When one reads a book on the current state of any field of psychology, whether reasoning or anything else, there can be a tendency to feel a sense of despair because it is so difficult to distinguish what psychologists know about the phenomena in the field, versus what individual psychologists or groups of psychologists believe about those phenomena. Because all psychologists, and especially experts writing about an area, have an opinion on contentious matters, they themselves may lose sight of the difference between what is known and what they believe. I have myself gotten involved in countless debates where scholars spoke as though what they believe is correct and where they view their job as convincing non experts in the field that they are correct and that their opponents are, at best, misled, and, at worst, foolish or even malevolent.

Such debates have a special significance in the study of reasoning, where one would think that reasoning could be used to resolve at least some of these debates. So far, it has not worked. As readers of these chapters can see, the field of reasoning is just as contentious as any other field in psychology. For example, the debate between theorists who prefer rule-based accounts of reasoning, such as O'Brien, and those who prefer mental-models accounts, such as Johnson-Laird, shows no sign of abating at any time in the near future.

Debates such as these can be frustrating to students and other novices in the field, because it is hard, at times, to figure out what, if anything, we really know.