The generic selection criterion that seems to operate most often in theorizing and that
substitutes for validation is the judgment, "that's plausible." The centrality of plausibility to the theorizing process can be understood in the following way. When theorists apply selection criteria to their conjectures, they ask whether the conjecture is interesting, obvious, connected, believable, beautiful, or real, in the context of the problem they are trying to solve. When they ask these questions of the conjecture, the criterion that lies behind the question incorporates considerable past experience with related problems which the theorist brings to bear on the conjecture.