Occam's Razor

Occam’s Razor is the principle that when you have two or more competing explanations for the same phenomenon, you should prefer the one that makes the fewest assumptions. It does not say the simplest explanation is always correct. It says the simplest explanation is the best starting point - and that you should not multiply assumptions beyond what is necessary to explain the evidence. The razor exists partly as a counterweight to complexity bias - the cognitive pull toward elaborate explanations even when a simpler one fits the facts.

The principle is named after William of Ockham, a fourteenth-century English friar and philosopher, though he never actually phrased it as a “razor.” The metaphor of shaving comes from the idea of cutting away unnecessary elements from an argument. The Latin formulation often attributed to him - entia non sunt multiplicanda praeter necessitatem (entities should not be multiplied beyond necessity) - captures the spirit perfectly, even if the exact words came later.

What Occam’s Razor means

At its core, Occam’s Razor is a rule of thumb about assumptions. Every explanation for anything rests on a set of assumptions - things that must be true for the explanation to hold. The more assumptions an explanation requires, the more opportunities there are for one of those assumptions to be wrong, and the less likely the overall explanation becomes.

Simplicity versus simplism

A critical distinction: Occam’s Razor favours the explanation with the fewest unnecessary assumptions. It does not favour the explanation that is easiest to understand or the one with the fewest words. A genuinely complex phenomenon sometimes requires a complex explanation, and in those cases, oversimplifying would violate the razor rather than honour it.

For example, the movement of the planets is genuinely complex. An explanation involving gravity, orbital mechanics, and the mass of celestial bodies is complicated but necessary - each element is doing real explanatory work. An alternative explanation that invokes invisible celestial beings pushing the planets around would be simpler in one sense (one mechanism instead of several) but would actually add a massive unsupported assumption. Occam’s Razor cuts the angels, not the physics. It is also distinct from the argument from ignorance: preferring the simplest adequate explanation is not the same as treating the absence of a disproof as proof of a claim.

This distinction is important because Occam’s Razor is frequently misused to dismiss explanations that are complex but well-evidenced. The razor does not say “always pick the shortest answer.” It says “don’t add assumptions you don’t need.”

How Occam’s Razor works in everyday decisions

You do not need to be a medieval philosopher to use Occam’s Razor. It is one of the most practical thinking tools you can carry.

Diagnosing problems

Your laptop will not turn on. Possible explanations include: the battery is dead, the charger is broken, a cosmic ray has corrupted the BIOS, or someone has hacked your machine remotely and disabled the power system. Occam’s Razor tells you to check the battery and charger first - not because the other explanations are impossible, but because they require far more assumptions.

The same logic applies to interpersonal problems. Your friend has not replied to your message for two days. Explanation A: they are busy, distracted, or forgot. Explanation B: they are angry with you for something you said three weeks ago, have been discussing it with mutual friends, and have decided to punish you with silence. Hanlon’s Razor would agree with Occam’s here - start with the simpler, less dramatic explanation and only escalate if the evidence demands it.

Evaluating claims and news stories

Occam’s Razor is particularly useful when assessing claims you encounter in the media or online. When someone presents an elaborate theory about why something happened, ask yourself: how many things have to be independently true for this explanation to work? How does that compare to a more straightforward reading of the same events?

This is not about dismissing everything complex. It is about noticing when complexity is doing genuine explanatory work and when it is being used to make a weak argument seem more impressive. Conspiracy theories often rely on the latter - they pile assumption upon assumption, creating an edifice that feels convincing through sheer intricacy, even though each additional assumption makes the overall theory less likely, not more.

Occam’s Razor and conspiracy thinking

The relationship between Occam’s Razor and conspiracy theories deserves special attention, because it is one of the areas where the razor is most urgently needed - and most frequently abandoned.

Why complex explanations feel compelling

There is a psychological reason why people sometimes prefer complex, assumption-heavy explanations over simple ones: complex explanations can be more emotionally satisfying. A world in which powerful hidden forces are orchestrating events feels more ordered - even more comforting - than a world in which bad things happen because of mundane causes like incompetence, coincidence, or poorly designed systems.

This connects to confirmation bias. Once someone has committed to a complex explanation, they start noticing evidence that supports it and ignoring evidence that contradicts it. Each new piece of “evidence” makes the theory feel more robust, even though the theory’s reliance on an ever-growing number of assumptions should make it less credible, not more.

Applying the razor to extraordinary claims

Occam’s Razor does not prove that conspiracies never happen - they clearly do, and history is full of documented examples. What the razor does is set a sensible evidential bar. If the simple explanation (cock-up, coincidence, structural incentives) fits the evidence, you should not leap to the complex explanation (coordinated secret plot involving hundreds of people, none of whom ever talk) without strong evidence that the simple version falls short.

The razor asks: which explanation requires me to assume the least? The answer is not always the one that feels most satisfying. That is precisely why it is useful.

Occam’s Razor in science and medicine

The principle of parsimony - another name for Occam’s Razor - has been a foundational guideline in scientific reasoning for centuries.

How scientists use the razor

In science, when two theories explain the same set of observations equally well, the simpler theory is preferred. This is not because nature is inherently simple (it often is not), but because simpler theories are easier to test and harder to defend dishonestly. A theory with many free parameters can be bent to fit almost any data, which makes it less useful as a tool for understanding the world.

Albert Einstein reportedly paraphrased the principle as: “Everything should be made as simple as possible, but not simpler.” That second clause is essential. Occam’s Razor is a tool for avoiding unnecessary complexity, not a licence to ignore genuine complexity.

Medical diagnosis and Occam’s Razor

In medicine, a related principle called “diagnostic parsimony” suggests that clinicians should try to explain a patient’s symptoms with a single underlying condition before assuming multiple simultaneous conditions. If a patient presents with fatigue, weight loss, and joint pain, a single diagnosis that explains all three is preferred over three separate diagnoses, at least as a starting point.

This does not mean patients never have multiple conditions - they clearly do, especially as they age. But the principle ensures that clinicians consider the most efficient explanation first and only add complexity when the evidence requires it.

Common mistakes with Occam’s Razor

The razor is widely known but frequently misapplied. Understanding the common errors helps you use it well.

Confusing simplicity with familiarity

People sometimes invoke Occam’s Razor to defend an explanation that is familiar rather than simple. The explanation you grew up with, or the one your social group believes, can feel simple even if it actually rests on a large number of assumptions - you have just stopped noticing them because they are so embedded in your worldview.

This is closely related to the availability heuristic. Explanations that come to mind easily feel more natural and therefore more parsimonious, even when they are not. True application of Occam’s Razor requires you to count assumptions honestly, not just go with whatever feels most intuitive.

Using the razor to avoid investigation

Occam’s Razor tells you where to start, not where to stop. The simplest explanation is the best first hypothesis, but if the evidence does not support it, you must move on to more complex ones. Using the razor to shut down inquiry - “the simple answer is obviously right, so stop asking questions” - is an abuse of the principle.

Good thinking requires holding two things at once: a preference for simplicity and a willingness to accept complexity when the evidence demands it. The razor is a starting gate, not a finish line.

Ignoring the “equally well” condition

Occam’s Razor applies when two explanations account for the same evidence equally well. If the simpler explanation leaves important evidence unexplained, it does not get to win on simplicity alone. The criterion is not “which has fewer assumptions?” in isolation - it is “which has fewer assumptions while still explaining what we observe?”

Occam’s Razor alongside other mental models

Occam’s Razor works well in combination with other thinking tools. First principles thinking shares its preference for stripping problems down to fundamentals. Probabilistic thinking provides the mathematical backbone - simpler theories tend to have higher prior probability because they depend on fewer independent conditions all being true simultaneously.

Hanlon’s Razor applies the same parsimony principle to human motives. Where Occam’s Razor says “do not multiply assumptions in your explanations,” Hanlon’s Razor says “do not multiply assumptions about people’s intentions.” Both push you toward the same discipline: resist the urge to add complexity that the evidence does not demand.

And confirmation bias explains why Occam’s Razor is so hard to follow consistently. Once you have fallen in love with a complex theory - whether it is about world events, a colleague’s behaviour, or your own life story - the simple alternative feels boring, unsatisfying, and somehow less true. The razor is a correction for this very human tendency to mistake intricacy for insight.

In a world that rewards complexity, hot takes, and elaborate narratives, the discipline of asking “but what if it’s just the simple thing?” is quietly radical.