In the academy, the study of morality has historically been a special province of philosophy, while the study of mental processes has, for the past century or so, largely been the province of psychology and allied sciences. At the same time, recent philosophy has been largely speculative or theoretical (despite the robust empirical interests of many canonical philosophers), while the methods of contemporary psychology have characteristically been empirical or experimental (despite the robust theoretical interests of many canonical psychologists). The results have been uneven: philosophy has often been light on fact, and psychology has often been light on theory.

Yet the discipline of moral psychology is, as the name intimates, a hybrid inquiry, informed by both ethical theory and psychological fact. Different practitioners will, quite reasonably, favor different admixtures of fact and theory, but central questions in the field—What is the nature of moral judgment? Why do people behave well or badly?—want empirically informed answers, while developing these answers in theoretically sophisticated ways requires delicate inquiry in philosophical ethics.

Starting in the late 1960s, the increasing influence of philosophical naturalism and cognitive science, particularly in epistemology and philosophy of mind, set the stage for an interdisciplinary study of morality in philosophy, while in psychology, the demise of behaviorism enabled empirical investigation of an

increasing variety of topics, including those that had previously been under the ambit of philosophical ethics. Since the early 1990s, such inquiry has increased exponentially, and by the twenty-first century’s inception, not only were philosophers and psychologists liberally sampling the empirical and theoretical

riches available in their sister disciplines, they had begun to collaboratively produce research aimed at illuminating problems that had previously been treated within the borders of individual fields. The result is not a new discipline, since research appropriately termed moral psychology has long been produced in a variety of subfields, but a resituated discipline, one straddling disciplinary boundaries or—better yet—regarding such demarcations as of little more than administrative interest. (Quoted from the textbook’s introduction; see below)