Occam's razor, used correctly
The simplest explanation is not always right. Here is what the principle actually says and how to use it.
Occam's razor is one of the most quoted ideas in thinking, and one of the most misused. People often say it means "the simplest answer is usually correct". That is not quite right.
Where it comes from#
The principle is named after William of Ockham, a fourteenth-century English friar and philosopher. In its common form it says that you should not multiply entities beyond necessity. In plainer words: do not assume more than you need to explain the facts.
What it really says#
When two explanations account for the evidence equally well, prefer the one that needs fewer assumptions. It is a guide for choosing between theories, not a law of nature.
Note what it does not say. It does not say the world is simple. It does not say a complicated explanation is wrong if the evidence demands it. Many true things are complicated.
An everyday example#
Your plant is dying. One explanation is that you forgot to water it. Another is that a rare disease and a bad batch of soil combined with a mysterious draught. If both fit the facts, start with the first. It needs fewer assumptions, and it is easy to test.
How to use it well#
- Start with the simple cause. Check the obvious things first, such as whether something is plugged in.
- Test it. A simple explanation is only a starting point. Check whether it holds up.
- Change your mind when facts change. If the simple one fails, move to a more complex one without embarrassment.
A common trap#
People use the razor to dismiss ideas they dislike by calling them complicated. That is an abuse. Complexity is not an argument against something true.
Used honestly, the razor is a habit of mind. It says: do not invent extra causes without a reason. Begin with what you know, and add only what the evidence demands.