“Kings needed help or counsel or money. They wanted assent to their policies and political support for them. These obvious facts should indeed receive due emphasis in any institutional history of the Middle Ages, but it is a delusion to suppose that, by merely calling attention to them, we are providing a sufficient explanation for the rise of medieval constitutionalism. The problem of maximizing assets to governmental policies arises for all rulers in all societies. It is not normally solved by the development of representative assemblies. Our argument is not that hard-headed medieval statesmen behaved in such-and-such a way because some theorist in a university had invented a theory saying that they ought to do so. The argument is rather that all men behave in certain ways in part at least because they adhere to certain ways of thinking. No doubt the ideas that are most influential in shaping actions are ones that the agent is hardly conscious of at all – he takes them so much for granted. But the historian has to make himself conscious of those ideas if he is to understand the men of a past age and the institutions that they created.”
Brian Tierney, “Medieval Canon Law and Western Constitutionalism,” in The Catholic Historical Review (Washington, April, 1966) excerpted in Bertie Wilkinson The Creation of Mediaeval Parliaments [and BTW Wilkinson was my grandfather].