Summary: The fundamental question of rationality is, why do you believe what you believe? In this exercise, we ask that question repeatedly in an attempt to figure out our foundations.

Tags: Repeatable, small, experimental

Purpose: The purpose is twofold. Firstly, we want to grow comfortable and familiar with figuring out where our beliefs come from. Second, we want to do some sleuthing around beliefs we maybe aren’t sure about.

Materials: Paper and pencils are useful. A device capable of accessing wikipedia is invaluable.

Announcement Text: “I ask you the fundamental question of rationality: Why do you believe what you believe?”

There are lots of things we think are true. Many of them are actually true! In this meetup, we’re going to state some beliefs about the world and then step through why we hold that this is true – or if we disagree, why we hold that this is false! We’ll list our reasons, and then consider whether those reasons are credible. The intention is to practice on easy targets, but that doesn’t mean that the easy answers of “well everyone knows that” or “its obvious” are going to pass!


1. As the organizer, state a fact about the world. Examples include “The moon is made of blue cheese.” “The earth is basically a sphere.” “Cars run on faerie power.” “Things fall downwards because of gravity, which accelerates objects at about 9.81 m/s^2.” “I am Abraham Lincoln.” “Humans take oxygen from every inhalation and exhale carbon dioxide.” Mathematical nerd-sniping can be good too if you have a group that will enjoy it.

2. Next, each person writes down why they believe the fact to be true or false. This may be “because I did this experiment myself” or “because these people told me” or something else. You can write down more than one reason! Once you’re done, find a partner. 

3. With your partner, take turns trying to poke holes in each other’s reasons. (“Maybe the experimental evidence provides an alternate explanation, like X.” “Maybe the person who told you that isn’t really that trustworthy.”) Write down the possible holes. For each reason with holes, repeat step two, writing down why this hole doesn’t convince you or why it does convince you this isn’t a good reason.

4. When you and your partner are satisfied, go to step 1 with a different fact.

There isn’t a way to lose Why Do We Believe. If you ever realize that you are wrong, you instantly change sides to the ‘winning’ team with the truth. However, you can still strive to play well! Come up with the strongest possible reasons, and the strongest possible holes in your evidence.

If you want to win bonus points however, go out and perform an experiment. It doesn’t need to be a big official experiment to count!


Setting yourself up somewhere with more space to move about and more materials designed for replicating physics experiments sounds like fun. Someday I want to run a "So you think the world is flat? Let's prove it!" meetup because playing with lasers and sundials sounds like a good summer evening. The glaring flaw here is that seeing the physics experiment with their own eyes might not be the key reason someone thinks this might be wrong. 

If your group has a common interest other than rationality, that interest is a good source of facts. Investigate how best to draw perspective correctly, how best to make a magic deck curve out in monoblack, or what the effective distance of a hockey slapshot actually is.

Hardmode: make the fact a controversial one, where there is genuine uncertainty in your own heart and people are likely to have assumptions about the answer. I recommend against doing this as your first few examples, possibly not on the first time you run this. In a martial arts class you do not start to learn a new technique by sparring with it.

Notes: Try not to drive the reasons people come up with. You might expect certain answers, and it’s cool to anticipate the test someone will want to run so you can have supplies ready, but there’s no point testing reasons that nobody objects to. 

Timing can vary wildly. If it is much too short (say, less than two minutes) that’s a sign people might want to try harder with poking holes in reasons. Still, “I believe it because everyone around me says its true” can be an honest answer and that doesn’t take long to resolve. You care more about getting the answers people actually believe than you care if those are good reasons or not. If people are excited about a chain of evidence or have dived into devising an experiment, that’s great! Don’t feel like the whole group has to stay on the same questions at the same time.

Credits: Recommended reading is Scientific, Legal, and Rational evidence and Fake Explanations but honestly this is an outgrowth of “what do you think you know and how do you think you know it?” all of which I got from Eliezer Yudkowsky.

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3 comments, sorted by Click to highlight new comments since: Today at 4:02 PM

We ran this in Freiburg, Germany.

It worked very well! 11 people came and it was suitable for that group size. I made some small changes.

I started with steps 1 - 3 as described above. People had 5 minutes to come up with the reasons why they (dis-)believed the statement ("The earth is a flat disk") and then 10 minutes to poke holes (5 minutes per partner).

Then we came back to a big circle and ensured everything was clear. I then projected a list of statements onto the wall and gave each person 5 minutes to choose one statement and come up with reasons for (dis-)believing. I explained that making any assumptions or having only a certain degree of conviction was perfectly fine (e.g. I am 60% certain that capitalism has a net positive effect on the world), they should just make that clear to their partner later. Some people struggled making a choice so I offered to choose for them, which they accepted (so having some mechanism for assigning statements at random may be valuable).

Then people split again into (different!) pairs and had 15 minutes (7.5 minutes per person) to poke holes in each other's reasoning. For the most part people randomly chose different statements from their partner, which made the exercise more interesting because you had to poke holes into something that you hadn't thought about much yourself. Funnily, in one case, a pair chose the same statement but had opposing opinions on it.

We repeated it two more times with new statements and new partners.

The list of statements I projected onto the wall. Note that I don't necessarily endorse any of these statements as they are here listed. They are intentionally meant to be though provoking and controversial.

Many people preferred the more controversial statements at the bottom.


  • Earth is a flat disk.
  • The moon is made of cheese.
  • Humans have walked on the moon.
  • COVID is a dangerous disease that killed many people.
  • Vaccines cause autism.
  • Things fall because of gravity, which accelerates objects at 9.8 m/s^2
  • Humans use only 10% of their brain.
  • Humans are the most intelligent in the animal kingdom because they have the biggest total brain size.
  • The scientific method is the most effective way of achieving knowledge about the world and the universe.
  • Seeds are the spicy part of chili peppers.
  • Microwave ovens heat food from the inside out.
  • (Biological) evolution necessarily causes organisms to evolve from less complex to more complex.
  • Glass is a high-viscosity liquid at room temperature (e.g. old cathedral windows are thicker at the bottom)
  • Muscle soreness after exercising is caused by lactic acid.
  • Rusty metal can cause tetanus infections.
  • Cold temperatures in winter can cause people to catch a cold.
  • 0.999.... is the same as 1
  • Human beings have five senses.


  • Artificial Intelligence very seriously risks extinguishing all human life within the next 30 years.
  • Capitalism has a net positive effect on the world.
  • Colonialism had a net positive effect on the ex-colonies.
  • Open borders (no travel restrictions between countries) would have a net positive effect on the world.
  • Human beings are intrinsically more valuable than plants or animals.
  • Spending significant taxpayer resources (e.g. $1 million) to save five people lost in a submarine has a net positive effect on the world.
  • Investing significant resources (e.g. $1 million / year) to fight the extinction of animals such as the Sumatran rhinoceros (~ 80 left in existence) has a net positive effect on the world.
  • God exists.
  • Religion has a net positive effect on the world.
  • Gender is (almost) entirely a social construct.
  • Nuclear energy has a net positive effect on the world.
  • Every controversial topic should be publicly debated instead of censored.
  • Liberal democracy is the form of government with the highest net positive effect on the world.
  • Voting in national elections is a duty for the individual.
  • If a foreign nation starts a military invasion of your home country you have a moral duty to take up arms.
  • Objective reality exists.

I'm glad it worked well for you! Thanks for the extra data points :)

"Organizer's choice" seems like a fine way to help people decide what belief to explore. "Roll a die, count down from the top" seems also reasonable.

How did your time limits work? I often put timers in meetups to keep things moving, and find people almost always want more time.

I am not surprised people preferred the controversial beliefs. I don't have a big list of options yet, but I sort by directness instead of controversy. “Cars run on faerie power" is direct, because you can flip up the hood on a car and have someone start it plus often people have some memories of being told how cars work. Look, no faeries. "Humans take oxygen from every inhalation and exhale carbon dioxide" is less direct, because you have to get kind of clever to test it and lots of people don't quite remember learning it but suspect they heard it in a class maybe.

Did any of the controversial pairs get heated? Did it seem like they built as solid maps of where their beliefs come from as the non-controversial sets? The thing I'm worried about (and the source of the suggestion not to do controversial topics early) is people searching for reasons they think are respectable, not things they have as cruxes.

I think in many cases people would have been happy to continue after the timers were done. There was no really heated interaction and I assume it was also because of the time limit. The results would probably look different (better?) with more time.

The thing I'm worried about (and the source of the suggestion not to do controversial topics early) is people searching for reasons they think are respectable, not things they have as cruxes.

Sounds plausible. We did not really try to dig into that.

I would like to repeat the event in the future and maybe I'll introduce some variation to figure some of these questions out :-)