William of Malmesbury's position as cantor at Malmesbury received little attention in his brief autobiographical comments, and was consequently accorded little significance by later historians. However, the connection between the office of cantor and that of chronicler in the cases of several well-known English writers of the twelfth century has received increasing attention in recent years. As David Rollason has pointed out, Symeon of Durham's role of cantor or precentor (the terminology was variable) meant that he had overall responsibility for the monastic library, the scriptorium, and the complex arrangements associated with the recording and commemoration of the significant dead. A similar point applies to Eadmer of Canterbury, who moved from hagiography to historical writing after his own period of service as cantor. The position of the cantor in relation to historical writing in the monasteries of Anglo-Norman England may never have been as powerful as it was in continental Europe, as argued by Miriam Fassler. Nevertheless, she traces a shift in the role during the eleventh century – namely, that the cantor took over the role of armarius or librarian and had fewer responsibilities for the technical aspects of musical performance – which also affected English houses. William of Malmesbury's understanding of this role is currently being explored by Paul Hayward.
However, whereas scholarly attention has focused on the role of the cantor/armarius as custodian of books, liturgical observance and remembrance, this article will address a related, but distinct, aspect of the cantor's duties, namely, his need for expertise in computus, and the light this sheds on William's views on correct historical dating.
As cantor, William would have known that the timing of the monastic day was a highly technical matter closely tied to the timing and the cyclically varying details of the Opus Dei, based on the movements of the heavenly bodies. The ringing of the bells to signal the various canonical hours was a serious matter, which required the cantor's expert advice, since these hours were meant to be calculated on the basis that there should always be twelve hours between sunset and dawn and another twelve between dawn and sunset. The result was that the actual length of day and night hours varied constantly with the seasons, and that it was only at the equinoxes that all twenty-four hours were of the same length as one another.