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11 Logic

occam's razor

by William of Ockham

Core Idea

Among competing hypotheses, prefer the simplest one. Entities should not be multiplied beyond necessity. The explanation requiring fewer assumptions is usually better.

key principles

  • 01

    Simplicity as prior

    All else being equal, simpler explanations are more likely true. Complexity requires justification.

  • 02

    Fewer assumptions, fewer failure points

    Each assumption is a place the theory could be wrong. Fewer assumptions means fewer ways to fail.

  • 03

    Not always correct

    Sometimes reality is complex. The razor is a heuristic, not a law. It guides inquiry, not guarantees truth.

  • 04

    Parsimony in practice

    When debugging, check the simple things first. When explaining, use the fewest concepts necessary.

applications

Science
Theory selection
Given two theories with equal explanatory power, prefer the simpler. Ptolemaic epicycles lost to Copernican simplicity.
Debugging
Check the obvious
Is it plugged in? Is the file saved? Start simple before invoking complex failure modes.
Medicine
Common diagnoses first
When you hear hoofbeats, think horses not zebras. Rare diseases are rare; common ones are common.
Conspiracy
Prefer incompetence
Complex conspiracies require coordination. Incompetence requires nothing special. Hanlon's razor is related.

The Principle of Parsimony

William of Ockham, a 14th-century philosopher, articulated the principle: entities should not be multiplied beyond necessity. In modern terms: don’t make things more complicated than they need to be.

This isn’t about truth—sometimes reality is complex. It’s about methodology. Simple explanations should be tried before complex ones, not because they’re certain, but because they’re more testable and more often correct.

Key Quote

“Plurality must never be posited without necessity.” — William of Ockham