Historians of economic and social change in the Middle Ages have developed explanatory frameworks spanning several centuries. These models depend on the gradually altering balance between the number of consumers and the resources available to meet their demands or the slow tightening and loosening of landlords’ ties over the peasantry. The problem with such long-term analysis is that the available evidence comes from much more limited time periods. For the agrarian economy, series of manorial accounts or court rolls are usually patchy and at best stretch for a few decades. The problem is particularly acute for the agrarian history of the century after the Black Death when manorial demesnes were increasingly leased out, meaning that fewer highly informative accounts were produced. One type of evidence, however, produces much longer series of indicators than the others: tithe.

By the fourteenth century religious corporations had often appropriated more than one parish from which they were owed tithe and, unable or unwilling to collect the grain themselves, the practice of selling tithes for cash became widespread. On the basis that tithe was supposed to represent one tenth of total output, French historians of the 1960s and 1970s developed methods for using cash tithe receipts as indicators of production levels. Up to now, this approach has not been used by historians of England but the resources here are abundant. In particular, the Durham Priory accounting material contains around 6,000 tithe receipts for the period 1349–1450 alone. These were collected and a technique developed for indexing and deflating receipts by price in order to convert them into approximations of arable output. The results of these calculations are shown in figure 12.1.

This unique series of indicators affords the historian an unprecedented opportunity to examine the detailed chronology of agrarian change over this period. However, despite the unusually large number of individual figures which make up the series, the tithe evidence must be treated with caution. In particular, the series makes no allowance for changes in tithe collection costs or the profits made by the tithe purchasers. The data for these factors are insufficiently consistent to enable them to be incorporated in the calculations.