Proposed that such assessments occur because the meaning of most characteristics is ambiguous, which allows people to use self-serving trait definitions when providing self-evaluations. Studies 1 and 2 revealed that people provide self-serving assessments to the extent that the trait is ambiguous, that is, to the extent that it can describe a wide variety of behaviors. Study 3 more directly implicated ambiguity in these appraisals. As the number of criteria that Ss could use in their evaluations increased, Ss endorsed both positive and negative characteristics as self-descriptive to a greater degree. Study 4 demonstrated that the evidence and criteria that people use in self-evaluations is idiosyncratic. Asking Ss explicitly to list the evidence and criteria they considered before providing self-evaluations did not influence their self-appraisals. However, requiring Ss to evaluate themselves using a list generated by another individual caused them to lower their self-appraisals. Discussion centers on the normative status of these self-serving appraisals, and on potential consequences for social judgment in general.