A Puzzle About Desire

The following four assumptions plausibly describe the ideal rational agent. (1) She knows what her beliefs are. (2) She desires to believe only truths. (3) Whenever she desires that P → Q and knows that P, she desires that Q. (4) She does not both desire that P and desire that ~P, for any P. Although the assumptions are plausible, they have an implausible consequence. They imply that the ideal rational agent does not believe and desire contradictory propositions. She neither desires the world to be any different than she thinks it is, nor thinks it is any different than she desires it to be. The problem of preserving our intuitions about desire, without embracing the implausible conclusion, is what I call “the Wishful Thinking Puzzle.” In this paper, I examine how this puzzle arises, and I argue that it is surprisingly difficult to solve. Even the decision theoretic conception of desire is not immune to the puzzle. One approach, the contrastive conception of desire, does avoid the puzzle without being ad hoc, but it remains too inchoate to win our full confidence.