This dissertation explores issues in the philosophy of psychology and metaphysics through the lens of the emotion of disgust, and its corresponding property, disgustingness. The first chapter organizes an extremely large body of data about disgust, imposes two constraints any theory must meet, and offers a cognitive model of the mechanisms underlying the emotion. The second chapter explores the evolution of disgust, and argues for the Entanglement thesis: this uniquely human emotion was formed when two formerly distinct mechanisms, one dedicated (...) to monitoring food intake and protecting against poisons, the other dedicated to protecting against parasitic infection, where driven together until they became functionally integrated. The third chapter explores the sorts of acquisition mechanisms that could give rise to the patterns of individual and cultural level variation we find with disgust elicitors. It argues for the Empathic Acquisition thesis, which holds that one important route for the social acquisition and transmission of disgust elicitors is linked to empathic recognition of facial expressions of the emotion. The fourth chapter builds on the Entanglement thesis, and embeds the emotion of disgust in gene-culture coevolutionary theory and the tribal instincts hypothesis. The Co-opt thesis is defended, which maintains that disgust was co-opted to play an important role in our moral psychology, particularly in our cognition of social norms and ethnic boundary markers. In doing so, however, it brings to bear many features initially linked to poisons and parasites. This explains the puzzling and troublesome character of moral judgments linked to disgust. After shifting gears from psychology to metaphysics, the fifth chapter recasts the Humean tradition of projectivism in the terminology of cognitive science. Using examples such as disgust, I argue that a psychologized projectivism is able to make sense of the idea that some properties are projected onto the world, rather than found there to begin with. The final chapter criticizes three other accounts of the property of disgustingness, two inspired by functionalism in the philosophy of color, one inspired by fittingness accounts in metaethics. I argue that none provide nearly as satisfactory account of the property as the psychologized projectivism articulated previously. (shrink)