# Occam's Razor

> When explanations fit equally well, prefer the one with fewer assumptions.

Chapter III, Problem solving · 3.15 · Origin: William of Ockham (14th century) · Time: 15 to 30 min · Solo or group

**Use it when** several explanations fit and you need one to act on.

Interactive workspace: https://kogu.tools/tools/occams-razor

## Abstract

When something needs explaining, the most interesting story is tempting. Occam's razor, named after the fourteenth century logician William of Ockham, says you shouldn't add assumptions you don't need.

It only breaks ties. If a more complicated explanation fits the evidence better, it still wins. This tool has you count the assumptions behind each explanation and rate how well it fits, then ranks them and suggests a test that would tell the top two apart.

## Method

1. **Describe what happened.** Write down the facts that need explaining, as plainly as you can.
2. **List the explanations.** Write down every reasonable explanation, including the boring ones.
3. **Count the assumptions.** For each one, list what else would have to be true for it to hold.
4. **Rate the fit.** Judge how well each explanation covers all the facts, including the dull ones.
5. **Rank and test.** Prefer the best fit and use the assumption count to break ties. Then look for evidence that would separate the top two.

## When to use it

- Several stories could explain a problem and the team keeps drifting to the dramatic one.
- You're working out why a bug happened or why a number dropped.
- Someone makes a claim that needs a lot of things to line up at once.

## Common pitfalls

- Using simplicity to overrule evidence. The razor only chooses between explanations that fit equally well.
- Counting words instead of assumptions. A short explanation can hide a lot of them.
- Settling on the simplest story without testing it.
- Forgetting that the world is sometimes complicated. The razor gives you a first guess to test.

## References

- Spade, P. V. (Ed.) (1999). The Cambridge Companion to Ockham. Cambridge University Press.
- Sober, E. (2015). Ockham's Razors: A User's Manual. Cambridge University Press.
- Baker, A. (2022). Simplicity. In E. N. Zalta (Ed.), The Stanford Encyclopedia of Philosophy.