How We Know What Not To Think.

Humans often represent and reason about unrealized possible actions - the vast infinity of things that were not (or have not yet been) chosen. This capacity is central to the most impressive of human abilities: causal reasoning, planning, linguistic communication, moral judgment, etc. Nevertheless, how do we select possible actions that are worth considering from the infinity of unrealized actions that are better left ignored? We review research across the cognitive sciences, and find that the possible actions considered by default are those that are both likely to occur and generally valuable. We then offer a unified theory of why. We propose that (i) across diverse cognitive tasks, the possible actions we consider are biased towards those of general practical utility, and (ii) a plausible primary function for this mechanism resides in decision making.