Occam's Razor

Occam's Razor

by Richard Rockley

Skeptics frequently talk about Occam’s Razor. They use it to choose between alternative explanations for something, especially where no one alternative has been either proven or disproven. But what is it?

Many people will tell you it says, “Choose the simplest solution”. But it doesn’t say choose the simplest solution. Opponents of Occam complain that it will not necessarily help you choose the correct solution. But Occam’s Razor does not pretend to choose the correct solution. So what is it and what is its point?

Occam’s Razor actually says:

“Pluralitas non est ponenda sine neccesitate”,

which is translated as

“plurality should not be posited without necessity.”

The words are those of the medieval English philosopher and Franciscan monk William of Ockham (ca. 1285-1349).

The archaic English needs to be interpreted for modern times. What it means is this:

Do not invent unnecessary entities to explain something.

An example

Suppose I have a cat. One night, I leave out a saucer of milk, and in the morning the milk has gone. No one saw who or what drank the milk. Lets say there are two possibilities:

  1. The cat drank it
    or
  2. The milk fairy drank it

Occam tells us to reject option 2. This is because option 2 requires us to invent an unnecessary entity – the milk fairy. It is an invention because we have no proof that the milk fairy exists. And it is unnecessary because there is a plausible explanation that does not require the milk fairy – the cat. (We know he exists.)

Note: we haven’t proven that the cat drank the milk. Or disproven the milk fairy option. Strictly speaking, we keep an open mind about both options. But Occam says that if you insist it could be the milk fairy, you have invented an unnecessary entity. And why would you do that?

Note also that strictly speaking, both solutions are equally simple. The cat hypothesis is only simpler in that you haven’t had to invent a new, unproven entity. Also note that there are additional options that we could choose if we abandon Occam. For example, it could have been ghosts, or aliens, or the boogieman or Santa Claus. Why choose one of these over the others when there is an equal lack of proof for any of them?

Occam Applied

Occam can be applied to a myriad of supposed paranormal events, including ghosts, psychics, UFOs, people who talk with the dead, reincarnation, the soul, spoon benders, near death and out of body experiences. Usually, the paranormal explanation for these phenomena cannot be disproven, and this is often given as the reason we should consider the paranormal explanation. But Occam says go with the natural explanation for now, until any new evidence challenges it. But if there is a natural explanation and you believe, without proof, that the paranormal one is possible, you are inventing the milk fairy.

Richard Rockley runs Skeptico.