Occam’s Razor

The Basic Idea

Imagine you have plans with your friend to go grab a drink after work. A couple of hours before, you get one of the following texts:

Text A: Sorry to do this, but my stomach is feeling weird and I have a bit of a fever and don’t think I’m up for a drink. I also think I’ll be staying at the office later than expected because I was just assigned to this huge project. My grandma also hasn’t been doing so well recently so if I do have spare time I should go check in on her. Can we reschedule drinks?

Text B: Hey, my stomach is feeling a little weird. Can we reschedule drinks?

Despite the fact that Text A has more precise details, we are likely to feel annoyed by the overwhelming amount of information and excuses our friend is presenting. Text B is a simple explanation and gets straight to the point, making us more likely to believe and accept it.

It turns out, even when it comes to more complex matters – like scientific theories or philosophical dilemmas – we tend to favor the simple explanation over the complicated one. This rule of thumb is known as Occam’s razor, and helps us eliminate overly elaborate theories as they are impenetrable and hard to prove or disprove.1 However, it is important to note that favoring the simpler explanation does not mean it is true. It is simply a heuristic that helps guide philosophers, scientists and policymakers on how best to approach a phenomenon.

You gave too much rein to your imagination. Imagination is a good servant, and a bad master. The simplest explanation is always the most likely.

– Agatha Christie, in her detective novel, The Mysterious Affair at Styles2

Key Terms

Razor: philosophical ‘razors’ are principles or rules of thumb that allow us to ‘shave off’ unlikely explanations for a phenomenon. They are mental tricks that aren’t right 100% of the time but often enough that they are worth using.3

Heuristic: mental shortcuts that help us make judgments of probabilities. Depending on the context, heuristics can help or hinder our decision-making.

Ad Hoc Hypothesis: hypotheses or assumptions added to an ‘old theory’ to prevent the theory from being thrown out due to new conflicting evidence. Ad hoc hypotheses unnecessarily complicate theories and are discarded according to Occam’s razor. 4

Nominalism: a philosophical theory that suggests reality is only made up of particular items, not of general entities.5 It boils down generalities to their simpler items and therefore, philosophers that are nominalists often employ Occam’s razor.

Occam’s Duct Tape: the opposite of Occam’s razor: an approach to problems with an absurd number of assumptions.3

Parsimony: the quality of being frugal with explanations. It suggests that ideas are usually connected in the simplest or most economically sound way possible.


Occam’s razor can be boiled down to the concept that it’s best to keep things simple. This rule of thumb has been employed throughout history, with many philosophers and scientists agreeing that, all other things being equal, the simpler theory is better.6 Perhaps the first known statement on the matter was spoken by Aristotle, an ancient Greek philosopher, when he stated that “we may assume the superiority, ceteris paribus [all things equal], of the demonstration which derives from fewer postulates or hypotheses.6

The logic is clear: if there is a simpler, easier way to explain something, why wouldn’t we use that explanation? As Italian philosopher St. Thomas Aquinas stated, “if a thing can be done adequately by means of one, it is superfluous to do it by means of several.6

Philosophers suggested that there were two different ways to employ simplicity:

  1. syntactic simplicity, which is about limiting the number and complexity of hypotheses
  2. ontological simplicity, which is about limiting the number and complexity of things the hypothesis is said to explain.6

St. Thomas Aquinas is a philosopher whose work is most often associated with Occam’s razor. Aquinas believed that Occam’s razor helped prove the existence of God. He suggested that the simplest theory about Earth’s creation was that God created it. His theory was that what is simplest is what adheres to nature, and that since the idea of God is naturally implanted in our minds, it is the simplest explanation.7

Although many philosophists were familiar with the concept of simplicity, it is William of Ockham who is most often associated with the heuristic. William of Ockham was a prominent philosopher of the 14th century. Ockham was a nominalist, which in his case, meant that he tried to reduce his ontological categories to a bare minimum.8 William of Ockham was careful not to deny complex explanations, but merely suggested that we should suspend judgment on them. To the best of one’s ability, we should shave off any excess and keep only the bones of the theory.1

Although William of Ockham was the inspiration for the term ‘Occam’s razor,’ he did not coin the term. It was Sir William Hamilton, a Scottish metaphysician, who wrote about Ockham and first used the term ‘Occam’s razor.’9



Ray Solomonoff

American mathematician who came up with the theory of universal inductive reference. The theory is a mathematical formula of Occam’s razor and suggests that the way to determine whether something is true is to use intuition, which usually points to the simpler explanation.10

William Ockham

14th century philosopher, who, due to his method of adhering to ontological simplicity by shaving off excess proponents of a theory, became the namesake for Occam’s razor.

C. Lloyd Morgan

British psychologist who suggested that a behavioral act should not be explained in complex psychological terms if it can be explained by lower faculties of the mind. This proclamation provides support for behaviorism, which suggests that all behavior is learnt, rather than a result of innate complex neurological faculties.11


Occam’s razor is a rule-of-thumb widely used across disciplines. It can help us make decisions more efficiently, and allow us to make conclusions with limited insight or information. Occam’s razor relies on our tendency to satisfice, or operate within the confines of bounded rationality. Since our rationality is inevitably bounded by time, mental capacity and available information, we use Occam’s razor to make decisions that are “good enough.”

Occam’s razor is not only a useful tool for professionals – scientists, mathematicians, or philosophers – but for daily life as well. Using Occam’s razor, we consider the simplest explanation for an observed event and therefore are prevented from getting stuck in a whirlpool of overthinking.12 For example, if you have a headache, you can easily get caught up in the idea that the headache is a symptom of a much worse problem, like a brain tumor. If you adhere to Occam’s razor, however, you can rest assured that your headache is probably just reflective of dehydration. This is the simpler answer, and according to Occam’s razor, therefore the better one.

Occam’s razor can also be useful for debunking conspiracy theories. Consider the popular conspiracy theory that Buzz Aldrin did not actually land on the moon, because the American flag was ‘waving’. People have come up with elaborate theories suggesting that NASA fabricated the whole thing, but Aldrin explained that he was twisting the flagpole into the moon soil, which explains its movement.13 That might not be the most exciting explanation, but it is a much simpler one. Occam’s razor can help us wade out the noise and focus on the basics.

Additionally, Occam’s razor allows us to resist far-fetched or complex ideas, which also prevents us from feeling overwhelmed when we encounter a problem. It helps us break down a problem into its simplest components which can make it more manageable.


While Occam’s razor is a useful tool that screens for simplicity, there is no guarantee that because a theory is simpler, it is more accurate. The fact that the explanation is simple is not enough to prove that it is right: there must be more corroborating evidence.1 Moreover, using Occam’s razor to reject complex ideas and focus only on more simple ones can be said to be preventative of critical thinking and innovation.

Additionally, while Occam’s razor might point us to the best explanation if we have two potential theories that explain the same results, we don’t often find ourselves with two theories that predict identical results. It is likely that the theories would differ in what they are trying to explain, which means it could be difficult to judge whether one is truly simpler than the other, or just different.14

Simplicity might also hamper scientific progress. Often, new theories seem incredulous when they are first iterated because they are so far from current belief systems. People originally thought that the Earth was flat because that was what could be inferred from observation; it was the simplest answer. However, more complex understandings of the world, such as solar or lunar eclipses, suggested that the Earth must be round. For scientific paradigm shifts to occur, we actually need outlandish, creative theories that displace pervading understandings.

Occam’s razor in the Courthouse

Occam’s razor is a useful tool for defense tactics, as well as determining punishment sentences.

Criminal-defense attorney Scott Greenfield suggests that the best way to win a case is through the KISS principle: Keep it Simple, Stupid. This principle is similar to Occam’s razor. When a witness is being questioned, they can answer either by contesting, explaining or admitting to what the defense is claiming. Greenfield suggests that the best tactic is to accept the facts and keep the case as simple as possible, as when people try to ‘explain’ or ‘contest’ that they find themselves making the case more complicated than necessary and diminishing their credibility.15 As Greenfield says, “the more things you must contest and the more explanations you must provide in order to mount a defense, the more likely it is that you will be convicted.15

Occam’s razor is also a rule-of-thumb attitude for determining punishment in the judicial system. The concept of penal parsimony, which suggests that punishment that is more severe than necessary is ethically unjustifiable, functions in a similar way. The simpler sentence – just like the simpler explanation is favored by Occam’s razor – is thought to be the best one. Penal parsimony was a concept first introduced by Jeremy Bentham, an 18th century philosopher and legal reformer, who specifically mentioned Occam’s razor in his writings. The phenomenon and his work helped lead to the prison abolition movement, which seeks to reduce prison sentences.1

Occam’s razor in Patient Care

Doctors can adhere to Occam’s razor when treating their patients. Within the medical field, the heuristic suggests that doctors should look for the fewest possible number of causes to explain a patient’s symptoms. This is known as diagnostic parsimony and can reduce the chance that a practitioner over-treats their patients. This will limit unnecessary prescriptions and can help reduce a patient’s anxiety by making their situation appear more manageable.1

However, other professionals in the medical field would point to Hickam’s dictum to contradict Occam’s razor. Hickam’s dictum is the idea that “patients can have as many diseases as they damn well please.16 Statistically, it has been found that patients are actually more likely to have multiple related diseases than have one source explain all their symptoms.17 Occam’s razor might therefore make doctors over-simplify a medical problem and not treat it as required.

Related TDL Resources

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We often believe that using big words will help us sound intelligent. As a result, people consistently use jargon specific to their field to try and prove that they belong in the field. However, using uncommon words or field-specific vocabulary can make things confusing for others. In this article, our writer Preeti Kotamarthi examines why we have this obsession of using big words and why we might want to throw out that urge and keep things simple.

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  2. Occams Razor Quotes. (n.d.). Goodreads. Retrieved April 8, 2021, from https://www.goodreads.com/quotes/tag/occams-razorOR Occam’s Razor Quotes. (n.d.). AZ Quotes. Retrieved April 8, 2021, from https://www.azquotes.com/quotes/topics/occam’s-razor.html
  3. 9 Philosophical razors you need to know. (2020, September 10). Life Lessons. https://lifelessons.co/critical-thinking/philosophical-razors/#1
  4. Occam’s Razor. (2017, August 17). What is Occam’s Razor? [Video]. YouTube. https://www.youtube.com/watch?v=M5WDdvkFaDg
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  7. Aquinas, T. (2017). Question 2. The existence of God. New Advent. https://www.newadvent.org/summa/1002.htm
  8. Spade, P., & Panccio, C. (2002, August 16). William of Ockham. Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/entries/ockham/#OckhRazo
  9. Borowski, S. (2012, June 12). The origin and popular use of Occam’s razor. American Association for the Advancement of Science. https://www.aaas.org/origin-and-popular-use-occams-razor
  10. Altain, A. (2012, July 11). An Intuitive Explanation of Solomonoff Induction. LessWrong. https://www.lesswrong.com/posts/Kyc5dFDzBg4WccrbK/an-intuitive-explanation-of-solomonoff-induction
  11. B., S. (2017, February 11). Science and Behavior: Occam’s Razor. Blogs @ SCSU – Educational blogs from our community. https://blog.stcloudstate.edu/gcmertens/science-behavior/science-and-behavior-occams-razor/
  12. Occam’s Razor. (n.d.). Conceptually. Retrieved April 8, 2021, from https://conceptually.org/concepts/occams-razor
  13. The Moon Landings Were Faked. (2008, November 20). TIME. https://content.time.com/time/specials/packages/article/0,28804,1860871_1860876_1860992,00.html
  14. Ball, P. (2016, August 11). The Tyranny of Simple Explanations. The Atlantic. https://www.theatlantic.com/science/archive/2016/08/occams-razor/495332/
  15. Bennett, M. (2007, June 27). Occam’s Razor in the Criminal Courthouse. Defending People – Criminal defense and free speech. https://blog.bennettandbennett.com/2007/06/occam-razor-in-criminal-courthouse/
  16. Occam’s razor. (n.d.). Psychology Wiki. Retrieved April 8, 2021, from https://psychology.wikia.org/wiki/Occam%27s_razor

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