Every historian who gives the Wiles Lectures at The Queen's University of Belfast incurs many debts of gratitude. It is a pleasure to acknowledge some of mine. I would like to thank the Vice-Chancellor and Mrs Froggatt for their exceptionally kind hospitality. Professor W. L. Warren and the staff of the History Department helped in many ways to make my visit to Belfast a very pleasant experience. I am grateful to the National Endowment for the Humanities for a fellowship grant. Above all I must thank Mrs Janet Boyd, whose generosity has made the Wiles Lectures series possible, and the trustees of the Wiles endowment for their invitation to deliver the lectures in 1979.

The trustees also invite historians from other universities to attend the lectures. After each afternoon's talk the visitors join with interested local scholars to form a kind of seminar where the day's performance is criticized and discussed. To a medievalist it all seems very fitting. After the kctum comes the disputatio – often lively, sometimes strenuous, always joyous. I am grateful to my colleagues for all the friendly criticism that I received on these occasions.

One purpose of the Wiles Lectures is ‘to encourage the extension of historical thinking into the realm of general ideas’. The occasion tempts a historian to emerge from his specialist studies to address some broader theme. As will be evident, I succumbed to temptation. At our evening ‘seminars’ the questions that arose again and again concerned the methodological problems inherent in any such enterprise, the difficulties involved in an attempt to pursue the history of constitutional ideas over long periods of time.