Occam's Razor



""You know, [this] has taught me a valuable lesson; the best solution to a problem is usually the easiest one. And I'll be honest -- killing you is hard.""

- GLaDOS, Portal 2

Also called

 * Law of parsimony
 * Law of economy
 * Law of succinctness
 * The Lex Parsimoniae

Occam's Razor is a logical principle first described in the 14th century by William of Ockham, an English Franciscan friar and philosopher. It is often used to evaluate the usefulness of a theory. Its main tenet is that "Entities must not be multiplied beyond necessity." It can be summed up with the phrase "When you hear hoofbeats, think horses, not zebras."

Most theories have a foundation of underlying premises (the aforementioned "entities"), all of which need to be true for the theory itself to be true. Occam's Razor suggests believing the theory with the fewest underlying premises (the aforementioned "not multiplied beyond necessity").

Example: There have been theories that Ancient Astronauts built the Egyptian Pyramids instead of humans. For this to be true, we'd need the following givens: The more normal theory only requires that You can probably guess which theory Occam would agree with, and why.
 * 1) aliens exist,
 * 2) they have some form of interstellar travel,
 * 3) they know how to find us, and
 * 4) once they got here, they'd waste time building huge stone things in a desert instead of, you know, actually showing themselves.
 * 1) humans exist, and
 * 2) said humans would waste time building huge stone things in a desert.

It's the bane of Conspiracy Theorists everywhere for the same reason: take a look at the Apollo moon landings, which a good percentage, in the single figures, believe was hoaxed. Often people will find "evidence" that the landings could never have taken place, but it rests on the arguments that the US government After that, you'd think that the simplest explanation was to, you know, actually send people there (That Mitchell and Webb Look has a brilliant series of sketches on this idea, including the moon landing).
 * 1) were willing to throw billions away for smoke-and-mirrors attempts,
 * 2) were smart enough to fool 90% of the population (which some would contest),
 * 3) were simultaneously stupid enough not to cover their tracks,
 * 4) were able to pay off and swear to silence thousands of people working at NASA and other companies for forty years when they couldn't even pull off a simple burglary, and
 * 5) were actively collaborating with the Soviets during a period of history where relations were historically edgy and were given consent by Moscow to win this symbolic victory.

The Razor is commonly misinterpreted as saying, "The simplest theory is the best." This is not correct in Real Life unless it is the simpler of two theories which make predictions with identical degrees of accuracy. All other aspects of the theory have to be equal before simplicity is taken into account. It also requires that all the data is accounted for. Newtonian physics are simpler then modern theories and were sufficient to take man to the Moon, but (with all due respect to the man) Sir Isaac simply could not explain all the data eventually collected—especially since a lot of the offending material had not been collected when Principia Mathematica was published. This required some other smart man—fellow named Albert Einstein—to formulate more complex theories, particularly the outrageous stew we call "Relativity" which functions along completely different rules. Now, Occam's Razor would suggest that there must be some Grand Unified Theory that explains why physics work one way on an atomic level and completely differently on a larger-than-atomic level. Much of the last century of scientific research (including Einstein's) has centered around trying to come up with one. They haven't succeeded. So far, Occam's Razor is wrong, and the universe simply functions according to completely different sets of rules depending on an object's physical size, for no good reason whatsoever. Nobody likes this, but in the end, nothing says that an explanation must be simple.

Another very common mistake is to summon up the Razor in a debate over a point that is entirely moot in order to add weight to a particular argument. This usage is entirely fallacious as the Razor does nothing more than recommend the hypothesis that makes the fewest new assumptions. It is not a magical tool that points to the right answer. In a lab it will be used hundreds or thousands of times, with each and every one of the chosen hypothesis being rigorously tested, before a correct answer is found. In a debate the Razor will be used once and will, invariably, choose the user's answer as the 'right' one. Funny, that.

And always remember that Occam's Razor is a guideline, not a rule. Be careful of facts that are subjective in nature or may not be fully established.