Milton's status as a political thinker has endured something of a checkered career. Recent scholarship has attended both to the complexity of Milton's character and the classical ideals permeating his political thought. This essay seeks to clarify further Milton's defence of the commonwealth, by situating his polemical writings of 1649 to 1653 in the context of the Engagement debate about the character and extent of loyalty to the new free state. This sheds an interesting and neglected light both on that debate, the presentation of the case of the commonwealth and Milton's distinctive use of casuistry in that presentation.