This important publication increases the accessibility of a less-well-known medieval treatise on music theory devoted to the Gregorian chant repertoire for Mass and Office. The Tractatus de tonis by Guy de Saint-Denis, written in the first decades of the fourteenth century, consists of two distinct parts: (1) a discursive treatment of various musical topics that is heavily dependent both on the writings of earlier music theorists and on those of the philosopher Pierre d'Auvergne, and (2) a "didactic" tonary that catalogues (with some commentary) representative chants in each tone (mode). In a tonary chants for the Office are classified by the differentia (psalm-tone cadence) appropriate to the melodic shape of various chant incipits.
Guy's Tractatus was not included in the classic anthologies of Martin Gerbert (Scriptores de musica sacra, 1784) or Edmond de Coussemaker (Scriptorum de musica nova series, 1864-76), nor among the treatises published in the series Corpus Scriptorum de Musica (1950ff.). It did, however, benefit from an exemplary edition accompanied by an introductory volume of "Studien" by Sieglinde van de Klundert (spelled "van der Klundert" in the present edition).  Her analyses probed the sources used by Guy, the teaching of the treatise, its philosophical treatment of ethos and affect, and the liturgy of the Parisian abbey of Saint-Denis. Van de Klundert also supplied a facsimile of the tonary from the unique source of the treatise: London, British Library, MS Harley 281 (early fourteenth century), a compilation supervised by Guy that includes treatises by Guido d'Arezzo, Johannes de Grocheio, Petrus de Cruce, and the pseudo-Oddonic Dialogus de musica, in addition to the Tractatus de tonis itself. The translators speculate that Guy, "a scholarly monk who loved the liturgy of his abbey" (xxxiv), might be the same as Guy de Châtres, who rose to the rank of abbot of Saint-Denis (1326-1343).
This welcome new edition and English translation of the Tractatus by a team of Australian scholars introduces the treatise by identifying the sources of Guy's teaching, sketching the history of his abbey in the late thirteenth and early fourteenth centuries, and exploring the treatise's relationship to the Cistercian and Dominican chant traditions.  There is also a detailed index of the treatise (xxxvii-xlii) based on the numbering of its sections assigned by the editorial team, a lexicon of terms appearing in the treatise, a brief glossary, a bibliography of primary sources, and a selection of secondary source material ("Flueler" should be "Flüeler"). Also supplied is a complete list of chants mentioned in part 1 of the treatise and those notated in the tonary with concordances to relevant sources. At the bottoms of pages the reader will find the incipits of chants mentioned but not notated in the treatise, a service that enhances the value of this new edition.
The translators have done an excellent job in rendering Guy's occasionally overelaborate prose style into readable English, and they justify the slight liberties they have taken to facilitate the reader's access to the text (xxxvi). One might quibble with a few translation choices, however. In 1.4.8 "strengthen" might fit the context better than "comfort" as a translation of "confortat" (cf. Philippians 4:13), and one might be inclined to prefer "odd" as the translation for impares (as applied to the numbers 1, 3, 5, and 7) over the edition's "uneven" (1.2.10). Boethius' comment (De institutione musica 1.1) about the performance medium appropriate to "chaste and modest music" might be clearer if simplicioribus organis had been rendered as "simpler musical instruments" rather than "organs." A minor slip has allowed "post-communion" (a prayer said by the priest) to be identified as the communion chant of the Mass (xii).
Nearly all of the first part of the treatise is derived from earlier authors, as can be verified by a glance at the 268 footnotes in which the translators have not only identified the sources but also provided the complete Latin texts. Guy relies heavily on Boethius, not only for his narrative about the mythological origins of music but also for his teaching on the proportions of musical intervals, in which he distinguishes between simultaneously sounding pitches (concordantie) and successive pitches (concordie). He pays tribute to Guido d'Arezzo by frequently quoting his authoritative teaching, and he also borrows extensively from Johannes Grocheio's De musica (ca. 1300), even referring to some of the celebrated passages in which Grocheio evokes the secular music making of his day in Paris. The Harley manuscript with the Tractatus is one of the two sources of Grocheio's treatise, and it is conceivable that these two Parisian authors might have known each other. In addition, Guy had at his disposal what he called a libellus antiquus on music, but he was unaware of the identity of its author.
A curious presence among Guy's auctoritates is Pierre d'Auvergne (d. 1304), not a music theorist but a philosopher and theologian of the University of Paris, who became bishop of Clermont. Guy drew on Pierre's commentary on Book 8 of Aristotle's Politics, a continuation of Thomas Aquinas's unfinished commentary on that work. Guy was likewise aware of Pierre's responses to two questions about music's ability to arouse the passions and to promote virtue, respectively, that were presented at his final Quodlibetal at the University in 1301. Guy drew selectively from Pierre's responses, eschewing the physiological reflections that are so prominent in them.  At the end of the Tractatus de Tonis Guy credits Boethius and Guido by name, but not the "certain others" from whom he drew material.
On several occasions Guy inserts himself into the discourse, expressing personal opinions about something or confessing that he does not know the reason for this or that. For example, he voices a dislike for new offices in which chants (antiphons and responsories) were composed in ascending modal order: 1 to 8. Such rigidity could potentially hinder adapting the melodies to "the material [i.e., words] on which they were founded" (1.4.22). For this view he summons the authority of Guido d'Arezzo (Micrologus 15: in tristibus rebus graves sint neumae, in tranquillis iocundae, in prosperis exultantes). Guy was convinced, furthermore, that each tone had a special ethos: tones 1 and 4 "disposed to virtue." He defended chants thought to be "irregular", ostensibly because they transcended the theoretical ambitus of their tone (mode). He argued that, despite that fact, it was still possible to delight in "the sweetness of their modulations" (1.3.20).
Towards the end of part 1 of the Tractatus Guy introduces a consideration of "what sort of musical harmonies or consonances are able to cause or excite which or what sort of passions of the soul in hearers" (1.4.15). As is clear from the footnotes, most of this section paraphrases material from Pierre d'Auvergne's commentary on the Politics and his musical quodlibetals of 1301. According to Guy, in a state of rapture (the focal point of one of Pierre's questiones) "the soul draws back and recalls the spirit . . . from externals to internals" (1.4.15). The use of the definite article with "spirit" throughout the translation of this section presents an interpretive problem. In ancient and medieval physiology "spirit" referred to a subtle vapor believed to be transported through the veins, arteries, and nerves of the human body. It was not "spiritual" in the sense of being immaterial. Three kinds of spirits were distinguished: (1) natural, originating in the liver and carried throughout the body by the veins, (2) vital, originating in the heart and carried by the arteries along with a small amount of blood, and (3) psychic (also called "animal" from anima), thought to originate in the ventricles at the base of the brain by refinement of vital spirit and then transmitted through the (supposedly hollow) nerves. In the condition of rapture spirit retreats ad interiora, thereby rendering the subject immobile. Reading spirit without "the" conveys a more accurate understanding of what Pierre (and presumably Guy) had in mind. 
The production quality of the paperback version sent for review is very high. The press and the translators have negotiated the many challenges of aligning the Latin and English texts and of inserting the extra musical examples as "footnotes" to the translation.
1. Guido von Saint-Denis, Tractatus de tonis: Edition und Studien, 2 vols. (Bubenreuth: Hurricane Publishers, 1998).
2. Three of the translators published a study of the abbey's chant in Plainsong and Medieval music 23 (2014): 151-176. The bibliography's reference to "Journal of" before the title of the serial should be omitted.
3. While the present edition was in progress, a translation of Pierre's questiones and a commentary on them was published by the present reviewer: "Music, Passion, and Virtue in Two Quodlibetal Questions of the Philosopher Pierre d'Auvergne," Philomusica on-line 15/2 (2016): 1-54. This is available at: .
4. For further elaboration see the publication mentioned in the previous footnote.