What should one do when one is in doubt about the justice of a war one is called to fight? This chapter charts the itinerary of a controversy about the duty of obedience. Starting with Adrian of Utrecht’s strong view that we have a duty not to fight while in doubt, it moves to tutiorist rationales for obedience by Vitoria and Soto followed by probabilistic defenses obedience by Vázquez, and probabilistic defenses of disobedience by Castro Palao and Juan Sánchez. There is an important difference between the defenses of subject disobedience offered by Adrian and Castro Palao and Juan Sánchez. While for Adrian, obedience is trumped by the duty to adhere by one’s conscience (which in his view requires adhering to one’s opinion), for Castro Palao and Sánchez the probability of the opinion that one may not obey extinguishes any presumptive duties of obedience. It was the development and endorsement of probabilism which caused the transition from one conception of civil disobedience to the other.