"Justification and Grounding"
A lot of Bayesians draw connections between probability and justification -- for instance, between evidence E raising the probability of hypothesis H and E giving you justification to believe H. Bayesians have defended various measures of how much justification E provides for H, and various theories of why hypotheses can be justified by old evidence. More recently, Bayesians have proposed formal accounts of when justification for a hypothesis counts as being defeated by further evidence. Unfortunately, many of these theories are false. Bayesians have failed to appreciate that propositional justification involves grounding. As a result, some Bayesians conflate relations of justification with relations of probabilistic dependence.
This talk offers a course correction. After discussing examples that serve to sharply distinguish propositional justification from probabilistic dependence, I argue that a number of significant epistemic relations involve grounding, including relations that hold when evidence supports, gives you justification to believe, or gives you reason to believe a hypothesis. Then I apply my account of justification to some existing debates, developing problems for recent Bayesian accounts of epistemic defeat and for several classic responses to the problem of old evidence. Finally, I develop a novel measure of the justification that evidence provides for a hypothesis, where this measure can help us address counterexamples for existing theories of justification, defeat, and old evidence.