Alex Worsnip

The independence of irrelevant alternatives is a popular and important axiom of decision theory. It states, roughly, that one’s choice from a set of options should not be influenced by the addition or removal of further, unchosen options. In recent debates, a number of authors have given putative counterexamples to it, involving intuitively rational agents who violate IIA. Generally speaking, however, these counterexamples do not tend to move IIA’s proponents. Their strategy tends to be to individuate the options that the agent faces differently, so that the case no longer counts as a violation of IIA. In this paper, we examine whether this strategy succeeds. We argue that the ways of individuating options required to save IIA from the most problematic counterexamples—in particular, cases where agents violate IIA due to nonconsequentialist moral beliefs—do so only at the expense of severely compromising its central function within decision theory

It is standard, both in the philosophical literature and in ordinary parlance, to assume that one can fall short of responding to all one’s moral reasons without being irrational. Yet when we turn to epistemic reasons, the situation could not be more different. Most epistemologists take it as axiomatic that for a belief to be rational is for it to be well-supported by epistemic reasons. We find ourselves with a striking asymmetry, then, between the moral and epistemic domains concerning what is taken for granted about whether failures to respond to reasons are failures of rationality. My aim in this paper is to interrogate this asymmetry, and ultimately to argue that the asymmetry is groundless. Instead, I will offer an error theory to explain the asymmetry in intuitions. This error theory suggests that we should amend the conventional wisdom about the relationship between epistemic reasons and rationality.