Since Whitehead's metaphysics described a universe in which all entities experience, he needed a new way of describing perception that was not limited to living, self-conscious beings. The term he coined was "prehension", which comes from the Latin prehensio, meaning "to seize." The term is meant to indicate a kind of perception that can be conscious or unconscious, applying to people as well as electrons. It is also intended to make clear Whitehead's rejection of the theory of representative perception, in which the mind only has private ideas about other entities. For Whitehead, the term "prehension" indicates that the perceiver actually incorporates aspects of the perceived thing into itself. In this way, entities are constituted by their perceptions and relations, rather than being independent of them. Further, Whitehead regards perception as occurring in two modes, causal efficacy (or "physical prehension") and presentational immediacy (or "conceptual prehension").