Within philosophy, hallucinations have served as a paradigmatic test-case for epistemology in general and for theories of perception in particular. The differentiation of hallucinations from “real-life-perception” poses some interesting problems. Here, I will focus on two opposing views: first the view of hallucination as a failure of a metacognitive ability, and second a phenomenologically based view of hallucinations as a disturbance of experiential world-directedness.

Our theoretical understanding of hallucinations however, should take the highly unsettling existential effects on the patients themselves into account as well. As one admits to have experienced a hallucination, this calls into question one's entire capability of perception in general. For how can one be sure not to be hallucinating again? The loss of a basic trust in one's own senses can be so stressful as to aggravate the existing symptoms. These existential effects show that perception cannot be taken as a singular faculty and strengthen the phenomenological approach to hallucinations.