Evil demon

The evil demon, also known as evil genius, and occasionally as malicious demon or genius malignus, 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 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 Descartes has no body. Some Cartesian scholars opine that the demon is also omnipotent, and thus capable of altering mathematics and the fundamentals of logic, though omnipotence of the evil demon would be contrary to Descartes' hypothesis, as he rebuked accusations of the evil demon having omnipotence.

It is one of several methods of systematic doubt that Descartes employs in the Meditations.