9 - Puzzles of Self-Locating Belief

Summary

The self-sampling assumption can be seen as an indifference principle of self-locating belief: it instructs us to treat all the possibilities that might be in the reference class of observers as equally likely. Indifference principles of self-locating belief are regarded as suspect by some philosophers because they appear to have paradoxical consequences. Notably, an indifference principle of self-locating belief is usually appealed to in the notorious Doomsday Argument, and it also plays a role in the derivation of apparent “anomalous causal powers” in Nick Bostrom's Adam and Eve thought experiments. The recommendation that we should sometimes act as if there were anomalous causal powers seems very hard to accept. I show that reasoning akin to that used in the Doomsday Argument and in the Adam and Eve thought experiments leads to a similar recommendation in a version of the famous Sleeping Beauty problem. All these unattractive recommendations can be avoided if, as required by the BIC, one pays careful attention to the background evidence based on which one assigns probabilities to competing hypotheses and chooses the observer reference class in accordance with that background evidence.