What is Occam’s razor?

The principle that the explanation with the fewest assumptions is usually the best starting point — simpler theories are more probable and easier to test.

Does Occam’s razor mean the simplest answer is always right?

No. It says simpler explanations are the best default to test first, not that they’re guaranteed true. Reality is sometimes genuinely complex.

What’s an everyday example of Occam’s razor?

If your car won’t start, check the simple cause (empty tank, dead battery) before assuming a rare electronic fault — “think horses, not zebras.”

Occam’s razor

Also called law of parsimony · Logic & science

Occam’s razor is the principle that, among competing explanations, the one requiring the fewest assumptions is usually the best place to start. Simpler explanations are more likely and easier to test — not always right, but the right default.

How it works

Each extra assumption is another thing that can be wrong, so simpler hypotheses have fewer ways to fail and are easier to disprove. It’s a heuristic for prioritising what to test first, not a law of truth.

How to use it

Facing a puzzle, test the simplest plausible explanation first.
Be suspicious of theories that need many special conditions to hold together.
When debugging or diagnosing, check the common, simple cause before the exotic one.

Worked example

Your website is down. Occam’s razor says check the simple causes first — expired domain, a typo in the config, the server switched off — before theorising about a coordinated attack. “When you hear hoofbeats, think horses, not zebras.”

Where it fails

Reality is sometimes genuinely complex, and the simplest explanation can be wrong. It’s a starting heuristic, not a guarantee — don’t amputate necessary complexity.

The deeper point

Occam’s razor isn’t about truth — it’s about test order. The simplest explanation isn’t the most likely to be right; it’s the cheapest to check and easiest to rule out, which is why you start there, not why you stop there.

Frequently asked

What is Occam’s razor?: The principle that the explanation with the fewest assumptions is usually the best starting point — simpler theories are more probable and easier to test.
Does Occam’s razor mean the simplest answer is always right?: No. It says simpler explanations are the best default to test first, not that they’re guaranteed true. Reality is sometimes genuinely complex.
What’s an everyday example of Occam’s razor?: If your car won’t start, check the simple cause (empty tank, dead battery) before assuming a rare electronic fault — “think horses, not zebras.”

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Editorial synthesis © ReadGlobe 2026, drawing on the mental-models tradition (Charlie Munger, Farnam Street) and the primary sources for each model. · Last reviewed 2026-05-29.