ABSTRACT
Two central questions about the nature of reasoning have been addressed since Plato's time: At what level of generality and abstraction do rules for reasoning exist? and Is it possible to improve people's reasoning abilities? These two questions are intimately related. Plato, and most subsequent thinkers up until the late nineteenth century, believed that people possess very abstract rules and that, as a consequence, it is relatively easy to improve reasoning. According to this perspective, known as formal disci pline, rules can be taught in the abstract, in the form of mathematics or logic, and they will then be applied across the concrete domains of everyday life. Psychologists and educators through the nineteenth century explained the process by drawing an analogy between physical and mental training: Just as one could exercise the muscles to obtain stronger muscles, so too could one exercise the reasoning faculties to strengthen them.
