In a time of great social change and breathless scientific advance, professional education must equip students with sufficient certainty for today’s practice but with the capacity to live with uncertainty without losing their sense of direction, and with zest for unlearning as well as for new learning. Failure to grapple with the hard task of defining and constantly evaluating objectives can result in not having yardsticks by which to measure the success of students, other than their ability to absorb and reproduce what they have learned in the course. In any professional education it is not possible to do more than give students enough to be getting on with; to start with sufficient momentum so that they are likely to continue on the right lines. The discipline of priorities, of subordinating one’s absorption in the subject to students’ needs, is hard for those teachers whose interest in their subject exceeds their interest in how students learn and for what purposes.