Is A Little Learning Dangerous?

I argue that a little learning is often dangerous even for ideal reasoners who are operating in extremely simple scenarios and know all the relevant facts about how the evidence is generated. More precisely, I show that, on many plausible ways of assigning value to a credence in a hypothesis H, ideal Bayesians should sometimes expect other ideal Bayesians to end up with a worse credence if they gather additional evidence, even when they agree completely about the likelihoods of the evidence given both H and not‐H. This provides a new reason for pessimism about the prospect of disagreeing individuals resolving their disagreement by consulting additional evidence.