Commonplace Notes

Occam's Razor: When the Simplest Answer Is (Almost Always) the Right One

occam's razor, principle of parsimony, simplicity, william of ockham, scientific method, critical thinking

philosophybiaseslogic

Between Two Explanations, Which One to Choose?

You get home and the door is open.

Explanation A: You forgot to lock it.
Explanation B: Aliens invaded using teleportation technology but took nothing because they were studying human habits.

Which one makes more sense?

Obvious, right? But why is it obvious?

The answer lies in Occam’s Razor: among multiple adequate explanations for the same set of facts, one should opt for the simplest.

It’s not just “common sense”—it’s a logical principle that has guided science, philosophy, and medical diagnoses for centuries.

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What Is Occam’s Razor?

Also called the principle of parsimony. In Latin: “Entia non sunt multiplicanda praeter necessitatem”—“entities must not be multiplied beyond necessity.”

Translating: don’t complicate things if you don’t have to.

The principle states:

  • If two theories explain a phenomenon equally well
  • Choose the one with fewer assumptions
  • Fewer variables, fewer “what ifs
”

Important: This doesn’t mean the simplest explanation is always the true one. It means that, in the absence of contrary evidence, it is the most probable.

Origin: William of Ockham (1288–1347), an English Franciscan friar. He never explicitly formulated it, but he applied this logic so consistently that he became known for it.

Practical Examples

1. Conspiracy Theories

“Man never went to the Moon—NASA filmed it in a studio.”

Complex Explanation:

  • NASA invented everything
  • They bribed thousands of people
  • The Soviets (enemies!) agreed not to expose them
  • The secret has been kept for 50+ years
  • Every space agency in the world is in on the collusion

Simple Explanation: Man went to the Moon.

Which one requires fewer assumptions?

2. Medical Diagnosis

A patient has a fever, headache, and cough.

Complex: Three different diseases appeared at the same time.
Simple: The flu.

Doctors use this all the time—looking for one explanation that covers all symptoms.

3. Your Car Won’t Start

Complex: Electronic system remotely hacked.
Simple: The battery is dead.

Why Does It Work?

Mathematical Probability
Each added element increases the chance of error.

If a theory has 3 assumptions (90% chance each):

  • 0.9 × 0.9 × 0.9 = 72.9% success rate

With 10 assumptions:

  • 0.9^10 = 34.8% success rate

The more elements, the higher the chance of error.

When Does It NOT Work?

Sometimes reality is complex.

Quantum mechanics is absurdly more complex than classical physics—but it is the right explanation for subatomic phenomena.

If scientists had insisted on Newtonian simplicity, they would never have discovered particles.

The lesson: Occam is a heuristic, not a law. Start simple. If it doesn’t work, then add complexity.

Questions I Had (and the Answers)

“Is the simplest explanation always the right one?”
No. It is the most probable in the absence of evidence. But if there is proof of complexity, accept it.

“Who decides what is ‘simple’?”
One counts the number of undemonstrated assumptions. Fewer assumptions = simpler.

“Does this work in real life?”
Yes. When something goes wrong, my brain wants to create complex narratives. Occam makes me ask: “Or did I just forget to save the file?”

Why I Use This in My Daily Life

Because it saves mental energy.

Every time something goes wrong, my brain creates narratives:

  • “Maybe it’s sabotage”
  • “Maybe it’s an ultra-rare bug”
  • “Maybe it’s a conspiracy”

Then I apply Occam:

  • “Or maybe I just got the syntax wrong”
  • “Or maybe I forgot to save”

It’s almost always the second option.

This saves me from paranoia, far-fetched theories, and wasting time investigating improbable things.

💡 Summary in 3 points:

  1. Between equivalent explanations, choose the one with fewer assumptions (Principle of Parsimony).
  2. Simplicity doesn’t guarantee truth, but it is statistically more probable.
  3. Start simple—if it doesn’t work, then add complexity.

Did you enjoy this principle? I’ve written about other philosophical razors. Check out the post on Hanlon’s Razor—it’s about why you shouldn’t assume malice when incompetence explains it better.

Leia também Occams Razor Principle Parsimony Simplicity

References:

Personal note: I need to study critiques of the Razor—especially Walter Chatton’s “anti-razor.” Are there cases where multiplying entities is necessary? That’s for another post.

by J. Victor Resende