How to Use Occam's Razor Without Getting Cut
Farnam Street (Shane Parrish), after William of Ockham · 2019
"Among competing explanations that fit the evidence equally well, the one that requires the fewest assumptions should be preferred — but Occam's Razor is a tool for narrowing initial hypotheses, not a substitute for evidence, and misapplying it (assuming 'simple' always beats 'accurate') can mislead badly."
Occam's Razor states that among hypotheses making equally accurate predictions, the one requiring the fewest assumptions should be preferred, because it's easier to verify, falsify, and act on — the classic medical version is 'when you hear hoofbeats, think horses, not zebras,' meaning doctors should favor the most common explanation for a set of symptoms over a rare, exotic one, all else being equal.
The mechanism is practical, not metaphysical: a simpler hypothesis is easier to test and falsify (fewer moving parts that could be wrong in undetectable ways), and simpler solutions are cheaper to fund and execute — but the razor only applies when the competing explanations genuinely make the same predictions; it does not mean 'the simplest-sounding story is always true' regardless of the actual evidence, a common misreading the piece explicitly warns against.
What is the classic medical-training version of Occam's Razor mentioned in this piece?
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The explanation above is written with AI assistance. These are the originals — go to them to check it.
- Hanlon's Razor (the complementary mental model)Farnam Street
- The Illusion of TransparencyFarnam Street
Second-Order Thinking
"First-level thinking says 'and then what?' once. Second-level thinking keeps asking."