William Durant the Younger was the author of two equally remarkable documents for the history of political thought: the paréage of Mende and the Tractatus Maior. But whereas he succeeded in putting into effect the ideas that he articulated in the former – succeeded, indeed, in laying down a constitutional regime that would survive intact for almost half a thousand years – he failed completely with the latter. What explains this spectacular success and this no less spectacular defeat? It is not that in the paréage he opted for princely sovereignty whereas in the Tractatus Maior he opted for republican government. Nor is it that the paréage dealt with a local territory whereas the Tractatus Maior dealt with the universal church. It is not even that the circumstances favoured his attempt to subject the nobility of the Gévaudan to his control, but did not favour his attempt to subject the papacy to the will of general councils. It is that he insisted on the authority of law.

There is a sense in which the authority of law is inseparably wedded to republican government, namely, the sense in which the law defines the common good and curbs the capricious will of arbitrary rulers.