Critical thinking has been conceptualized as a two-factor system in which critical thinking ability and critical thinking disposition combine to determine actual thinking performance. The present study used confirmatory factor analysis to investigate such a two-factor model empirically. One hundred ninety-eight Purdue University undergraduates completed the Watson-Glaser Critical Thinking Appraisal, the Ennis-Weir Critical Thinking Essay Test, the Need for Cognition Scale (NCS), the AT-20 ambiguity tolerance scale, and the Checklist of Educational Views (CLEV). The students' grade point averages (GPAs) and Scholastic Aptitude Test (SAT) Verbal and Mathematics scores were also collected. The NCS, AT-20, and CLEV served as measures of disposition; Watson-Glaser, SAT-Verbal, and SAT-Math served as measures of thinking ability; and Ennis-Weir and GPA were assumed to measure both ability and disposition. Confirmatory factor analysis indicated that the postulated two-factor model provided a more accurate fit with the data than did a model including only one latent factor and that Ennis-Weir, but not GPA, loads significantly on both factors. (Contains 6 tables and 80 references.) (Author)