  An analysis of the path-integral approach to quantum theory motivates the
hypothesis that two experiments with the same classical action should have dual
ontological descriptions. If correct, this hypothesis would not only constrain
realistic interpretations of quantum theory, but would also act as a
constructive principle, allowing any realistic model of one experiment to
generate a corresponding model for its action-dual. Two pairs of action-dual
experiments are presented, including one experiment that violates the Bell
inequality and yet is action-dual to a single particle. The implications
generally support retrodictive and retrocausal interpretations.
