It is argued that contemporary nursing education's emphasis on the conscious development of nurses' critical reasoning skills fails to take account of the complexity of both human cognition and clinical nursing practice. Human cognition centrally includes unconscious or tacit processes and clinical nursing practice is typified by the simultaneous presentation of clinical and non-clinical cues and competing clinical goals. Contemporary emphases on conscious critical thinking are largely consistent with the differing theoretical frameworks which have informed the study of nurses' clinical reasoning in the last 30 years, most of which permit the use of simulated case study. These frameworks, that is, decision theory, information processing and skills acquisition theory, are described and their limitations highlighted. In addition, an alternative theoretical framework, that of schema or script theory, which does take account of the complexities of cognition and practice, is discussed. Its implications for nursing practice and education are also outlined.