De parte operativa (“On the operative part [of medicine]”) is the name traditionally given to an incongruous medical text, or pastiche of texts, by the Catalan physician Arnau de Vilanova (ca.1240-1311). Fernando Salmón Muñiz and Michael McVaugh edited this work as volume 8 of the Arnaldi de Villanova Opera Medica Omnia (AVOMO). This year, 2025, marks the fiftieth anniversary of the founding of AVOMO by Luis García Ballester, Juan A. Paniagua, and Michael R. McVaugh in 1975. AVOMO is one of the greatest editorial accomplishments of modern medieval studies, an admirable model of “slow scholarship” and a testament to the massive literary output and scholarly influence of Arnau de Vilanova. Because the numbering of volumes in AVOMO was planned decades in advance of completion, they have understandably been published out of order. Volume 8, De parte operativa (hereafter DPO), was published after most of the volumes 9-17. Salmón and McVaugh explain the key reasons for this delay: the series editors were not convinced in the 1970s that DPO was a genuine Arnaldian work, nor did they know of any medieval manuscript copies. The work had been known only from two sixteenth-century editions of Arnau’s opera (1504 and 1585), which print essentially the same text. In the intervening decades, Salmón discovered a manuscript source (Munich, CLM 7576) and a scholarly consensus was reached that it was indeed an authentic Arnaldian treatise, or rather, a selection of treatises in draft.

DPO is one of the more curious contributions to AVOMO and the editors emphasize their difficulties in making sense of the text, which they describe as “disjointed...almost as if there were three or even four different treatises included helter-skelter” (185). The work they edit is likely a collection of Arnau’s notes and draft treatises, later copied as a single work into CLM 7576. The editors use the title Pars operativa to refer to the core work of DPO, and define four separate parts of DPO, distinctions that do not appear in the earlier editions: 1) De fine medicine, an introductory paragraph on the purpose of medicine; 2) Pars1 of the Pars operativa, on the physiology of illnesses of the brain and mind; 3) Pars2 of the Pars operativa, on the diagnosis of mental illnesses, with their symptoms and treatments; and 4) a short additional text, Dolor stomachi, a series of aphoristic statements on the causes of stomach pain. The editors argue (228-229) that both the first and last elements were likely notes or parts of separate treatises, but because they have been read together with the Pars operativa for five centuries, they are kept together here.

Like most AVOMO volumes, this one includes a critical edition of the Latin text (105-175), supported by a brief discussion of editorial procedures (97-104), along with a preface and detailed introduction in both Catalan (9-94) and English (177-256). These are followed by a bibliography and two indices. The introduction is divided into seven sections, covering the DPO’s origin and structure, analyses of its four parts, a discussion of the Pars operativa’s relation to the Speculum medicine (edited by McVaugh as AVOMO 13), and a rumination on “Arnau’s vision of operative medicine--and its limits.” Reading the editorial introduction is essential to understanding the Latin text, as the editors lay out their impressive detective work in untangling the relationship among the separate texts in DPO and positing a theory of how they ended up together in manuscript and print. They tentatively suggest that both CLM 7576 and the 1504 edition are based on a single manuscript, now lost, in whichPars operativa and Dolor stomachi had been copied continuously and treated as a single text. This suggestion leads the editors to a “tantalizing speculation” (187) that this lost manuscript was based on Arnau’s papers and unfinished treatises found at Montpellier after his death.

McVaugh and Salmón argue that Arnau drafted Pars operativa in Montpellier in 1308-9 and abandoned it there when he went to Sicily, where he died in 1311. Arnau apparently intended Pars operativa to be paired with his monumental Speculum Medicine, finished around 1308, the Speculum covering the theoretical foundations of medicine and Pars operativa outlining the practical or “operative” part of medicine. With these two works Arnau aimed to provide a complete commentary on the tripartite Arabic-Galenic taxonomy of medicine--naturals (humoral physiology), non-naturals (external determinants of health), and contra-naturals (diseases, signs, and causes)--as summarized in the Isagoge of Johannitius (Hunayn ibn Ishaq, 809-873 CE) and elaborated extensively afterwards by Islamicate and European medical scholars. In the Speculum Arnau provided an extensive commentary on the naturals and non-naturals, and in the Pars operativa he began to discourse on the contra-naturals. The editors warn, however, against finding a coherent medical system in Pars operativa: it is a draft, both rushed and experimental, from a busy and stressful period of Arnau’s life.

In preparing the Latin text, the editors follow the CLM manuscript (C), emended as necessary from the 1504 Lyons edition (D), with reference to alternate readings in the 1585 Basel edition (E). The lines of text are numbered separately on each page and the columns and foliation of the CLM manuscript are indicated in the margins. They standardize the spelling throughout, opting for classical norms for routine words but using the most common medieval spellings from the witnesses for technical medical and pharmacological terms. They posit that DPO is “a kind of stream-of-thought draft...a product of ‘unthinking haste’” (102) and, as such, is full of digressions and grammatical inconsistencies that they do not try to correct. The editors have added throughout the text, as a valuable aid to readers, Latin titles in angle brackets, with Arabic numerals for the four component texts of DPO, letters A and B for the two partes of Pars operativa, and Roman numerals for the chapters (as they could best identify them) of those partes, such as “<I. De dolore capitis sive cephalea>” (118) and “<II. De frenesi>” (126). This editorial policy does impose a coherence on the text that is lacking in the manuscript itself, but the editors make a convincing case that this is the organization Arnau intended.

The only portion of the Pars operativa that Arnau completed was on the head, brain, and mind, and it serves, without reference to its source, as an extended commentary on Book III fen 1 of Avicenna’s Canon of Medicine, on the special pathologies of the head. This is surprising for Arnau, who was openly critical of Avicenna and his Latin followers and rarely cited the Canon in his earlier works. But it seems that in his later years Arnau grew more receptive to Avicennan ideas, which permeate the Speculum medicine and DPO. For this reason, the editors dedicate much of their introduction to tracking Arnau’s close reading of the Canon III.1, his adaptation of Avicennan ideas, and those instances where Arnau departs from Avicenna’s ideas about the brain’s morphology and the terminology and categories of mental illness. Of greatest interest in this last category is Arnau’s original formalization, based on occasional comments by Avicenna, of alienatio as a coherent classification of illness, especially of mental illness. Alienatio is the third and most serious corruption of the mental faculties (imagination, reasoning, and memory), following ablatio and diminutio. Arnau uses the term to apply to the complete loss of self, as occasioned by serious injuries to the mind, such as fatuitas, vesania, and deliratio.

In Pars1 of Pars operativa, Arnau defines injuries (nocumenta) to members of the body before proceeding to an outline of the nocumenta specific to the brain and the signs by which they can be diagnosed. In doing so, Arnau groups together conditions that we would now separate between physical injuries and mental illnesses. These include injuries to the senses, especially sight; injuries to cognition and behavior, with a focus on alienatio; and injuries to voluntary motion, marked by paralysis or spasms. Pars1 concludes with a catalogue of diagnostic signs indicating “injuries to the natural operations of the brain” (115) in the usual head-to-toe order, with a focus on the parts of the head (hair, ears, eyes, nose, tongue, face, neck), followed by a briefer outline of the lower parts of the body that enjoy a certain colligantia (link) with head: chest, stomach, intestines, womb, hemorrhoids.

Pars2 of Pars operativa is much longer (118-172)than Pars1 and will be more familiar to scholars of medieval medicine, as Arnau organizes it like the manuals of practica common to European physicians trained in the Salernitan mode after the twelfth century: it is a catalogue of pains, conditions, and diseases, each of which is defined by its signs and humoral causes, followed by a detailed regimen for prevention and cure. These conditions include headache, frenzy, lethargy, water on the brain, restless sleep, excessive drowsiness (somniculositas), sudden waking or insomnia, injury to understanding, vertigo, and night terrors. As in Pars1,Arnau is most concerned with the large class of mental illnesses he calls alienatio, and he dedicates nearly half of Pars2 solely to his eighth category De lesione cognitionis. What is more, this section on understanding and its loss includes two lengthy asides, which the editors have marked off with bold double brackets, one on how the bodily spirits can be altered in their nature and the other on the definition of stupor.

This edition and the learned commentary provide a wealth of fascinating information on the physiology, nomenclature, diagnosis, and treatment of mental illness in later medieval Europe. The editors describe a mature Arnau of Vilanova, writing after decades of medical teaching and practice, in the process of crafting a new and comprehensive approach towards treating pathologies of the brain within a system of “operative” medicine informed by theories of humoral complexion. The DPO is a difficult and complex text, due both to its nature as an incomplete draft and to the ambitious novelty of Arnau’s thoughts about the brain and mental illness. Moreover, the edition itself is intended for scholars already familiar with Arnau’s other medical treatises, as the editors couch their discussion of DPO in detailed comparisons to the earlier, completed treatises Speculum medicine and Repetitio super aphorismo Hippocratis “Vita brevis” (AVOMO XIV). McVaugh and Salmón have done justice to this complexity by their careful edition of the text(s) and their lengthy and meditative introduction, informed by decades of research into Arnau’s medical thought.