Abstract

Belief polarization occurs when subjects who disagree about some matter of fact are exposed to a mixed body of evidence that bears on that dispute. While we might expect mutual exposure to common evidence to mitigate disagreement, since the evidence available to subjects comes to consist increasingly of items they have in common, this is not what happens. The subjects’ initial disagreement becomes more pronounced because each person increases confidence in her antecedent belief. Kelly aims to identify the mechanisms that underlie this phenomenon and assess whether these processes undermine the justification of polarized beliefs. He concludes that given evidentialism, justification is not undermined by the polarizing mechanisms. I take on board Kelly’s description of the polarizing mechanisms, but challenge his conclusion. I argue that on plausible versions of evidentialism, the beliefs that result from these routes to polarization are not justified.