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 all-powerful 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 two-fold: both empirical and rational thinking can be completely compromised. This leads to a worrisome argument:

   1. One knows some fact or other only when one can rule out that there is such a demon.
   2. 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 isn't merely toying with our epistemic situation.
   3. 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...