The Medieval Review 11.02.19

Verbist, Peter. Duelling with the Past, Medieval Authors and the Problem of the Christian Era (c. 990-1135). Studies in the Early Middle Ages, SEM 21. Turnhout: Brepols, 2010. Pp. x, 366. 70.00 EUR ISBN 978-2-503-52073-5. .

Reviewed by:

David Defries

Peter Verbist's book analyzes the corrections that eight medieval scholars--Heriger of Lobbes (d. 1007), Abbo of Fleury (d. 1004), Marianus Scottus (d. 1082), Gerland the Computist (d. post 1093), Sigebert of Gembloux (d. 1112), Hezelo of Cluny (d. 1123), an anonymous author from Limoges and Heimo of Bamberg (d. 1139)--made to Dionysius Exiguus's (d. ca. 540) chronological system based on the supposed date of Christ's incarnation. Verbist, the librarian of the Faculty of the Arts at the Catholic University of Leuven, states that he had two major goals in composing his text. First, he wanted to provide a comprehensive technical analysis of each author's corrections. According to Verbist, previous studies were either based on defective editions of the relevant texts, only survey portions of an author's oeuvre or, in the cases of Hezelo and the anonymous author (whose text Verbist unearthed in the holdings of the Bibliothèque nationale de France), do not exist. Second, he claimed to show that these medieval scholars furthered western intellectual autonomy and individualism before the rise of Scholasticism by challenging authoritative traditions. Verbist's painstaking reconstruction of the logic behind each correction accomplishes his first goal in spades. The parts of the text devoted to the second goal are, however, less successful. They suggest that the corrections merit a separate study of their place in the intellectual development of the medieval West. As a result, Duelling with the past will likely be most interesting to specialists in medieval computistics, though the book will also reward scholars who work on medieval theology, philosophy and historiography with many important insights into how medieval scholars used time as a concept in pragmatic applications.

Computistics was the medieval discipline devoted to the calculation of dates--most importantly the date of Easter. Because it married astronomy and mathematics with theology and scriptural exegesis, it was fiendishly complicated. Based on the Gospel accounts of Jesus' death and resurrection, Christians associated Easter with the Jewish Passover, which they believed should be celebrated on the first full moon after the spring equinox (the point in the spring at which the lengths of the day and the night are roughly equal). In 46 BC, the creators of the Julian calendar fixed the date of this equinox at 25 March. Because the solar year is 365.2422 days long, however, by 325, when the Council of Nicaea met, the equinox actually fell on 21 March, meaning that the calendar date of the equinox was out-of-sync with the natural phenomenon. Predicting the first full moon after the equinox is similarly fraught with difficulties because a lunar month or lunation (the time from one full moon to the next) is 29.5306 days. For symbolic reasons, most Christians also moved the celebration of Easter to the nearest Sunday after the full moon. These facts led to varying approximations and adjustments in constructing lunar and solar calendars, and thus, disagreements about how to synchronize the calendars to reckon the dates of previous and future Easters. Scholars constructed cyclical patterns based on varying factors to predict when certain combinations of lunar and solar data would repeat. For example, a 532-year cycle takes the 19 years necessary to fit a whole number of lunar months into a whole number of solar years, multiplies this by 7 (the number of days in the week) then multiplies this by 4 (the number of years in a cycle that uses leap years to adjust the solar calendar). When scholars turned to the scriptures for other chronological information that might help in their calculations--the length of Jesus' public career, the date of his death, the date of his incarnation--they found imprecise and conflicting traditions, leading them to differing interpretations. The differences were significant. For example, Eusebius of Caesarea used the Septuagint text of the Hebrew scriptures and dated the birth of Christ to 5199 years after the creation of the world, while Bede used the Masoretic text to date it to 3952 years after the creation. Their respective dates for the impending apocalypse would then differ by thousands of years. Verbist provides a succinct narrative for the development of the most important computistical traditions in his introduction, but non-specialists will probably need to supplement it with other texts, such as the ones from which this paragraph has been cribbed--the introduction to Faith Wallis's Bede: The Reckoning of Time (1999) and Deborah Deliyannis's contribution to Time in the medieval world (2001)--as well as Georges Declercq's Anno Domini: The Origins of the Christian Era (2000).

Eventually, with the help of Bede's computistical texts, the monk Dionysius Exiguus's dating system and Easter calculations became dominant in the Latin West, where all of the authors discussed in this book worked. Dionysius based his Easter table (a chart of calculations for the dates of future Easters) on a 95-year cycle that, for symbolic reasons, numbered years in reference to Christ's incarnation rather than to the first regnal year of the pagan emperor Diocletian, which had been used before. There was, however, a problem with Dionysius's table: as Bede alluded to in chapter 47 of his De temporum ratione, when one looks at Dionysius's table in the year designated for Christ's death, Easter does not fall on its traditional date. Bede used irony in his allusion to this discrepancy in order to mute his criticism of a system he ultimately wanted to promote. Verbist refers to the statement rather cryptically as Bede's "ironic formulation," which he says attracted much attention from later scholars (13).

After the introduction, Verbist plows right into his technical analyses of the eight known medieval attempts to correct Dionysius's calculations. As the proportions of the text and footnotes devoted to these analyses reveal, this is the heart of the book. Because each chapter deals with a single author's corrections in exhaustive detail and is mostly independent of the other chapters, it is impossible to do them justice in short summaries here. Fortunately, in the conclusion to the book, Verbist offers a brief set of summary observations that provide a taste of his analyses' contents. He notes that the critical element in each author's correction was a recalculation of the date of Christ's death. Six of the authors adopted the Latin tradition and five of these (Abbo, Marianus, Sigebert, Hezelo and the anonymous author from Limoges) dated Christ's death to the 12th year of Dionysius's incarnation era (12 AD). The other, Heimo, dated Christ's death to 1 AD. Heriger and Gerland both adopted the Greek tradition and dated Christ's death to 42 AD. Each author then tried to work out Christ's age at his death and then calculate back to the date of his birth. Those who placed his death in 12 AD calculated back to 21 or 22 BC, while those who placed his death in 42 AD calculated back to 8 or 9 AD. Heimo calculated back to 33 BC from 1 AD. Four of the authors tried to connect their dates to the date of Creation in a 532-year cycle of lunar and solar combinations, though each used a different method. Abbo failed to make the connection, while Marianus, Sigebert and Heimo succeeded in finding acceptable synchronicities. Finally, as Verbist observes, "with the exception of Hezelo and the anonymous author of Limoges, not a single correction is identical to another" (344).

In a series of sections at the end of the chapters and in the conclusion, Verbist discusses what the authors' corrections tell us about the intellectual development of the West. Each element of a computistical calculation usually had multiple authoritative traditions associated with it. As a result, each author had to choose which traditions fit the logic of his formulas. Verbist frames these choices as a dialectic involving authority and reason. He notes that authors were bound to respect authorities, but, at the same time, "they relied upon the rationality of medieval chronology," which was independent of tradition (348). This produced a tension that authors tried to relieve with various strategies. Sometimes they ignored contradictory traditions. Other times they acknowledged them but chose not to produce counter-arguments. Still other times, they countered authoritative traditions with other authoritative traditions. Finally, some offered refutations. Ultimately, Verbist argues, authority and reason proved complementary forms of knowledge, and by arguing according to the rationality of medieval chronology, the eight authors were striking blows for intellectual autonomy and individualism. Surely, this is too simplistic a formulation. Medieval intellectuals had long found meaning both in events recorded in the scriptures and in observed events according to a four-fold hermeneutic. One level of the hermeneutic was literal, while the remaining three were allegorical. As Galileo discovered to his chagrin, the literal interpretations could conflict with allegorical ones, but scholars often thought more in terms of which meaning took precedence. Computistical calculations did involve an element of empiricism, but this does not mean that scholars rejected inaccurate traditions. After all, God could miraculously alter the functions of the sun or moon to suit his purpose, and exegetes had long remarked on portions of the scriptures that were too troubling to interpret literally. Verbist's careful attention to the logic and accuracy of the corrections seems to have limited his field of vision. I would welcome a second volume on these authors from Verbist, in which he uses his considerable expertise in computistics to integrate each author's corrections into the wider corpus of his texts. Abbo of Fleury and Sigebert of Gembloux, for example, were prolific authors. Such a study would probably produce a more accurate view of each intellectual's approach to the relationship between authoritative interpretations and empiricist reasoning. Verbist's book indicates the critical points that will need to be explored more than it argues the points.

As a final comment on this enlightening book, I would add that Verbist misses opportunities to make his text more accessible to non- specialists. Perhaps because he is so immersed in the field, he often adopts technical terms without the accompanying short definitions that might allow the uninitiated to follow along. He defines, for example, the Passover, but not chronology or chronography. This should not, however, deter non-specialists from delving into the book.