Philosophers who take rationality to consist in the satisfaction of rational requirements typically favour rational requirements that govern mental attitudes at a time rather than across times. One such account has been developed by Broome in Rationality through reasoning. He claims that diachronic functional properties of intentions such as settling on courses of actions and resolving conflicts are emergent properties that can be explained with reference to synchronic rational pressures. This is why he defends only a minimal diachronic requirement which characterises forgetting as irrational. In this paper, I show that Broome’s diachronically minimalist account lacks the resources to explain how a rational agent may resolve incommensurable choices by an act of will. I argue that one can solve this problem by either specifying a mode of diachronic deliberation or by introducing a genuinely diachronic requirement that governs the rational stability of an intention via a diachronic counterfactual condition concerning rational reconsideration. My proposal is similar in spirit to Gauthier’s account in his seminal paper ‘Assure and threaten’. It improves on his work by being both more general and explanatorily richer in its application with regard to diachronic phenomena such as transformative choices and acts of will.