 One controversial argument that it is rational to cooperate in a PD relies on the observation that my partner in crime is likely to think and act very much like I do. (See, for example, Davis 1977 and 1985 for a sympathetic presentation of one such argument and Binmore 1994, chapters 3.4 and 3.5, for a reformulation and extended rebuttal.) In the extreme case, my accomplice is an exact replica of me who is wired just as I am so that, of necessity, we do the same thing. It would then seem that the only two possible outcomes are where both players cooperate and where both players defect. Since the reward payoff exceeds the punishment payoff, I should cooperate. More generally, even if my accomplice is not a perfect replica, the odds of his cooperating are greater if I cooperate and the odds of his defecting are greater if I defect. When the correlation between our behaviors is sufficiently strong or the differences in payoffs is sufficiently great, my expected payoff (as that term is usually understood) is higher if I cooperate than if I defect. The counter argument, of course, is that my action is causally independent of my replica's. Since I can't affect what my accomplice does and since, whatever he does, my payoff is greater if I defect, I should defect. These arguments closely resemble the arguments for two positions on the Newcomb Problem, a puzzle popularized among philosophers in Nozick. (The extent of the resemblance is made apparent in Lewis.) The Newcomb Problem asks us to consider two boxes, one transparent and one opaque. In the transparent box we can see a thousand dollars. The opaque box may contain either a million dollars or nothing. We have two choices: take the contents of the opaque box or take the contents of both boxes. We know before choosing that a reliable predictor of our behavior has put a million dollars in the opaque box if he predicted we would take the first choice and left it empty if he predicted we would take the second. To see that each player in a PD faces a Newcomb problem, consider the following payoff matrix.