Occam’s Razor is a philosophical principle that says in situations where there are competing explanations, we should prefer the simplest explanation since it’s most likely to be the correct one.
Occam’s Razor gets its name from the English Franciscan Friar, philosopher and theologian, William of Ockham; though the idea of Occam’s Razor dates way back to Aristotle.
“Entities should not be multiplied without necessity”, is how William of Ockham fashioned the phrase and is the principle of Occam’s Razor. In plain terms, when we have more than one explanation or hypothesis available, we should choose the one that makes the fewest assumptions since that option is the most likely to be correct.
Occam’s Razor Examples
- When you hear hoofbeats, think horses, not zebras.
- If an ant draws a picture in the sand, it probably was a coincidence. Ants can’t draw.
- If a tarot card reader gives an accurate reading, it’s probably luck and skill, not a supernatural force.
- If you hear loud bangs on independence day, it’s probably fireworks.
- If your husband is late to get home, he’s probably stuck in traffic.
Explanations and More Examples
1. “Think Horses, Not Zebras.”
“When you hear hoofbeats, think of horses, not zebras” is an aphorism coined by Dr. Theodore Woodward from the University of Maryland.
This saying is taught in medical schools and is considered a medical proverb; though the phrase accurately captures Occam’s Razor.
When diagnosing a patient, doctors should look first at the expected causes of an ailment first, rather than its unlikely or ‘exotic’ causes. This is because the likeliest explanation is probably the correct one.
2. An Ant Draws a Line in the Sand
If an ant draws a picture in the sand, don’t overthink it. The most obvious answer is that it’s a complete fluke. Ants can’t draw.
Hilary Putnam was an American philosopher and mathematician whose work greatly influenced the philosophy of mind. In Putnam’s essay, “A Brain in a Vat”, he discusses the problems with Cartesian skepticism and particularly the concerns with the thought experiment in question: A Brain in a Vat.
Putnam starts the essay with a different, lesser-known thought experiment:
“An ant is crawling on a patch of sand. As it crawls, it traces a line in the sand. By pure chance, the line that it traces curves and recrosses itself in such a way that it ends up looking like a recognizable caricature of Winston Churchill. Has the ant traced a picture of Winston Churchill, a picture that depicts Churchill?”
Putnam was a proponent of Occam’s Razor, or we can strongly suspect he was based on the above thought experiment. The essay critiques Cartesian skepticism, and in so doing tells us to be reasonable in our thinking.
That is, the ant we (we suspect) had no intention of drawing Churchill or drawing anything at all. That’s because it’s an ant. Maybe we underestimate the intelligence of ants, and the ant had seen an image of Churchill and set out to draw him in the sand.
Occam’s Razor says this would be a leap in thinking because it assumes too much when there are simpler explanations available.
3. My Dog Ate My Homework
If a student says that a dog ate their homework, the most logical assumption is that the student just didn’t do their homework.
‘My dog ate my homework’ has become the default expression for a glib and poorly thought-out excuse for not turning in an assignment on time.
Teachers are told endless excuses for students not completing their homework on time. It could be true that the dog did in fact eat the student’s homework; however, that explanation is less likely than the alternative explanation, being that the student just didn’t finish their work on time.
Of the competing explanations, the one that is most reasonable (makes fewer assumptions) is that the student did not finish their homework on time, and so Occam’s Razor prefers this explanation.
4. Waiting on a Text
Scenario: Ashley and Mike just started dating. Both are quick to respond to each other’s texts, but one day Mike texts Ashley, and she doesn’t respond immediately. This strikes Mike as unusual, and he starts wondering different explanations for why she hasn’t texted him back yet.
Mike starts hypothesizing that Ashley is no longer interested, maybe she met someone else or maybe he did something to upset her. What doesn’t occur to Mike is that maybe she just hasn’t had a chance to check her phone and that it’s been a busier day for her than usual.
Occam’s Razor says we should assume the likeliest explanation; which, in this case, the likeliest explanation would be that Ashley hasn’t had a chance to respond to Mike’s text, and so that is why she hasn’t responded.
5. Getting Home from Work Late
Scenario: Emily’s husband normally comes home from work at 6 in the evening. It’s now past 8, and he still isn’t home. He hasn’t called or texted to let her know, and so Emily starts to worry that he got into a car accident.
This situation is common, and while car accidents happen, there are other explanations that would apply in this situation that makes fewer assumptions. For example, it’s possible he got caught up at work and had to stay late, or that traffic on his way home was terrible.
These explanations make fewer assumptions, and so Occam’s Razor would endorse either as a plausible explanation for his getting home late.
6. Failing a Test
Scenario: Ben just got back his English test and is shocked to discover that he failed. He tells his parents that his teacher failed him on purpose because she has it out to get him and doesn’t want him to succeed in life.
Ben’s parents are not so easily fooled. They realize what most likely occurred is Ben wasn’t prepared for the test, which is why he failed.
Despite not realizing it, Ben’s parents are applying Occam’s Razor to identify the simplest explanation for why Ben failed the test.
7. Stolen Cookies from the Cookie Jar
Scenario: Jack looks in the cookie jar only to find it empty. It’s possible a robber broke into his house last night and stole the cookies; however, what most likely occurred is that his son snuck downstairs at night and took the cookies from the cookie jar.
Jack doesn’t know for a fact that this son did take the cookies until he confirms that this is what happened. Still, he strongly suspects that of the explanations available, that his son took the cookies makes the most sense.
Though Jack probably doesn’t realize it, he is using the rationale of Occam’s Razor to form his hypothesis on why the cookies are gone.
8. My Car Won’t Start
Scenario: Jen is getting ready to go to work. She gets in her car and turns the ignition but her car won’t start. Jen thinks of explanations for why her car isn’t starting and concludes that the car battery must be dead.
Jen could have suspected her neighbor of having tinkered with her car, or maybe the government is conducting a social experiment and collecting data on how people react to their car’s not working.
These other hypotheses are much less plausible than the most obvious explanation, being that her car battery is just dead. Jen assumes that this is the correct explanation and in this way uses the logic illustrated by Occam’s Razor.
9. A Bad Headache
Scenario: Mary has a headache and starts to google what might be the cause. She googles her symptoms and starts to worry that she has a brain tumor and that’s what’s causing the headache.
Unfortunately, Mary got carried away googling her symptoms and fell down the internet rabbit hole of discovering new and likely inaccurate self-diagnosis. Headaches occur for all kinds of reasons: sleep deprivation, dehydration, stress, and so on.
By googling her symptoms, Mary loses sight of what the most reasonable explanation is for her headache. Occam’s Razor would tell her that she just has a headache.
10. Flat Tire
Scenario: Chris has a flat tire. He thinks about how this could’ve happened and suspects someone from his past that he had a falling out with. Chris assumes that the person tracked him down and slashed his tires.
It’s possible that someone has a personal vendetta against him, and that this person tracked him down and did in fact slash his tires. However, what is more reasonable, and what Occam’s Razor would endorse is his tire is flat because it probably ran over a sharp object or nail that punctured the tire.
11. Misplaced Wallet
Scenario: Andrew misplaced his wallet. He’s looked all over his house and can’t seem to find it anywhere. He considers a few possible explanations for how his wallet went missing and concludes that his cleaning lady stole it. He later finds his wallet sitting underneath the seat of his car.
If Andrew knew the principle of Occam’s Razor, he may not have accused his cleaning lady of having stolen his wallet in the first place. Occam’s Razor would suggest that the most likely explanation would be that he simply misplaced his wallet. Any other explanation involves further assumptions or more assumptions than is necessary given the situation.
12. A Loud Thud
Scenario: Sally hears a loud thud coming from outside. She’s not sure what it could be and considers various options. She thinks it was the sound of a gunshot. Sally lives in the US, but she’s not American and forgot to check the date. Turns out, it’s July 4th which is America’s Independence Day. The loud thuds were the sounds of fireworks.
If Sally knew it was July 4th, she would have been quicker to realize what the sound was. Since she forgot the date, she was unable to arrive at the correct conclusion and assumed more than what was necessary (in terms of an adequate explanation for the sound.)
13. Flu-Like Symptoms
Scenario: Liz visits the doctor because she’s having several flu-like symptoms. She has a fever, chills, body aches and pains and a headache. The doctor tells her that there’s nothing he can do for her, it’s a common flu and the only thing she should do is rest. The doctor did not run any further tests to see whether something else might be occurring. Had he run tests, he would have discovered that Liz has Lyme Disease, and that’s why she is experiencing flu-like symptoms.
This is the thing with Occam’s Razor—it’s not foolproof. Occam’s Razor can result in the wrong answer, as we’ve seen with this example where the doctor jumped to the wrong conclusion. The principle is meant as a general rule of thumb when sorting through various hypotheses and acts as a guide to rational thought processes.
14. Grading Student Essays
Scenario: A professor is grading exams for the philosophy course she teaches. She comes across two exams written by separate students that are extremely similar to each other. The professor asks both students to meet since she suspects them of having cheated on the exam. Both students say that they didn’t cheat, and it’s just a coincidence that their exams are the same.
The explanation the students offer is possible—perhaps they didn’t cheat and their exams are just extremely similar. The professor is not so gullible and has dealt with students cheating many times in the past, so while she would like to believe them, she ends up resorting to the most plausible explanation: the students were cheating during the exam, and that’s why the tests are the same.
15. Daytime Sleepiness
Scenario: Roger gets hypersomnia, which is described as excessive daytime sleepiness and constantly feeling the need to take a nap. Roger’s wife thinks he has Sleep Apnea, because he wakes himself up from snoring, though he doesn’t realize it. Roger doesn’t think he has sleep apnea and assumes that he’s tired during the day because he works too hard.
If Roger listened to his wife, he would learn that hypersomnia is a symptom of sleep apnea and that this is a common problem people face. While Roger’s wife did not realize she employed the logic of Occam’s Razor, this is nevertheless the mode of thinking she used to form her explanation of why Roger is so tired all the time.
Occam’s razor is one of the most common heuristics. It is a mental shortcut that reminds us that, sometimes, the simple answer is the correct answer. In fact, statistically, it makes sense to take the path that has least variables, because there are less opportunities to make a logical mistake! However, this heuristic can cause us to make incorrect assumptions a lot of the time. Like all heuristics, it’s valuable but imperfect.