Occam's Razor

TL;DR

• Prefer explanations that make the fewest assumptions when multiple hypotheses exist.
• Use the simplest plausible explanation first to guide investigation and troubleshooting.
• It is a heuristic, not an infallible rule; further testing may be required.

Definition

Occam’s Razor is a principle that suggests that when faced with multiple explanations for a phenomenon, the simplest explanation is most likely the correct one. This principle is named after the 14th-century English logician and Franciscan friar William of Ockham, who is credited with being its originator.

Explanation

Occam’s Razor advises selecting the explanation that introduces the fewest additional assumptions or steps among competing hypotheses. It serves as a heuristic to narrow potential explanations and guide where to begin investigation, without asserting that the simplest option is always correct.

Examples

Light bulb example

Imagine trying to explain why a light bulb in a living room is not turning on. Potential explanations include:

• The light bulb is burnt out and needs to be replaced.
• The light switch is faulty and needs to be replaced.
• There is a problem with the electrical outlet and it needs to be repaired.
• There is an issue with the wiring in the wall and it needs to be fixed.

Occam’s Razor would suggest the simplest explanation—the light bulb is burnt out and needs to be replaced—because it requires only one step and no further repairs.

Medical example

Imagine a patient experiencing fever, cough, and difficulty breathing. Potential explanations include:

• The patient has the flu.
• The patient has pneumonia.
• The patient has lung cancer.

Occam’s Razor would suggest the simplest explanation—the patient has the flu—because it requires only one step (treating the flu) and does not require further investigation or treatments.

Notes or pitfalls

• Occam’s Razor is a useful heuristic but not a strict rule; the simplest explanation is not always correct.
• It is intended to help narrow possibilities and guide further investigation rather than to provide definitive proof.

Related terms

• William of Ockham — the 14th-century English logician and Franciscan friar credited with originating the principle.