Abstract
The paper examines problems for rationality and morality arising out of prisoners' dilemma. Section I criticizes a k sen's attempt to elimate, By variations of preference patterns, The clash between individual rationality and individual or social optimality. Section ii rejects sen's account of morality as a moral ordering of preferences over outcomes, Because it fails to resolve the conflict raised by prisoners' dilemma between individual and social optimality and creates a new conflict between rationality and individual optimality. Section iii sketches accounts of morality and rationality which can avoid these problems. An appendix further explains the distinctions between four kinds of preferences introduced in the paper itself.