The Measure of Multitude: Population in Medieval Thought (review)

This is a book about medieval ideas about demography, but with a question mark. Was there such a thing or, more to the point, what were the contexts, formulations, and implications of medieval speculation concerning human population? No one is more aware than Peter Biller of the dangers of anachronism in explaining the historical antecedents of current preoccupations. The Measure of Multitude is an exploration of a specifically medieval thought world, one elucidated in terms of medieval terminology and patterns, but forming a set of opinions about what we would call birth rate, population growth, sex ratio, and historical demography. Sources include medical treatises, but also canon law, theology, travel accounts, commentaries on Aristotle, and cartography.

The Middle Ages experienced both overpopulation (in relation to available land and technology) and periods of severe population decline. The book stops at 1340, thus before the Black Death of 1348–49, so that it describes opinions in an era that was, despite its high morbidity, aware of its own and others’ dynamic growth. Scholars in the twelfth to fourteenth centuries considered the consequence of immense and teeming population, especially with regard to the frighteningly expansive European cities and the apprehension that non-Christians were many times even more numerous than Christians in a vast but crowded earth.

Author of important studies of medieval theology, Peter Biller has combined an extensive and dazzling array of materials from intellectual, social, and medical writings to form a brilliant and intriguing work. He is generous in acknowledging debts to the historian John Baldwin for explicating the social theories of the Schoolmen, to the medical historians Michael McVaugh and Nancy Siraisi for the sociology of medieval medical practitioners, and to Richard Smith for reorienting the field of historical demography, but The Measure of Multitude is unique in its richness and effortless mastery of so many different methodologies.

The study of quantitative thought in the Middle Ages has received attention recently, notably in Joel Kaye’s Economy and Nature in the Fourteenth Century: Money, Market Exchange, and the Emergence of Scientific Thought (Cambridge University Press, 1998), which explores the relation between economic and scientific thought in terms of concepts, such as probability, dynamic equilibrium, and techniques of measurement. The Measure of Multitude reflects this attention to the quantitative mind set in investigating medieval discussion of such things as life-span and population density, but Biller is not as concerned as Kaye with pinpointing a supposed origin for modern scientific thinking. Rather he is interested in looking at how medieval intellectuals thought about factors affecting population. Measurement is obviously involved (as the title clearly implies), but so are prescriptive, nonquantitative ideas derived from theology and law. Thus the bishop of Paris and theologian William of Auvergne expatiated on marriage in quantitative terms of population statistics and estimates for his diocese. He also considered polygamy and (in a nonstatistical fashion) its possible effects on fertility (important in connection with crusade concerns about the vast number of Muslim enemies). William of Auvergne also wondered about the supposed low sexual drive of fat people (a notion derived not only from personal experience as a confessor, but also from Aristotle and Avicenna on animals). Curiosity and speculative daring were not necessarily always linked to what we would consider progress toward modern quantitative science.

To reconstruct medieval approaches to demography requires scholarship that crosses over barriers separating social and intellectual history. Biller is exemplary in this regard, so that, for instance, in considering birth control he extends the insights and resolves the limitations of the French social historian Georges Duby (who did not make use of Christian penitentials), and the legal historian John Noonan (whose account of contraception did not analyze the data from estate surveys). As I have indicated, Biller knows the social and theological sources...