According to David Lewis, the prisoner's dilemma (PD) and Newcomb's problem (NP) are really just one dilemma in two different forms (Lewis 1979). Lewis's argument for this conclusion is ingenious and has been widely accepted. However, it is flawed. As this paper shows, the considerations that Lewis brings to bear to show that the game he starts with is an NP equally show that the game is not a PD.

This book was first published in 1984, as the revised edition of a 1979 original. The text is composed of studies in a descending sequence from perfect rationality, through imperfect and problematical rationality, to irrationality. Specifically human rationality is characterized by its capacity to relate strategically to the future, in contrast to the myopic 'gradient climbing' of natural selection. There is trenchant analysis of some of the parallels proposed in this connection between the biological and the social sciences. In the (...) chapter on imperfect rationality the crucial notion is that of 'binding oneself', as Ulysses did before setting out to the Sirens, when weakness of will may prevent us from using our capacity for perfect rationality. The second half of the book deals with rational-actor theory, comparing its logical power and success to rival approaches, and with the varieties of irrationality expressed in contradictory beliefs and desires. (shrink)

It is commonly thought, in line with the position defended in an influential paper by David Lewis, that the decision problems faced in the prisoner’s dilemma and the Newcomb situation are essentially the same problem. José Luis Bermúdez has recently attacked the case Lewis makes for this claim. While I think the claim is false, I contend that Bermúdez’s reason for rejecting Lewis’s argument is inadequate, and then outline what I take to be a better reason for doing so.