Occam’s razor
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.
✦ Widely referenced — cross-referenced 11× across this reference (6 related ideas · 2 comparisons · 2 hubs) · The State of Thinking 2026 →
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.
The simplest explanation isn't the most likely to be right — it's the cheapest to check.
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.
- Counting 'assumptions' is not objective — rival explanations can each look simpler depending on how you carve them up, so the razor can be bent to fit a preferred answer.
- It selects among explanations that fit the evidence equally well; applied before the evidence is in, it becomes an excuse to stop investigating.
- In adversarial settings, an opponent gains by making the deceptive explanation look like the simple one — simplicity is a heuristic honest nature respects but adversaries exploit.
The counter-model: Systems thinking — Occam's razor pushes toward the fewest moving parts; systems thinking insists some outcomes only make sense through interacting loops — knowing when complexity is essential guards the razor's edge.
How to apply it, step by step
- Write out the observation you need to explain.
- List every candidate explanation that fits the known facts.
- For each, count the independent assumptions it requires you to accept.
- Adopt the fewest-assumption explanation as your working hypothesis, not your conclusion.
- Define what new evidence would force you to move to a more complex explanation.
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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The books behind better thinking
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Prefer to read? The canonical picks:
- Thinking, Fast and Slow — Daniel Kahneman
- The Art of Thinking Clearly — Rolf Dobelli
- The Great Mental Models, Volume 1 — Shane Parrish
- Poor Charlie’s Almanack — Charlie Munger
- Super Thinking — Gabriel Weinberg & Lauren McCann
- Seeking Wisdom — Peter Bevelin
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Cite this page
ReadGlobe. (2026). Occam’s razor. https://readglobe.com/model/occams-razor/
"Occam’s razor." ReadGlobe, 29 May 2026, readglobe.com/model/occams-razor/.
Primary source: Wikipedia
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.