Occam’s Razor

Details
Full Name

Occam’s Razor (also spelled Ockham’s Razor)

Also known as

Law of Parsimony, Principle of Parsimony, Lex Parsimoniae, "Entities should not be multiplied beyond necessity"

Core Concepts:

Core rule

Among competing hypotheses that explain the same observations equally well, prefer the one that requires the fewest assumptions. The razor shaves off unnecessary entities, causes, or mechanisms.

What it is not

  • Not a rule to be brief or terse — that is a stylistic choice, not an epistemic one.

  • Not a proof that the simpler answer is true — only a guide to which hypothesis to prefer, investigate first, or commit to under uncertainty.

  • Not a licence for KISS-style solution simplification — Occam operates at the level of explanations, KISS at the level of solutions. They overlap but are not the same razor.

How it is used

  • As a selection filter under uncertainty — when two stories fit the data, start with the one that assumes less.

  • As a debugging heuristic — before assuming a bug requires a race condition plus caching layer plus stale DNS, check whether a single off-by-one explains everything.

  • In architecture decisions — a design that needs three new components to justify itself is evidentially weaker than one that reuses existing pieces.

  • In diagnostic reasoning — prefer explanations grounded in the system’s known mechanics over ones that require novel failure modes.

Limits and counters

The razor is a prior, not a verdict. Reality is frequently non-parsimonious, and "simpler" is relative to a chosen ontology. Einstein’s corollary — "as simple as possible, but no simpler" — warns against under-fitting. Pair Occam with evidence, not as a substitute for it.

Key Proponents

William of Ockham (c. 1287–1347, Summa Logicae, Quodlibetal Questions); the principle predates Ockham in Aristotle and Scotus but carries his name due to his repeated methodological use of it. Modernised by Bertrand Russell and formalised as minimum-description-length / Bayesian simplicity priors in 20th-century philosophy of science.

When to Use:

  • Debugging: triage competing theories of a bug before instrumenting for all of them

  • Architecture review: challenge proposals that introduce new components to explain observed requirements

  • Root-cause analysis: pair with Five Whys to avoid stopping at an elaborate but unjustified explanation

  • Incident response: the outage likely has one cause matching the data, not a conspiracy

  • Requirements clarification: pick the interpretation that requires fewest hidden assumptions about the user

  • LLM prompting: ask the model to prefer the explanation with the fewest moving parts when diagnosing

  • KISS Principle - Sibling razor applied to solutions rather than explanations

  • YAGNI - Applies parsimony to future requirements: don’t build what you can’t justify

  • Five Whys - Occam helps pick which "why" to pursue when the chain forks

  • MECE Principle - Both disciplines of hypothesis hygiene; MECE ensures coverage, Occam ranks by parsimony

  • Devil’s Advocate - Devil’s Advocate stress-tests the hypothesis Occam has selected