In the arsenal of eternal skeptics there are few tools more dramatically and more commonly used than Ockham's razor. It is triumphantly applied to resolve arguments about ghosts (more parsimoniously seen as misperceptions by distraught family members or the suggestible), UFOs (evidently hoaxes and mistaken observations of natural phenomena) and telepathy (a "delusion" of wishful thinking and poorly-constructed tests).
Born in England, Franciscan monk William of Ockham (c. 1287–1347) is among the most prominent figures in the history of philosophy during the High Middle Ages. The Skeptics Dictionary quotes the Razor as Pluralitas non est ponenda sine necessitate, or "plurality should not be posited without necessity," while Wikipedia defines Ockham's razor as follows:
"Among competing hypotheses, the one that makes the fewest assumptions should be selected."
And it gives the following example of its application:
"It is possible to describe the other planets in the Solar System as revolving around the Earth, but that explanation is unnecessarily complex compared to the contemporary consensus that all planets in the Solar System revolve around the Sun."
Another often-quoted formulation of the principle is that "one should not multiply entities beyond necessity."
Brother Ockham, however, said nothing of the kind. Later philosophers have put these words into his mouth for their own convenience.