Hybrid Impermissivism and the Diachronic Coordination Problem

Uniqueness is the view that a body of evidence justifies a unique doxastic attitude toward any given proposition. Contemporary defenses and criticisms of Uniqueness are generally indifferent to whether we formulate the view in terms of the coarse-grained attitude of belief or the fine-grained attitude of credence. This paper articulates and discusses a hybrid view I call Hybrid Impermissivism that endorses Uniqueness about belief but rejects Uniqueness about credence. While Hybrid Impermissivism is an attractive position in several respects, I show that it faces a special problem, the diachronic coordination problem, which has to do with coordinating an agent's beliefs and credences over time. I argue that the problem is fatal for Hybrid Impermissivism. I also formulate a logically weaker version of Hybrid Impermissivism which avoids the diachronic coordination problem, but under substantive assumptions about rational credence.