Diagnose before elaborating
Check the common, simple explanation first before searching for rare or complex ones.
Why it works
Cognitive availability bias makes vivid, unusual explanations feel probable because they are memorable. But base rates favor common explanations: the classic medical aphorism 'when you hear hoofbeats, think horses not zebras' encodes the same logic. Occam’s Razor applied to diagnosis means starting with the most prevalent cause that fits the evidence, not the most interesting one.
How to do it
- List the top two or three most common explanations for the symptoms or situation you observe.
- Check whether the common explanation is definitively ruled out by evidence before escalating.
- Add complexity only in proportion to the evidence that demands it.
- Document what finding would make you upgrade to a more elaborate explanation.
Evidence
The heuristic 'common things are common' is taught explicitly in clinical medicine and is grounded in base-rate reasoning. Anchoring on rare diagnoses before excluding common ones is a recognized source of clinical error. Croskerry documents this as a cognitive error pattern, and Tversky and Kahneman's work on the availability heuristic explains why vivid rare explanations feel more probable than the base rates warrant. (clinical)
In medicine, zebras do exist; the razor is a triage tool, not a reason to stop investigating when common explanations are genuinely ruled out.
Sources
- Croskerry, Pat (2003). "The Importance of Cognitive Errors in Diagnosis and Strategies to Minimize Them." Academic Medicine, 78(8), 775–780.
- Tversky, Amos & Kahneman, Daniel (1973). "Availability: A Heuristic for Judging Frequency and Probability." Cognitive Psychology, 5(2), 207–232.
- Tversky, Amos & Kahneman, Daniel (1974). "Judgment under Uncertainty: Heuristics and Biases." Science, 185(4157), 1124–1131.
Common mistake
Jumping to elaborate explanations because the problem feels important or complex — importance does not raise the probability of a rare cause.
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More practices for Occam’s Razor: Prefer the Simpler Explanation
- Count the assumptions each explanation requires
When two explanations fit the facts, count how many unverified assumptions each one rests on.
- Resist conspiracy escalation
When your explanation requires others to have coordinated secretly, apply the razor hard.
- Trim model complexity
Prefer the simplest model of a situation that still fits all the evidence.
- Know when not to apply the razor
Occam’s Razor is a tiebreaker, not a rule: when evidence clearly supports complexity, go there.
- Resist the single-cause trap
Simple doesn’t always mean one cause — sometimes the simplest honest answer is 'multiple contributing factors.'
- Apply parsimony to your own communication
Use the fewest words and concepts that carry the full meaning — not as brevity, but as clarity.
Related concepts
- Hanlon's Razor: Never Attribute to Malice What Stupidity Can Explain
The charitable-attribution heuristic and why it usually serves you better
- Thinking, Fast and Slow, Made Usable
Two systems, the biases they create, and when to slow down
- First-Principles Thinking, Made Usable
Reasoning up from fundamentals, with the mechanism behind why it beats analogy
- Anchoring Bias in Negotiation and Judgment
Why the first number wins — the mechanism, and how to set and resist anchors