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What Is Ockham's Razor? And Is It Ever Useful?

The simplest explanation is usually best? Well, not necessarily.

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Dr. Katie Spalding

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Dr. Katie Spalding

Freelance Writer

Katie has a PhD in maths, specializing in the intersection of dynamical systems and number theory.

Freelance Writer

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Two arrows, one showing a simple path and the other showing a messy complicated path.
If you look closely, it says "Jeremy Bearimy". Image credit: Marie Maerz/Shutterstock

William of Ockham, the 14th-century Franciscan friar and Catholic theologian, probably never expected his name to become synonymous with a scientific principle lasting 800 years after his death. 

That makes sense, since Ockham’s Razor, as we now know the maxim, was around long before William made it popular – John Duns Scotus got there before him, as did Maimonides, Ptolemy, and even Aristotle. None of those thinkers would likely recognize the principle as many of us know it today: the idea that “the simplest solution is always best.”

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But is this really true? Is simplicity always best, or more true, than any other option? Well, not only is that not necessarily the case, but it’s not even what Mr Of Ockham ever really said. So let’s take a little look at what the famous razor really does – and doesn’t – say, and what that means for our critical thinking in the modern world.

What is Ockham’s razor?

William of Ockham may not have invented this philosophical idea, but he definitely made use of it throughout his writings. 

One thing he never said, however, was “the simplest explanation is usually right”. That’s partly because, it being the early 14th century at the time, he wrote in Latin – but it’s also because, frankly, that wasn’t what he was going for.

“Occam's razor is used as a heuristic, or ‘rule of thumb’ to guide scientists in developing theoretical models,” explained Susan Borowski in an article for the American Association for the Advancement of Science. “The term 'razor' refers to the ‘shaving away’ of unnecessary assumptions when distinguishing between two theories.”

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In fact, Ockham laid out his principle like this: Numquam ponenda est pluralitas sine necessitate – that is, “plurality must never be posited without necessity”. It’s a small difference in meaning, but an important one – and it mostly comes down to that last word: necessity.

“Very often the simplest hypothesis is too simple,” Elliott Sober, a professor of philosophy at the University of Wisconsin-Madison and author of the book ‘Ockham's Razors: A User's Manual’, told Live Science. “The simplicity of a hypothesis is one consideration, among others that are relevant to assessing whether a hypothesis is true.”

Take coding, for example. You’d probably agree that this:

Python script for "hello world"
Simple. Image Credit: IFLScience


Is simpler than this:

A python script to draw a plot of x = 4 + 2sin(2x)
Complex. Image Credit: IFLScience, code from  MatPlotLib


But is it better? Well, not if your goal is to draw a graph of the function y = 4 + 2sin(2x). In that case, it’s necessary to involve extra detail and terms – even though it makes the program look more complex.

Is Ockham’s razor always true?

Even when used correctly, the principle that simple equals better doesn’t necessarily hold true in the modern world. Francis Crick, one of the discoverers of the structure of DNA, famously cautioned against its use in biology, for example, calling it “very rash to use simplicity and elegance as a guide in biological research.”

That’s true in many areas of science. Machine learning, for example, confounds the principle: “in model ensembles, deep learning, et cetera – it's usually the most complex approach that's right,” Pedro Domingo, professor emeritus of computer science and engineering at the University of Washington in Seattle, told Live Science. “And that's not surprising; the phenomena we're modeling are almost always more complex than the models, and the closer to their true complexity we can get, the more accurate the models.”

In fact, using Ockham’s razor perfectly in any scientific field can be pretty difficult. Modern science is very rarely in the position of having two competing hypotheses – one simpler, one more complex – which nevertheless predict identical results. Even if it were, it bears repeating: Ockham’s razor proves nothing – it can only act as a guide as to which hypothesis is more likely.

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“While Occam's razor is a useful tool, it has been known to obstruct scientific progress at times,” Borowski pointed out. “It was used to accept simplistic (and initially incorrect) explanations for meteorites, ball lightning, continental drift, atomic theory, and DNA as the carrier of genetic information. Once more research was done and more evidence brought to light, however, new theories emerged based on the new information.”

What does Ockham’s razor not say?

For another limitation of Ockham’s razor, we need only turn to that Most Famously Weird of subjects: quantum physics. 

As a scientific model, “quantum mechanics works exceedingly well […] but there is still no agreement on what it tells us about the fundamental fabric of reality,” science writer and journalist Philip Ball explained in The Atlantic back in 2016.

“The theory predicts not what will happen in a quantum experiment or observation, but only what the probabilities of the various outcomes are,” he wrote. “Yet in practice we see just a single outcome.”

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But what happens to change a superposition of probabilities into one observable outcome? The answer is: nobody knows. There are competing theories, sure: some say it’s due to wavefunction collapse, while others prefer the many-worlds theory – but until we invent some kind of Into The Spider-Verse type universe collapser, we’re never going to know which is true.

On the face of it, this is exactly the kind of situation where Ockham’s razor would apply. The only problem? Nobody can agree on which of the two hypotheses is simpler. 

“It’s a testament to scientists’ confusion about Occam’s razor that it has been invoked both to defend and to attack the [many worlds interpretation of quantum theory],” Ball notes. “Some consider this ceaseless, bewildering proliferation of universes to be the antithesis of William of Ockham’s principle of economy." Others believe "the Many Worlds Interpretation accounts for all the observations without the added assumption of collapse of the wavefunction … [and therefore] is preferable – according to Occam’s razor – to the alternatives.”

Is Ockham’s razor ever useful?

So it may not be able to settle beef in quantum mechanics – is that such a big deal? Is Ockham’s razor really so unfit for the modern world that we should put it to bed forever?

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Well, perhaps not – just so long as you remember what the principle can, and cannot, tell you.

“Occam's razor doesn't necessarily go with the simplest theory, whether it's right or wrong; it is not an example of simplicity for simplicity's sake,” Borowski pointed out. “It merely tries to cut through the clutter to find the best theory based on the best scientific principles and knowledge at the time.”

If Ockham’s razor doesn’t seem useful, it may well be because of how it’s usually presented – that is, somewhat ironically, in overly simplified terms. The idea isn’t that “simplest is always best”, or that any complexity is bad in any idea – it’s just a reminder not to make life any more difficult than it absolutely has to be. 

After all, as Einstein himself almost said, “everything should be made as simple as possible, but no simpler.”


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