Luke Fenton-Glynn (University College London)
The notion that imprecise *credences* are rationally permissible or even mandatory has gained increasing attention. Less well known is that there are powerful arguments that *chances* are sometimes imprecise. I propose a specific principle for how rational credence would calibrate to imprecise chance. The principle entails that imprecision of (known) chances begets imprecision of rational credence. Read one way, this principle, together with the assumption that there exist imprecise chances, provides a strong additional reason for thinking that rational credence is sometimes imprecise. Read another way, it provides a criterion for evaluating claims that certain sets of probabilities constitute imprecise chances.
