Abstract
This lecture is cpncerned with the expected-utility or Bayesian model of rationality, with particular attention both to the strengths and limitations of the model. The alternative market and legal models of rationality are examined and rejected as less satisfactory than the expected-utility model. The role of intuitive judgement in the context of actual decision making is stressed. The fundamental place of intuitive judgement in science, especially in the performance of experiments and the analysis and presentation of results is analyzed. Errors of measurement naturally arise in application of the expected-utility model, but there is a long history of theory and practice for dealing with such errors. The existence of such errors constitutes a limitation, not a prohibition, on the use of expected-utility theory as a fundamental framework for rational behaviour.