Evil Demon

The evil demon, sometimes referred to as the evil genius, is a concept in Cartesian philosophy. In his 1641 Meditations on First Philosophy, René Descartes hypothesized the existence of an evil demon, a personification who is "as clever and deceitful as he is powerful, who has directed his entire effort to misleading me." The evil demon presents a complete illusion of an external world, including other minds, to Descartes' senses, where in fact there is no such external world in existence. The evil genius also presents to Descartes' senses a complete illusion of his own body, including all bodily sensations, when in fact Descartes has no body. Most Cartesian scholars opine that the evil demon is also omnipotent, and thus capable of altering mathematics and the fundamentals of logic.

The evil demon has a parallel with Berkeley's concept of a consensus reality supported by God. It is one of several methods of systematic doubt that Descartes employs in the Meditations.