Jablonski, Marek (Michael)


‘Speculum musice’: books 6–7



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3. ‘Speculum musice’: books 6–7.


In the prologue to book 6 Jacobus announced a shift of emphasis, from speculative music as represented by Boethius to practical music: the modes or tones both ancient and modern; their differentie; psalm tones; music and the many things necessary for performing skilfully. Since Boethius derived the modes from octave species Jacobus began with an account of the species of octaves, 5ths and 4ths. To the classical account of eight modes he appended Guido's description of the 1st, 2nd, 3rd and 4th modes of medieval chant. This treatise on the modes or tones according to Boethius concludes with an account of the Greater Perfect System, Greek note names and the 8th (Hypermixolydian) mode added by Ptolemy.

The treatise on ecclesiastical modes opens with a monochord description and an account of tetrachords and species according to Guido and his followers. A curious chapter compares these to metrical feet (T = long, ST = short, thus e.g. T ST represents a trochee). An explanation of the terms modus, tropus and tonus as applied to intervallic constructions is extended to a parallel between music and rhetoric. The eight church modes are described with their regular and irregular finals. In the chapter on affinities (by 4th, 5th and octave) Jacobus twice referred to Liègeois practice. The structure and range of each of the eight modes is described in detail according to Guido, after which the modes are compared by their species construction and their use of B/B. Hexachords are described with natural and irregular mutations. The final portion of book 6 is largely concerned with notation and chant repertory: systems of letter notation; modal structure and chants ending in C or A. A tonary gives examples of differentie, psalm tones, antiphons and mass chants according to the ecclesiastical modes. Characteristic opening formulae are provided as indexes of the modes.

Book 7, on measured music, provides the raison d'être of the Speculum: the refutation of modern errors and the vindication of traditional authority, especially Franco ‘the German’ and ‘a certain one called Aristotle’ (Magister Lambertus). ‘Measured music’, began Jacobus, ‘is the harmonious joining of distinct notes, equal or unequal, performed simultaneously under some measurement of time.’ Since this always required at least two voices, he turned first to an account of discant, which he defined as ‘double song’, made by adding at least one part to a plainchant tenor. The relationship of the parts was governed by the perfect consonances and contrary motion, and added voices must consider their relation not only with the tenor but also with the other parts. He devoted a chapter to ‘inept discantors’, some of whom did not even know plainchant, while other more learned composers wrote beautiful but difficult discants, abandoning the example of the ancients.

In categories of discant composition he distinguished organum purum from those which are measured in all parts: hocket, copula and discant ‘simply performed’ comprising conductus, motets, fuge, cantilena and rondellus. He next turned to the time relationships of measured music. For the ancients the basic value was a brevis recta divisible into two unequal or three equal parts. The moderns also employed an imperfect brevis divisible into two equal parts, and they divided the three equal parts of the brevis recta into three smaller units each. These smaller note values imply a slowing in performance tempos apparent in Jacobus's remark that the Franconian semibrevis equalled the minim of the moderns. The division of the brevis into as many as seven semibreves is attributed to Petrus de Cruce, a division into as many as nine to ‘another’. (Jacobus ‘seems to remember’ having heard in Paris a triplum composed by Franco himself in which the brevis was divided into more than three semibreves.)

Rhythmic modes and note values are cited according to Franco. In addition to the longa, duplex longa, brevis and semibrevis of the ancients, the moderns employed the maxima and the minima and further complicated notation by such forms as a semiminim with tail and flag. Jacobus reluctantly proposed a lozenge tailed obliquely to indicate a major semibrevis, a simple lozenge to indicate a minor semibrevis. Considerable space is devoted to the point-by-point refutation of the nine ‘conclusions’ on imperfection of Johannes de Muris (CoussemakerS, iii, 109–13). Finally, the ancient and modern styles are compared as to perfection, subtlety, freedom and stability. In the course of this Jacobus cited the varying signs used by the moderns to indicate perfect and imperfect mode and time. In an epilogue he reviewed the lengthy progress of his work and prayed an entrance into the everlasting heavenly chorus of praise.



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