This article explores the Jacobean oath of allegiance as an act of government. It suggests that historians have misread the intentions of the regime in its formulation and enforcement of the oath. Consequently they have underestimated the capacity of the regime to enforce its will on catholic nonconformists. An analysis of contemporary reaction to the oath demonstrates that early modern government could exert its power in ways which revisionist historians have either missed or denied. The oath should be understood as an exceptionally subtle and well-constructed rhetorical essay in the exercise of state power, and this we see in the devastating effect it had on the structure of Jacobean Romanist dissent. The evidence presented here suggests that this statutory oath was not a simple profession of civil allegiance to which English Romanist dissenters responded with a characteristic mixture of paranoia and politically illiterate confusion. Rather it was an exceedingly complex association of religious and political ideas, a diabolically effective polemical cocktail, which did not have to rely merely on the mechanics of a bureaucracy to work its intended course against the Romanist fraction within the English state.