Luck , Rationality , and Explanation : A Reply to Elga ’ s “ Lucky to Be Rational ”

I Introduction What is the epistemic significance of discovering that one of your beliefs depends on an irrelevant causal factor? Suppose that you have a relatively high degree of belief in some proposition. Suppose that you then come to learn that your belief was (in part) caused by an irrelevant factor, a factor that does not bear on the truth of the proposition or on your possession of evidence for it. 1 Should you lower your degree of belief in the proposition? One might think that the answer is clearly yes. If one of your beliefs is based on an irrelevant factor, it does not solely reflect the impact of evidence. And so, the thought goes, you ought not to believe it, or at least, you ought not to believe it as strongly. In " Lucky to be Rational, " Adam Elga defends a very different view. 2 To the question of whether you should lower your degree of belief, Elga's answer is: It depends. Each of us possesses standards of reasoning – beliefs about which forms of reasoning are good or bad. If what you discover is that the irrelevant factor caused you to fail to live up to your standards of reasoning, you should lower your degree of belief. If not, not. 3 So long as you have been living up to your standards, you need not lower your degree of 1 This is a rough characterization of the appropriate notion of relevance. The appropriate notion is difficult to define precisely, though the distinction is clear in practice. 2 Also see White (2010) for a careful and illuminating discussion of this issue. 3 More generally, when you discover the existence of an irrelevant factor of one of your beliefs, how much you should lower your degree of confidence in the belief depends on the degree in which you are justified in believing that you failed to live up to your standards of reasoning. Moreover, if you justifiably but falsely believe that you failed to live up to your standards, you should also presumably lower your degree of belief. I'll leave these modifications implicit in what follows.