Occam’s and Other Razors

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William of Ockham CC BY-SA 3.0, Link

I was explaining recently to someone a reference in the program The Undoing to Occam’s razor. It’s a pretty well-known problem-solving principle, sometimes called the principle or law of parsimony. It states that simpler explanations are more likely to be correct and that you should avoid unnecessary or improbable assumptions.

But why a “razor”?  The principle is attributed to William of Ockham (or Occam), an English Franciscan friar, scholastic philosopher, and theologian, who is believed to have been born in Ockham. But the principle had nothing to do with his shaving habits.

In philosophy, a razor is a principle or rule of thumb that allows one to eliminate (“shave off”) unlikely explanations for a phenomenon, or avoid unnecessary actions.

There are several other razors or razor-like principles that you hear referenced or applied less often.

Paul Grice, a philosopher of language, also has a razor principle of parsimony. Parsimony refers to the quality of economy or frugality in the use of resources. For linguistic explanations, conversational implications are to be preferred over semantic context. This gets more complicated than Occam’s Razor. Grice worked in pragmatics, a subfield of linguistics and semiotics that studies how context contributes to meaning.

I am a fan of the simpler Hanlon’s razor: Never attribute to malice that which can be adequately explained by stupidity.

Hitchens’s razor seems appropriate to much in the news the past decade: What can be asserted without evidence can be dismissed without evidence.

Hume’s Guillotine is a larger and more complex razor: What ought to be cannot be deduced from what is. “If the cause, assigned for any effect, be not sufficient to produce it, we must either reject that cause or add to it such qualities as will give it a just proportion to the effect.” Hume’s law or Hume’s guillotine is the thesis that, if a reasoner only has access to non-moral and non-evaluative factual premises, the reasoner cannot logically infer the truth of moral statements.  This is also less-interestingly called the is-ought problem.

The Sagan Standard is a neologism abbreviating the aphorism that “extraordinary claims require extraordinary evidence.” It is named after Carl Sagan who used that exact phrase on his television program Cosmos, though he was not the first to state it. It illustrates a core principle of the scientific method and of skepticism.

Karl Popper’s falsifiability principle: comes from the philosophy of science. For a theory to be considered scientific, it must be falsifiable. For example, the statement “All swans are white” is falsifiable because “Here is a black swan” contradicts it. That seems clear. But what about “All men are mortal”? It is not falsifiable because, unlike a swan being black, a man being immortal is not an inter-subjective property—there is no shared procedure to systematically conclude to immortality. You can think about that one for a bit.

The exciting Newton’s Flaming Laser Sword (I’m not making up these names.), states that “If something cannot be settled by experiment or observation, then it is not worthy of debate.” It is also known by the less exciting name of Alder’s Razor.


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A lifelong educator on and off the Internet. Random by design and predictably irrational. It's turtles all the way down. Dolce far niente.

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