Review of Evidence, Decision and Causality

Abstract

Arif Ahmed, Evidence, Decision and Causality. Cambridge: Cambridge University Press ð2014Þ ,i x1250 pp., $95.00 ðclothÞ. 1. Introduction. Causal and evidential decision theorists disagree on what beliefs one should consult when making a choice. The former hold that a person should consult her beliefs about the causal relationship between her options and the outcomes that might result from them, but the latter think that a person should base her choice on her beliefs about the evidential relationship between her options and their possible outcomes. The difference between causal and evidential decision theory is irrelevant for most practical purposes. However, the two theories give conflicting advice in those ðrare but often realisticÞ choice situations in which good or bad outcomes are evidentially but not causally related to the options an agent is faced with. The so-called Newcomb problem ðNozick 1969Þ is a particularly vivid ðalbeit unrealisticÞ example of where causal and evidential decision theory disagree. Suppose you are faced with two boxes, one of which ðthe ‘transparent’ boxÞ you know contains $1,000, and the other ðthe ‘opaque’ boxÞ might ðbut is not certain toÞ contain $1,000,000. You are given the choice between taking both boxes and just the opaque one. But before you make the choice, you learn that a predictor, who has been incredibly accurate in his past predictions of choices in this type of situation, has put the million in the opaque box just in case he predicted that you will take that box only. What should you choose? Causal decision theory recommends taking both boxes, since nothing you do now will causally affect whether the million is in the opaque box. But evidential decision theory recommends taking only the opaque box, since everyone