Occam's Razor
When several explanations fit the evidence, prefer the one that does the job with fewer unsupported assumptions. Simpler is not automatically true. It is a better starting point when it explains the evidence adequately.
Among explanations that adequately fit the evidence, prefer the one requiring fewer unnecessary assumptions.
Which explanation accounts for the evidence with the fewest unsupported assumptions?
Diagnosis, troubleshooting, research, strategy and situations with several plausible explanations.
Fast overview
Occam's Razor is a rule of reasoning, not a law of nature. Its classic idea is associated with William of Ockham. The practical lesson is to avoid adding causes, entities or assumptions unless the evidence requires them.
The razor compares explanations that account for the evidence. It does not favor a simple explanation that leaves important facts unexplained.
Mental Model Compass
Learn it progressively
Define the observation
Separate what happened from your interpretation of it.
Generate alternatives
List realistic competing explanations.
Expose assumptions
Ask what must be true beyond the established evidence.
Remove needless complexity
Prefer an adequate explanation that asks you to assume less.
Test what separates them
Find evidence that would distinguish the leading explanations, then update.
Interactive assumption audit
Compare two explanations. Count meaningful assumptions not already established by the evidence. A lower count is a simplicity advantage, not proof.
Explanation A
Explanation B
See it in practice
Technology
A site fails after a deployment. Check a configuration error before assuming an unrelated simultaneous infrastructure failure, while still testing alternatives.
Management
Sales fall after a price increase. Test whether the price change explains the behavior before adding several new causes.
Everyday reasoning
A colleague misses a meeting. Calendar confusion may initially require fewer assumptions than deliberate avoidance. New evidence can change the judgment.
Worked application
Why did sign-ups drop?
Observation: Registration fell sharply after a form change.
Explanation A: The new form introduced friction. It is directly testable and requires one main new assumption.
Explanation B: The market lost interest, competitors changed behavior and audience preferences shifted simultaneously.
Application: Test the form first. If analytics show it works normally, the simpler explanation loses support. The razor guides inquiry. Evidence decides.
Common mistakes
Choosing the shortest story
Few words do not mean few assumptions.
Treating simplicity as proof
The simpler explanation can be wrong. It earns priority for testing, not automatic acceptance.
Cutting required complexity
If evidence requires several causes, removing them makes the explanation worse.
Ignoring evidence
Simplicity cannot override strong observations or relevant prior knowledge.
When not to use it
Do not use Occam's Razor as the sole rule when explanations fit the evidence differently, when rare but serious possibilities must be ruled out or when domain knowledge changes their plausibility. Establish what the evidence supports first. Use simplicity to prioritize testing among adequate explanations.
Related mental models
Bayesian Updating
Combine prior plausibility with new evidence more formally.
First Principles Thinking
Separate what is known from what is assumed.
Inversion
Ask what evidence would show your leading explanation is wrong.
Try It Yourself prompt builder
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Make Occam's Razor reusable in your AI workflow
Compare explanations, expose assumptions and identify the simplest explanation that adequately fits the evidence.