Someone please totally copyedit this   Scientists occasionally invent hypothetical entities with special abilities as part of a thought experiment These demons have abilities that are nearly limitless but they are still subject to the physical laws being theorized about  For example in Descartes Second Meditation it is argued as a thought experiment that it is at least possible that there is an allpowerful evil demon who is deceiving me such that this demon causes me to have false beliefs including the belief that there is an object before me and the belief that two plus three equals five Note that the power of such a demon would be twofold both empirical and rational thinking can be completely compromised This leads to a worrisome argument      One knows some fact or other only when one can rule out that there is such a demon     But one can never be in a position rule out that there is such a being since we can never be sure that the demon isnt merely toying with our epistemic situation     Thus we can never know any facts at all   I hate it when people need to be slammed in the face WIKIPEDIA IS AN ENCYCLOPEDIA NOT A COLUMN I was too lazy to understand what it reads there so please someone if that is a joke or something too lazy to think right now then remove it I guess