Abstract
In Bermúdez 2013 I argued against David Lewis’s well-known and widely accepted claim that Newcomb’s problem and the prisoner’s dilemma are really notational variants of a single problem. Mark Walker’s paper in this journal (Walker, Philosophia, 42, 841–859, 2014) takes issue with my argument. In this note I show how Walker’s criticisms are misplaced. The problems with Walker’s argument point to more general and independently interesting conclusions about, first, the relation between deliberation and decision and, second, the differences between the prisoner’s dilemma, which is a strategic choice problem, and Newcomb’s problem, which is a parametric choice problem.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
Notes
In the following I adopt the convention by which player A is female and player B is male.
Admittedly, there is a potential difficulty here. In what sense is a non-admissible option feasible? If I am rational and know myself to be rational, and the principles of rationality rule out the non-admissible options, then how can the set of feasible options be a proper subset of the admissible options? For discussion see Levi 1986, Jeffrey 1977, and Schick 1979. Levi’s solution is that feasibility is an epistemic state. An option is feasible if choosing it is not ruled out by what the agent knows. As long as we do not require that the agent knows that she will only choose an admissible action, non-admissible feasible options remain open. This seems reasonable. The agent may believe, for example, that the process of deliberation will change what is in the set of admissible options – or she may entertain the possibility of some sort of psychological trembling hand or other exogenous factor.
This is an important point, because it blocks off responses to my argument that, in effect, weaken the notion of replica in play to open up the possibility of me and my replica behaving differently. As an anonymous referee suggested, for example, the replica might be a perfect copy of me up to the moment of replication, but then might diverge through some random process. It is true that such a replica would cease to be a mimic, thus opening up the possibility that all four outcomes are really feasible. But the price is significantly weakening the key premise in Lewis’s argument assimilating PD and NP – viz. the extent to which the replica’s choice predicts my choice, which is what allows him to argue for the equivalence of (3) and (3*).
I am grateful to an anonymous referee for encouraging me to address this issue.
As is familiar from discussions of the (so-called) paradox of backward induction, if we do not allow the possibility of non-equilibrium behavior, then it will be very difficult to establish that a particular outcome is the equilibrium outcome. In order to establish that (Defect, Defect) is the Nash equilibrium in PD we need to establish counterfactuals of the type: “If player A were to Cooperate, then the best response for player B would be to Defect”. If the (out-of-equilibrium) antecedent were truly impossible, then all such counterfactuals would come out as trivially true, on standard accounts of counterfactuals.
References
Aumann, R. (1987). Correlated equilibrium as an expression of Bayesian rationality. Econometrica, 55, 1–18.
Bermúdez, J. L. (2013). Prisoner’s dilemma and Newcomb’s problem: why Lewis’s argument fails. Analysis, 73, 423–429.
Bermúdez, J. L. (2015). Prisoner’s dilemma cannot be a Newcomb problem. In M. B. Peterson (Ed.), The Prisoner’s Dilemma (pp. 115–132). Cambridge: Cambridge University Press.
Elster, J. (1979). Ulysses and the sirens: Studies in rationality and irrationality. Cambridge: Cambridge University Press.
Jeffrey, R. (1977). A note on the kinematics of preference. Erkenntnis, 11, 135–141.
Levi, I. (1986). Hard choices. Cambridge: Cambridge University Press.
Lewis, D. (1979). Prisoners’ dilemma is a Newcomb problem. Philosophy and Public Affairs, 8(3), 235–240.
Luce, R. D., & Raiffa H. (1957). Games and decisions: Introduction and critical survey. New York: John Wiley.
Schick, F. (1979). Self-knowledge, uncertainty, and choice. British Journal for the Philosophy of Science, 30, 235–252.
Walker, M. T. (2014). The real reason why the prisoner’s dilemma is not a Newcomb problem. Philosophia, 42, 841–859.
Author information
Authors and Affiliations
Corresponding author
Additional information
I am grateful to an anonymous referee for insightful and helpful comments.
Rights and permissions
About this article
Cite this article
Bermúdez, J.L. Strategic vs. Parametric choice in Newcomb’s Problem and the Prisoner’s Dilemma: Reply to Walker. Philosophia 43, 787–794 (2015). https://doi.org/10.1007/s11406-015-9606-6
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11406-015-9606-6