Evidential decision theories


by Eliezer Yudkowsky Aug 1 2016

Theories which hold that the principle of rational choice is "Choose the act that would be the best news, if somebody told you that you'd chosen that act."

An "evidential" decision theory (EDT) is one which [action_conditional conditions on possible choices] using standard conditional probabilities, aka Bayesian updating. The corresponding candidate for a [principle_of_rational_choice principle of rational choice] would be, "Choose that act which would be the best news, if somebody told you that you'd decided that way." Contrast Causal decision theories and Logical decision theories. While relatively few decision theorists advocate for EDT as the principle of rational choice, some do. EDT is historically noteworthy for being the original formulation of the principle of expected utility--the formula was first written down with the most obvious kind of [action_conditional action-conditional], namely a standard conditional probability. However, nobody called this "evidential decision theory" until Causal decision theories existed for contrast. See Guide to Logical Decision Theory for a guide to issues surrounding the choice between evidential and other decision theories (as seen from the stance of LDT).