I see this term float around the internet a lot but to this day the Google definitions have done nothing but confuse me further
EDIT: OMG I didn’t expect this post to blow up in just a few hours! Thank you all for making such clear and easy to follow explanations, and thank you for the awards!
In: 12004
“You should assume the simplest solution is true.”
If the possibilities are
1. Your partner cheated on you
2. Your partner was temporarily mind controlled by aliens
Option 1 requires one assumption: Your partner was a worse person than you realized. This is an entire plausible assumption, though a heartbreaking one.
Option 2 requires a LOT of assumptions that are all ridiculous. That aliens exist, that they’re here on Earth, that we haven’t detected them (or that there’s a grand conspiracy), that mind control tech is possible, that aliens have it, that aliens have any interest in you or your partner or splitting you up for some reason, and more.
So, according to the piece of advice we call Occam’s Razor, even though there’s technically zero evidence at all that your partner *wasn’t* mind controlled by aliens, you should assume they just cheated on you. Until proven otherwise, you should assume the simplest solution is true.
If you have competing explanations for something, the one that uses the fewest assumptions should be used.
Occam’s Razor says that when trying to explain an observation, you should go with the simplest explanation first. “Simplest” usually meaning “whatever requires the fewest assumptions”.
Say you notice that the name of an old film wasn’t you remembered it being. Maybe you notice a poster for the first Avengers movie and see it’s called “Avengers Assemble”. That can’t be right, you think, you’re sure it was just called The Avengers.
Two explanations occur to you
1) you misremembered it
2) you come from another universe where it was called The Avengers and you somehow jumped dimensions
The second one requires more assumptions, namely that other universes exist and that its possible to travel between them. The first one doesn’t require any new assumptions on top of how you already understand reality, so you go with that one.
But then you gather new evidence–another poster where it was called The Avengers. So what now–your first theory now doesn’t work, so what do you do? Immediately adopt the second theory?
No, because someone suggests a different theory. The film was released under different titles in different regions, and you saw a poster made for the UK. This isn’t as simple as that first theory, but it’s still simpler than the multiverse theory, so you change to that theory. And in this case that is the actual answer.
So, it doesn’t mean “the simplest explanation is always true”, just that it’s usually an easier process of arriving at the truth if you start at the simplest answer and work up
Edit: I should add, the important part is that if you have to theories that explain observations *equally well* then you should assume the simpler is true. It does not apply when one theory explains observations better. For example, quantum mechanics is far more complicated than Newtonian mechanics, but it explains certain observations better, so Occam’s razor doesn’t apply
Occam’s razor is often misstated as “the simplest answer is the correct one,” but it should more accurately be “the simplest answer is the best starting point to investigate.” The idea is that the more different variables or assumptions have to add up to get to a solution, the more difficult it is to investigate, and the less likely it is to occur in general. “Entities should not be multiplied beyond necessity.” is the classical way to state it.
So the classic example is: you hear hoofbeats outside, is it a horse or a zebra? Well unless you live in the African savannah, it’s very unlikely to be a zebra. We’d need more assumptions to get there – a zebra was imported to a local zoo, it escaped captivity, and now it’s running amok. Whereas a horse requires just one assumption – a horse is nearby. That doesn’t mean that it *cannot* be a zebra, it just means that you should start at “it’s probably a horse” and investigate from there.
I had a fun moment the other day, when I went to my kitchen and saw a jar of pickles left out on the counter. I knew it wasn’t me, which left two possibilities that my brain somehow jumped to:
1. A burglar broke in, stole several other items, and *also* ate a pickle. He left the jar out to taunt me.
2. My wife had a pickle and then forgot to put away the jar.
I could have totally checked my locks, made sure my valuables were still in the right place, etc. Instead I just yelled “Hey, did you leave this pickle jar out?” and got the simpler answer right away. Starting with the simpler solution (fewer assumptions than my burglar story) got me to the right answer efficiently.
EDIT: Thanks for the awards! For the dozen or so people who have commented to imply that my wife is pregnant, I just want it to be known: we are a pro-pickle family. They go perfectly next to a nice sandwich for lunch, or diced up in a tuna salad. Jars of pickles go reasonably fast in this household, no cause for alarm.
Original statement: “Do not multiply entities beyond necessity”
Rephrased in ELI5 terms: When trying to think of an explanation for something unknown, generally it’s good if your theory does not assume a large number of different factors or parameters.
Common usage: The simplest explanation is the best.
Example: If you’re a doctor trying to come up with an explanation for a patient’s symptoms, you may be able to think of two different illnesses that, when combined, account for all symptoms. After some more thinking, you can also think of a single, different illness that could explain all the symptoms. Occam’s razor suggests that the single illness explanation is the better one.
Important caveat: This is just a guiding principle, not a hard rule. Sometimes the patient really does have two different illnesses…
A razor is a fancy way of saying “rule of thumb”. To be more precise, it means that in absence of any other evidence to guide you, remember principle x.
Occam’s razor – assume the simplest explanation as most likely.
Hanlon’s razor – Never attribute to malice what can be adequately explained by stupidity.
If Theseus’ father followed Occam’s razor, he would have concluded that his son had simply forgotten to put the proper color sail on his ship and would not have killed himself.
A lot of people frame it like “the simplest solution tends to be true.” imo this is less than ideal because then you have to explain what “simple” means.
“Aliens made the crop circles” is a simple sentence but it is not at all a simple explanation.
A better way to frame O.R. is to say “the explanation that requires the least amount of assumptions tends to be correct.”
A lot of great answers in here, but I wanted to specifically explain why it’s called a “razor”, which is a bit of an odd term. It’s because it’s a methodology that is used to “cut away” unlikely hypotheses and pare things down to just the good ones.
If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.
The simplest answer is the most *likely* answer.
As an example – when looking at the orbits of the planets from the view of Earth – the counter-intuitive *simplest* answer was that we are the center of the universe and all in the heavens rotates around us. Right? It wasn’t DUMB to conclude this. From our vantage point on Earth – it *appears* so.
But, on careful study – the planets (which means “wanderers” do not orbit around us.
In order to compensate for the apparent wandering orbit of the planets around Earth, early astronomers came up with increasing complex models that had the planets doing little loops and pirouettes in the sky in order to explain why they sometimes changed direction and became “unpredictable.”
In that case though – the more complex the models became, the more problems they introduced.
The actual SIMPLEST solution was “the Earth is not the center of the Universe.”
Once you put the sun at the center of the solar system, the stars outside of it, and the planets in their proper order around the sun – everything falls into place and the models start to work flawlessly.
And though the rejection of this idea is often chalked up to religious dogma – part of it was that it disputed the status quo/conventional wisdom of the time. It asked people to reject what they were certain of and think outside the box of what they thought they knew. People get into mental “sunk costs” that cause them to double down on bad ideas rather than determine that maybe they have to start over from scratch. Whenever you hear someone assert modern science as an absolute authority on a matter – remind yourself of this. Just because everyone in a scientific field of study *agrees* on an issue, does not mean their belief is accurate. Likely the most recent high profile example was dinosaurs as cold blooded relatives of lizards vs. warm blooded relatives of birds. This idea met with fierce opposition when it was first proposed – and that early dismissal was never really acknowledged when they discovered fossils with FEATHERS in China shortly thereafter.
Science is not static. It is not irrefutable. It is not infallible. But often, if you find that you have to make increasingly complex, post-hoc adjustments to your hypothesis in order to make it work – if it is becoming increasingly complicated – you are probably headed down the wrong path. That is Occam’s razor. The more increasing complexity involved in making your guess fit, the less likely your guess is to be right.
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