 Two broad desiderata have governed the project of defining emotions in both philosophy and affective science: (a) Achieving compatibility with ordinary linguistic usage, and (b) Achieving theoretical fruitfulness. A definition that aims exclusively at (a) is a descriptive definition. A definition that aims at (b) at the cost of possibly violating some ordinary intuitions is prescriptive. To secure ordinary language compatibility, traditional philosophers have relied on introspection, thought experiments, casual observation, gleaning of insights from literary texts and other artistic sources, and more recently, experimental tests of ordinary intuitions and of the psychological processes underlying them performed within “experimental philosophy”.