Since the advent in the nineteenth century of systematic musicological inquiry, achieving a comprehensive grasp of the medieval theoretical entity known as the hexachord has proved elusive. While it is evident that this system of six-note pitch sets originated as a means to facilitate sight-singing, what further applicability it may have had to conceptions of tonality has remained an object of speculation. Particularly intransigent has been the problem of defining the relationship of hexachords to the octave-based system of ecclesiastical modes operative throughout the period from the ninth to the sixteenth century – and this despite commentary offered in myriad studies of widely varying scope and focus. Yet the possibility of arriving at a clearer picture of hexachords remains alluring, due to the potential ramifications it might entail for our understanding of both theory and practice.

Prior to the contribution of Gaston Allaire (1972),Footnote ¹ no book-length study had been devoted to the topic of hexachords. Subsequently Allaire's work was furthered by Christian Berger, whose 1992 Habilitationsschrift postulated a set of conditions obtaining in late medieval music – an interpretation that can only be characterised as radical.Footnote ² That study suggests, first, that hexachords comprised the primary conceptual apparatus of a tone system yoked to the ecclesiastical modes; and second, that the modes themselves assumed a priori compositional significance in polyphony as early as the fourteenth century. Although the scholarly reception of both authors' work has on the whole been sceptical,Footnote ³ no competing hypothesis of equal scope has hitherto been advanced. Despite the lack of any resulting consensus it is nevertheless true, as Mengozzi remarks, that the view of ‘ut–la syllables as an organizing principle of the medieval gamut’ (p. 24) has attained currency, to the point where it is reflected in standard music-history survey texts. In this sense his book offers a much-needed reassessment – a necessary step towards untangling the skein of issues surrounding the medieval hexachord. The fundamental question it seeks to answer is whether ‘medieval and Renaissance musicians … understood Guido's hexachord [as opposed to the octave] to be the primary diatonic “yardstick” of their musical space’ (p. 12).

Perhaps wisely, the author does not frame his inquiry strictly as a rebuttal of the Allaire–Berger school. Instead, he traces the intellectual history of hexachordal theory from its inception until the sixteenth century, periodically invoking opinions of latter-day authorities such as Walter Wiora, Richard L. Crocker and Margaret Bent. Throughout, the semi-mythical figure of Guido d'Arezzo assumes a position of central importance, with the topical focus being the reception of (putative) Guidonian theory. (It is curious, however, considering the study's overriding theme, that the term ‘hexachord’ is not specifically reflected in its title.)Footnote ⁴ Apart from the introduction there are no references to actual musical examples. The intent is rather to demonstrate how ‘a closer look at the documentary evidence and at the reception history of the hexachordal system points to a broad range of positions on the problem of medieval and Renaissance diatonicism’ (p. 11). In this connection, Mengozzi postulates two interpretative possibilities: first, a ‘strong’ view of hexachords (which he claims currently prevails) as being ‘syntactically more significant’ than the octave, against which he opposes a second, ‘soft’ mode of apprehension, wherein ‘the structural significance of the ‘Guidonian hexachord’ was relative rather than absolute, and circumscribed rather than boundless’ (pp. 11–12).

The book is divided into two sections, each of four chapters. Part I, entitled ‘Guidonian Solmization in Theory and Practice’, attempts to clarify, through examination of carefully deployed primary sources, how the hexachordal system developed in the two centuries following its invention. Here the author argues that ‘unlike the church modes, the hexachordal set was not designed to function as a background scale’. Instead, its purpose was ‘foremost pedagogical and mnemonic, rather than theoretical or foundational’ (p. 33). This view is consistent with a practical concern, paramount in the teaching of sight-singing to neophytes, which in the reviewer's opinion was a chief motivation for the hexachord's invention, namely that the three hexachordal sets on C, G and F respectively (the latter invoking the pitch B flat) represent those loci within the gamut upon which the largest diatonic interval possible (major sixth) can be spanned without invoking a second semitone. The pedagogical utility of this construct is compellingly secured by the invariable medial position of the half-step (i.e., T-T-S-T-T). And it was precisely this attribute that allowed the hexachord subsequently to take on an additional function as modal signpost, ‘a portion of diatonic space that is shared by the eight modal categories and is thus sufficient for a prima facie recognition of those categories’ (p. 38).

According to the author, it was towards the end of this formative period, in the era of scholasticism, that a crucial alteration in the meaning of hexachordal syllables becomes discernible:

Part II (‘Reforming the Music Curriculum in the Age of Humanism’) traces further stages in this semiotic transformation. The focus here is upon how humanistic ideologies played a role in shaping the Renaissance's reception of Guido d'Arezzo, with consequent effects upon the status (and stature) of hexachords in music theory. Thus, notwithstanding certain individuals such as Johannes Ciconia (d. 1412) who articulated didactic methods that sidestepped Guidonian tradition, ‘far more successful was the counterargument that several late fifteenth-century theorists mounted in defense of the hexachordal system. Its centerpiece was the thesis that with his syllables Guido had … in fact changed the very structure of the diatonic system by substituting the old tetrachordum of the Greeks with his new hexachordum’ (p. 113).

Ultimately, according to Mengozzi, this classicising view of Guido prevailed in the writings of Gallicus (Chapter 6), Gafori and Burtius (Chapter 7), and Zarlino (Chapter 8). In expounding the contributions of these various individuals, Mengozzi delineates many points of convergence, but also enters into their considerable disparities and disagreements (in particular the morass of polemic surrounding the figure of Ramos da Pareja), as well as elucidating the subtle propagandistic ends to which humanistic music theory was subject.

The author's writing style is basically clear, with occasional infelicities (e.g. p. 152, ‘expedite’ – presumably ‘expeditious’), and some tendency towards colloquial usage. The many excerpts from treatises of the period (including numerous facsimiles) are judiciously handled. From a rhetorical standpoint, however, the book tends to be rather repetitive of its basic arguments, and could probably have been streamlined somewhat in that regard. There are occasional factual errors, as in the contention regarding ancient Greek theory that ‘each tetrachord was truly conjunct to the immediately lower one within the Greater Perfect System’ (p. 205).Footnote ⁵ Moreover, the very structure of Mengozzi's narrative, amplified in a closing pronouncement that ‘modernity has often had more reasons to embrace the foundational image of Guido that it received from the hands of prominent authors such as Gafori and Zarlino, than to reject it’ (p. 256) might be taken to imply that musicological viewpoints positing an essential role for hexachords within the tone system(s) of early music stem from late-Renaissance treatises. Yet scholarly debate, as it has been framed over the past 150 years, has not proceeded primarily from consideration of those texts. On the contrary, the seminal modern contributions have tended to focus on the earlier phases of hexachordal theory.Footnote ⁶ This observation is not intended to detract from the substance of the author's argument but only to point out that the book does not constitute a thoroughgoing examination of pertinent modern scholarship.

In sum, this monograph sets forth a well-nuanced case that structural models of pitch in early music were fundamentally grounded in an octave-based, heptachordal and not hexachordal, framework. In pursuing his arguments, the author sketches out a series of intellectual/cultural contexts within which various theorists were active (although further work clearly awaits in that arena). These excursus serve to unfold the story in some measure of hermeneutical fullness. In refuting the idea that medieval musicians necessarily associated hexachords with properties of tonality, the book fills an important niche in the historiography of early music, and its essential thesis may well find general acceptance.