Time-slice rationality and filling in plans

In Reasons Without Persons, Brian Hedden argues that a theory of rationality need not provide diachronic norms for reasoning, since we can explain all we need to explain about rationality using purely synchronic norms. This article argues that a theory of rationality should contain at least one diachronic norm for reasoning, namely a norm to fill in the details of one's coarse-grained or partial plans. It also explores a possible synchronic approach to this aspect of rationality.