We explain what people think and do by citing their reasons, but how do such explanations work, and what do they tell us about the nature of reality? Contemporary efforts to address these questions are often motivated by the worry that our ordinary conception of rationality contains a kernel of supernaturalism--a ghostly presence that meditates on sensory messages and orchestrates behavior on the basis of its ethereal calculations. In shunning this otherworldly conception, contemporary philosophers have focused on the project of "naturalizing" the mind, viewing it as a kind of machine that...