On the new edition of Grosseteste’s Compotus

The medieval ecclesiastical calendar rested on the foundation of two interlocking calendrical cycles, which were represented by the Julian calendar, with its 28-year cycle of weekdays, and by a 19-year cycle of ‘epacts’ for tracking the phases of the Moon. Monks and clerics who sought to learn more about the scientific background of these cycles, or simply to familiarize themselves with their use, could do so by turning to books on the so-called computus, of which scores were produced in Latin Europe between the seventh and thirteenth centuries. During the twelfth century, this tradition of writing didactic treatises on calendrical astronomy was challenged by the new availability of translated Arabic, Hebrew, and Greek texts on mathematical astronomy, whose contents showed that the discipline of computus had relied on an overly simplistic account of celestial motions, which obscured the inadequacies inherent in the received cycles. As a consequence of these inadequacies, the Church frequently violated its own rule of always celebrating Easter Sunday on the first Sunday after the first full moon in spring.

            Calls to reform the ecclesiastical calendar by increasing its astronomical accuracy were first sounded in the 1100s and began to grow in volume during the following century, which saw the rise of the universities. The first medieval authors whose thoughts on the matter exerted a truly long-long and far-reaching influence was Robert Grosseteste, whose many scientific writings include a Compotus in twelve chapters (compotus being the common thirteenth-century spelling of computus). The work offered a fresh and reform-oriented perspective on a time-honoured discipline, in which traditional computistical doctrines were compared and confronted with information drawn from Graeco-Arabic astronomy. At the same time, it could be read as a fully-fledged textbook on the discipline, one that taught all the elements an aspiring cleric needed to master in order to understand how the existing calendar functioned. Its didactic streak is reflected most clearly by the frequent inclusion of mnemonic verses to summarize particular rules and principles, whereas other parts exhibit a greater tendency towards condensation and mathematical abstraction.

            Numerous medieval and even early modern scholars are known to have read, excerpted, or criticized Grosseteste’s Compotus, among them some famous names such as Roger Bacon, Campanus of Novara, Robert Holcot, and Pierre d’Ailly. The text began to fall into obsolescence only after 1582, when the introduction of the Gregorian calendar by the Roman Church did away with the defects Grosseteste and others had been complaining about. Grosseteste’s foray into calendrical astronomy was brought back from obscurity in 1926, when the British medievalist Robert Steele published the text in one of the volumes of his great edition of the Opera hactenus inedita of Roger Bacon. Although this edition has served virtually all scholars interested in the text until now, its shortcomings are readily apparent. Steele must have worked in great haste and consequently ignored most of the manuscript witnesses already known at the time, relying solely on two copies in the British Library. Next to the corruptions encountered in these manuscripts, his edition is marred by a great number of transcription errors, which in some cases alter the intended sense of the text.

            My interest in these textual problems was first sparked in 2015, when Giles Gasper kindly invited me to contribute to the Ordered Universe Project’s ongoing exploration of Robert Grosseteste’s scientific writings by translating the Compotus into English. In April 2016, I had the opportunity to present parts of an early draft of this translation at an Ordered Universe Symposium in Rome, a report on which can be found here. The act of rendering this text into a modern language brought the deficits of Steele’s edition more clearly to the surface and, as a consequence, strongly indicated that modern scholars would profit from a critical re-edition. Yet this was more easily hoped for than actually done. Ever since S. Harrison Thomson’s 1940 census of Grosseteste manuscripts, it had been known that the Compotus was extant in at least 29 different copies, which meant that a full critical edition of the text was going to be a very time-consuming task.

            Having concluded that I would not be able to take on this task on my own, I contacted Alfred Lohr, a German mathematician who since his retirement had been specializing in technically sophisticated editions of medieval computus texts, all of them produced with prodigious speed and efficiency. Alfred had just completed a major project on twelfth-century computus and was ready to set his sights on the major works of the thirteenth century. Luckily for our collaboration, he was willing to shelve parts of his larger project in order to re-focus his energies on Grosseteste.

            Together we raised the number of known textual witnesses to 38 manuscripts spread across collections in Europe and the United States. Of these, we eventually managed to access all but one, which remains in undisclosed private ownership. On the way towards selecting the best witnesses for the edition, Alfred transcribed c.2500 words from the beginning of the text for each of the available copies and used these transcriptions as the basis for creating a family tree or cladogram for all manuscripts. Drawing on his programming skills, Alfred generated the cladogram automatically from a software called PAUP*, which is otherwise used by biologists to reconstruct phylogenetic trees. After much fine-tuning, the resulting cladogram revealed that the surviving manuscripts of Grosseteste’s Compotus can be divided into two groups representing slightly different versions of the text. The version closest to Grosseteste’s original composition is only attested in a minority of witnesses, which all originated in England. Most other manuscripts, including those with a continental origin, present the text with a number of significant additions and modifications, which presumably were the work of later scribes. The cladogram helped us narrow the number of witnesses for the edition down to eleven, which were selected for being both close to the hypothetical archetype and representative of the different branches in the text’s transmission. Alfred proceeded to make a full collation of these eleven manuscripts and created a new critical text on their basis.

            The Compotus is not counted among the scientific opuscula that make up the core remit of the Ordered Universe Project and hence had to appear separately from these texts. At Giles Gasper’s recommendation, we eventually tried our luck with Oxford University Press, who in September 2017 offered us a contract. As promised in our initial book proposal, I equipped the volume with a detailed commentary on each chapter of the Compotus and an introduction that addresses some key issues concerning the text’s genre, authenticity, and reception. Most importantly, perhaps, the introduction argues that Grosseteste probably composed his Compotus in the early-to-mid 1220s and certainly no later than 1232. It also adduces evidence suggesting that Grosseteste wrote this text while studying in Paris, which aligns with the hypothesis that he spent an extended period prior to 1229 in France rather than England.

            The complete volume was published in March this year. It is our hope that it will supply scholars of medieval intellectual culture with new perspectives on the discipline of computus and Grosseteste’s role in its development.

C. Philipp E. Nothaft

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