The concept of "everyday cognition" is one of those indeterminate concepts that one must try to define before one can say very much about it. Part of the problem is that the concept is implicitly defined by contrast with "formal" or "academic" cognition. Everyday cognition refers to forms of thinking that are not included within the boundaries of formal or academic cognition. The problem is to say something affirmative about a concept that, in the first instance, is negatively defined. The problem of definition leads to a dilemma involving representativeness and rationality. On the one hand, everyday cognition is believed to be worth studying because it is more representative of human thought in general than formal cognition. On the other hand, formal thought and formal logic in particular have been considered for centuries as prototypical for human rationality. The dilemma consists in the necessity of choosing between the propositions (a) that much of everyday cognition is irrational to the extent that it deviates from formal thinking, or (b) that formal thought and formal logic are not the best or only standards of human rationality.