This research shows that the motivation to posses a desired characteristic (or to avoid an undesired one) results in self-perceptions that guide people's use of base rate in the Lawyer-Engineer problem (Kahneman & Tversky, 1973). In four studies, participants induced to believe (or recall, Exp. 2) that a rational cognitive style is success-conducive (or an intuitive cognitive style failure-conducive) subsequently viewed themselves as more rational and relied more on base rate in their probability estimates than those induced to believe that a rational cognitive style is failure-conducive (or an intuitive cognitive style success-conducive). These findings show that the desired self had an influence on reasoning in the self-unrelated lawyer-engineer task, since the use of base rates was mediated by changes in participants' perceptions of their own rationality. These findings therefore show that the desired self, through the working self-concept that it entails, constitutes another factor influencing people's use of distinct modes of reasoning. (Contains 4 tables.)