Occam's razor
From RationalWiki
Occam's Razor is what Occam shaved with. No, seriously, it refers to a minimalist principle that originates in the medieval philosophical school Nominalism. The principle states that when answering a problem or searching for a cause for something, one should never make more assumptions or posit more causes than the minimum necessary for solving the problem. It is named after the 14th century English philosopher and theologian William of Occam (or Ockham).
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[edit] History
Although the principle bears his name, it was not invented by William of Occam. It is found in the writings of many other medieval philosophers, including Duns Scotus, Thomas Aquinas, and Durand de Saint-Pourcain, and it has roots as far back as Aristotle. However, since Willliam of Occam was one of its most prolific exponents, and since he became involved in a long theological conflict with Pope John XXII because of it, his name has been associated with the principle.
[edit] Common misuse
It is sometimes used fallaciously as a handwave by woo-meisters and creationists to skirt the fact that the point they are arguing requires a completely unknown mechanism (paranormal powers, "Goddidit" etc.) to work properly. This claim states that Occam's Razor prefers to posit that a God does exist and it's simpler to believe Goddidit rather than natural selection and evolution could create the complexity of life. Alternatively, they worm out of a debate by saying that the non-existence of God is an "assumption" - even though the existence or non-existence of a supreme being is completely irrelevant to the naturalistic forces around the world.
Regardless, Occam's Razor is a guideline and not a hard-and-fast ruling. In practice, the subjectivity of minimalism can relegate it to a rhetorical device, rather than an investigatory tool.
[edit] Expressions of the principle
William of Occam often expressed it as Numquam ponenda est pluralitas sine necessitate (A plurality [of causes] should never be posited unless necessary), but the best known expression is a paraphrase by the 17th century scholar John Ponce: Entia non sunt multiplicanda praeter necessitatem (Entities are not to be multiplied beyond what is necessary). When Occam's Razor can be quickly and easily expressed as "don't over-complicate things", you have to wonder why these people didn't pay attention to their own idea a bit more.
In modern terms, it has been expressed as "when you have two competing theories which make exactly the same predictions, the one that is simpler is the better." "Simpler" in this case can also mean "makes fewer (or less onerous) assumptions" - as assumptions may or may not be true and the fewer, or more believable ones, that you have to make, the more you can be sure that they're right. As Travis Dane said, "assumption is the mother of all fuck ups".
