Network Theory and the Reconstruction of Social Networks from Historical Sources

Dr Andrew P Roach,
Mr Paul Ormerod
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This interdisciplinary paper addresses the themes of transmission of knowledge and dynamics of communication.

In the last decade there has been important quantitative work on the mathematics of modern social networks, including the structure of the Internet and the transmission of sexual diseases. An important theoretical finding, supported by empirical evidence, has been that the ease of transmission across social networks varies dramatically according to the network's structure. The likelihood of any individual idea or piece of information percolating across a network is greatly enhanced in so-called 'scale free' networks. Conversely, different or disrupted networks can lead to isolation or a purely localised presence.

The implications of these developments for networks of the Past have not yet been fully explored. Detailed relevant data of the same quality as say, work on mapping the World Wide Web, is rarely available from historical documents, and even less so from before the Industrial Age. However, we can aim at a qualitative reconstruction of important networks in their historical context, by linking this theoretical work with what empirical evidence we have. From this we can gain new perspectives on how and why something disseminated widely or was contained. A prime example would be the spread of the Cathar heresy in western Europe between 1100 and 1400. The Catholic Church devised various strategies of containment which eventually took effect. However, the heresy persisted, often reviving, when seemingly on the verge of eradication. We obtain a better understanding of both phenomena from a study of network structure through which ideas were communicated in medieval Europe.

This paper would build on our previous research published in the leading statistical Physics journal, 'Physica A' (P. Ormerod & A.P. Roach, vol.339 (Aug. 2004), pp.645-52.

Keywords: Network Theory, Social Science, History of ideas, Transmission of Heresy and Inquisition
Stream: History, Historiography, Religion, Spirituality, Science, Environment and the Humanities
Presentation Type: Paper Presentation in English
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Dr Andrew P Roach

Lecturer in History, History Dept, University of Glasgow

I was born in Hull, England, and was a student in the 1980s, gaining my first degree from Cambridge, a Masters from Reading and a D.Phil from Oxford. My doctoral thesis was on the Cathar heresy in southern France and Italy and in particular the degree and method of communication between heretical communities in the two places. I have subsequently published articles on the 'goodwill economy' among heretics and believers, the origins of the Inquisition in penitential movements and the historiography of the Cathars as the embodiment of the Occitan spirit. I have just completed a book on 'The devil's World: heresy and society 1100-1300' to be published by Longman in Spring 2005. I worked as an economic analyst at the Henley Centre for Forecasting in the early 1990s where I met Paul Ormerod. We share an interest in the function of social networks, non-traditional economics and rugby league. we are currently working on how the study of historical networks of dissent may lead to a better understanding of international terrorism.

Mr Paul Ormerod

Director, Volterra Consulting

Read Economics at Cambridge, then took M.Phil. in economics and econometrics at Oxford. Worked as a conventional economic modeller and forecaster at the National Institute of Economic and Social Research, 1973-80. Became senior UK forecaster and modeller. Became Head of Economic Assessment Unit at the 'Economist' newspaper group, 1980-82. 1982-92 Director of Economics and Deputy MD of Henley Centre for Forecasting: helped build the Centre into successful commercial enterprise owned by the management team. Author of best-selling 'Death of Economics' (Faber,1994) and 'Butterfly Economics' (Faber, 1998). Visiting Professor of Economics, Universities of London and Manchester, 1983-97. More information on Paul and his work is available on

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