In this chapter we come finally to the performance of those subjects, mentioned in chapter 1, who we classified as experts. Ten of these subjects have expertise in one of the content domains – five are experienced parole officers, presumably knowledgeable about why released prisoners return to crime, and five are experienced school teachers, presumably knowledgeable about why children fail in school. Another five subjects – philosophers – are regarded as having expertise in reasoning itself.

We begin with the domain experts, whose performance bears on the complex and important issue of the relation between the form and content of reasoning. To an extent, this issue has been addressed by the performance of subjects from the main sample across the three topics included in the interview. Generally small but consistent differences have appeared in performance across topics, with subjects showing slightly better argumentive reasoning to the degree that they have personal experience related to the topic. Still, the variation, in both degree of personal experience and resulting performance, is not great. Participants in the study for the most part did not have any concentration of experience in any of the topics. What would the effect be, then, if someone did have a great deal of experience directly related to the topic he or she was asked to reason about? Would this experience enhance the quality of reasoning about this topic, relative to a topic for which the person had no special experience? It is these questions that we address in this chapter.