Occam’s razor is bandied about quite a bit on the internet, particularly among skeptical circles. Most of my life, I’d assumed that it was identical to the famous Sherlock Holmes axiom from The Sign of the Four (1890): “How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?” And it turns out that, for most of my life, I’ve been wrong. This quote, although it works along similar lines, is not Occam’s razor.
Occam’s razor is actually based on two “laws,” the lex parsimoniae (or law of parsimony) and the lex pluralitatem (or law of plurality, and I’m trusting Google Translate for the Latin on that one). Both must be applied to fully make use of the razor. Even then, as we’ll soon see, it must also be remembered that the razor does not guarantee accuracy. It is merely a tool that gives you a starting point for reasoning about a problem.
The lex parsimoniae can be stated “frustra fit per plura, quod potest fieri per pauciora,” and usually translated into English as “it is pointless to do with more what can be done with fewer.” The lex pluralitatem on the other hand, can be stated “numquam ponenda est pluralitas sine necessitate,” “plurality is never to be posited without necessity.” Combining the two laws, Occam’s razor is, simply put: “Keep it simple. Because, all else being equal, the simplest answer is most likely to be the correct one.”