The Defender of the Peace

A long treatise of political theory finished in 1324, during the conflict between Pope John XXII and Louis of Bavaria. Marsilius, a physician and former rector of the University of Paris, says his aim is to expose the cause of the strife tearing Italy apart. Discourse I argues from reason, largely from Aristotle's Politics. The city exists so that people can live well and sufficiently. Laws are coercive commands, and the legislator is the whole body of citizens or its weightier part (valentior pars). The ruling part, best chosen by election, carries out the law and answers to it. Discourse II argues from scripture and history that Christ and the apostles claimed no coercive power, so priests and bishops have no jurisdiction over anyone in this world. The papal claim to a fullness of power is the hidden cause of discord, and disputes over doctrine belong to a general council. Discourse III lists forty-two conclusions. The book was condemned as heretical in 1327.

It is one of the boldest medieval arguments for popular sovereignty and for confining the Church to the spiritual sphere, and it anticipates later debates about secular government.