Branden Fitelson

David Lewis (and others) have famously argued against Adams’s Thesis (that the probability of a conditional is the conditional probability of its consequent, given it antecedent) by proving various “triviality results.” In this paper, I argue for two theses — one negative and one positive. The negative thesis is that the “triviality results” do not support the rejection of Adams’s Thesis, because Lewisian “triviality based” arguments against Adams’s Thesis rest on an implausibly strong understanding of what it takes for some credal constraint to be a rational requirement (an understanding which Lewis himself later abandoned in other contexts). The positive thesis is that there is a simple (and plausible) way of modeling the probabilities of conditionals, which (a) obeys Adams’s Thesis, and (b) avoids all of the existing triviality results.