Psychedelic Epistemology: William James and the “Noetic Quality” of Mystical Experience

William James proposed in 1902 that states of mystical experience, central to his idea of religious experience, can be identified based on their ineffability and their noetic quality. The epistemological category of the noetic quality, modified by W. T. Stace in 1960, plays a central but somewhat confounding role in today’s biomedical research involving psychedelic drugs such as psilocybin and LSD. Using scales based on James, it can be shown that psychedelics “reliably occasion” intense subjective states of experience or mystical states. It is debated whether these states are necessary for the wide range of possible mental health therapeutic benefits that appear to follow. This paper reviews what James said about the noetic quality and its relationship to religious experience, epistemology, and states of mystical experience. It explores how the noetic quality is measured in today’s research, addressing a growing list of concerns that psychedelic science can be epistemologically biased, that it is hostile to atheistic or physicalist views, that it injects religion unduly into science, or that it needs to find ways to eliminate the mystical element, if not the entire intense subjective experience altogether.