UC Irvine

Does evidence of peer disagreement defeat a subject’s justification to believe? The literature has pursued this question within an intrapersonal frame: a solitary subject, her evidence, and the coherence of her first-order and higher-order attitudes. Within that frame, the disagreeing peer is a delivery mechanism for higher-order evidence, interchangeable with an altimeter reading or a reason-distorting drug. But disagreement is ordinarily encountered between persons: we learn that another disagrees by comprehending her conflicting assertion, and we respond within a norm-governed practice of asserting, challenging, and objecting. This dissertation investigates the epistemic significance of disagreement within that interpersonal frame. Two questions organize the inquiry, both centered on the hearer’s side of an assertoric exchange. When is comprehending a peer’s conflicting assertion epistemically significant, and why is it significant, when it is? And when does a hearer have warrant to object? The first question belongs to the epistemology of testimony; the second to the normativity of assertion. I argue that answering both requires the same thesis: the epistemic norm of assertion (ENA), on which a speaker has warrant to assert only if she knows or has justification to believe what she asserts. The result is that conciliationism is internally unstable. Chapter 1 uncovers a conflict: since we object by asserting, ENA extends to an epistemic norm of objecting; conciliationism is itself committed to the claim that hearers sometimes have warrant to object to peers; together, these two theses entail that such hearers both have and lack warrant to object. Chapter 2 shows that the conciliationist cannot drop ENA: the view’s defeat verdicts in cases of testimony-based evidence of peer disagreement requires a presumptive testimonial entitlement that only a social norm account, in which ENA is ineliminable, can ground. Chapter 3 takes the result of chapters 1 and 2 to show that what would ground conciliationism cannot be true if the view is true. Unlike the familiar self-defeat charge, the instability charge depends on no second-order dispute about conciliationism. An epilogue argues that conciliationism is, moreover, false.