D. The related plagal mode, called the Hypodorian, had the same final, D, but the range of a melody in this mode was from the A below to the A above the final, centering about the dominant, F. The so-called relaxed modes which are frequently met with varied likewise from the authentic modes in range which in such modes might be extended to a third below the final. The dominant remained the same and the slight extension of range hardly altered the ethos or character of the authentic mode from which it thus technically varied.