Spiked Math Games  // Math Fail Blog  // Gauss Facts  // Spiked Math Forums  // Spiked Math Comics

445

Three logicians walk into a bar - September 22, 2011
• Currently 4.5/5
• 1
• 2
• 3
• 4
• 5
Not sure who made this joke up... but it's a good one!!

Edit Sept 23, 2011: After reading and understanding the above, check out (x,why)'s more sophisticated version which makes for an excellent followup joke!

I'm not sure if I get it

These people are logicians. They're trying to figure out if *everyone* wants beer. Boolean logic.

The first guy wants peer but doesnt know if the other guys do. If he didn't want beer he would have said no, not everyone wants beer. Same with the second guy. Since both guys before didnt say no before the last guy, he wanted beer too, thus he was able to say yes. That probably sucks as an explanation.

that is a good explanation. its been years since I took logic...so I was trying to work it out in my head, but your explanation made perfect sense. :)

how can you tell that the first guy wanted beer? if guys 1 and 2 didn't want beer, the joke falls flat on its face. (a good joke and i really like and love it; but not foolproof).

if guys 1 and 2 didn't want beer, they would answer "no"
and "no" means "no, not everyone want beer"

they're logicans in logical quiz, so they cannot lie

ohhhhhhhhhhhhhh I see

That was actually perfect. Thank you.

If the first logician didn't want a beer, he'd know that "all logicians want a beer" is false, so he could have answered "no." Since he didn't know about the other two, he had to answer "I don't know." Likewise for the second logician: if he didn't want a beer, he'd have answered "no," but not knowing the third logician's opinion, he had to also answer "I don't know." When it comes to the third logician, he knows (based on their answers) that the first two want beers, and since he wants a beer as well, he (and only he) can be certain that "all logicians want beers" is true, making the correct response "yes."

Funniest one EVER!

LOLLOLLOLLOLLOL Morning silliness. I had to explain this to wifey. Or rather, I had to explain, why I was giggling uncontrollably.

To make it a bit more complicated:
The last one could have said "three beer please" if he didn't want a beer. (Remember that the lady on the left does want beer, and everybody knows that, otherwise they would have said no immediately.)

The way I read it, it makes sense only if the Lady is a waitress. After all, the title says "Three logicians..."

Not quite. Whether she wants a beer or not is not the issue. It is whether the logicians know whether or not she wants a beer. Them not knowing whether she wants a beer doesn't imply that she doesn't want one. They'll say 'I don't know' even if the waitress wanted a beer, because the waitress hasn't announced her preference. So the last guy, also not knowing the waitress' preference, cannot possibly order 3 beers. If only the waitress/lady said 'You guys want to join me for some beers?', your version would have worked.

Assuming that the waitress is part of the potentially beer-wanting group doesn't invalidate any of the logicians' responses. If the waitress did not want beer but was part of "everyone" then her question would be invalid because she would know the only correct answer is "no".

Wanting beer doesn't imply that you ask questions only when you don't know their answer. I want beer just about all the time. What's my name?

The problem here is that everyone is not defined propper ... ^^

Maybe the question should have been "Does anyone want a beer?"

"Do the three logicians within 10 meters of me..."

Hahahaha! Brilliant!

arghh, too difficult to me :(

Don't know who invented it, but I heard a variation of this on NPR with Will Shortz one Sunday morning a while back. Even stole it for a comic (click the link).

Ah yes, you're version is much more sophisticated! It makes for a excellent followup joke to the version I used!!

It should be "your version is much more ...." and not "you're version is much more ...." :P #grammarnazi

Yup, you're right, I was initially typing one sentence that used "you're" then switched to another sentence without change the you're to your.

There is no counterexample to a mathematician wanting beer.

I hadn't finished, you thick thick finger of mine...

The first logician knows he wants a beer but not if the other two do. The second logician knows that he and the first wants a beer but not if the third does. The third knows they all want a beer.

I want a beer...

At least they weren't waiting for a fourth logician.

That is simply awesome! Thanks for the comics.

Wait a minute...there are FOUR logicians! Not 3. Good logic, bad math. LOL

It took me a minute to get this one. Then it made me very happy :) I think I will pass it on to a friend who loves logic.

Tastes great - less NILing!

Had to read the explanation to get it. But when you do it's really a funny one :>

LOVE THIS. Only thing I don't like about it is how gendered it is. It reads to me like the only woman in there is the waitress... and the logicians are all men. (Yes, they could be short-haired women, blahblah, but to me that doesn't erase the fact that the waitress is EXPLICITLY female and the others are ambiguous. They are ambiguous, AND different from the one who is definitely a woman, AND all three the same.)

I choose to believe that you are trolling, since the alternative makes me sad

Ah, that's just a coincidence but I can make another version if you want. There's also no black people in this particular comic.

Yes no Asians either, also if you include an Asian, be careful you might just be reinforcing the stereotype that all Asians (usually of Chinese descent) are good at math. So please could all your characters be non stereotypical, so you can show how you have broad views and how socially aware you are. k thnx

Who said the girl was a waitress?

Funnily enough, they all struck me as looking female, and that was before I even read your comment. I think perhaps because they all look like they are wearing dresses (the triangular garment registers as a dress to me, and their hair and faces don't register as particularly male, so it defaults to female in my mind). Strange how differently our biases play out, isn't it?

Strictly speaking, the first two could have answered "I don't know" because they hadn't made up their minds yet.

I'm obviously not into maths! But this reminds me of the joke about how many Mennonites you should take with you on a fishing trip. The correct answer is "At least two". Because if you take one, he'll drink all your beer. If you take two, neither of them will drink any of the beer.

If guy 1 didn't want a beer he could have immediately have said "No, not everyone wants a beer!".

Not quite. Whether she wants a beer or not is not the issue. It is whether the logicians know whether or not she wants a beer. Them not knowing whether she wants a beer doesn't imply that she doesn't want one. They'll say 'I don't know' even if the waitress wanted a beer, because the waitress hasn't announced her preference. So the last guy, also not knowing the waitress' preference, cannot possibly order 3 beers. If only the waitress/lady said 'You guys want to join me for some beers?', your version would have worked.

The joke should be 3 programers walk into a bar not 3 logicians because the third person cannot conclude that the first two want beer by them not knowing if "everyone" wants beer. The fact is there exist 2 sets: set A "want beer" and set B "not want beer" and therefore AUB complement is all that is neither in A nor in B, meaning that one of the first 2 guys could have neither wanted beer nor not wanted beer, making the third guy's assumption unfounded.

Three mathematicians walk into a bar. The barmaid says "does everyone want a beer?"

The first mathematician says "I don't know."
The second mathematician says "I don't know."
The third mathematician says "No."

The barmaid, also a mathematician, pours two beers.

Three logicians walk into a bar. The barmaid says "does everyone want a beer?"

The first logician says "I don't know."
The second logician says "No"
The third one wants a beer. What does he say? "Yes", "No" OR "I don't know"

Or he says "no" because that's the answer to the question.
Or he could just order two beers.

Hahaha.. gr8 try .. but if he would say no, he wouldn't be sure of ending up with a beer.. The barmaid wouldn't be sure of whether he wanted a beer or not ;). If the barmaid wasn't into logic she wouldn't give him the beer(You are welcome to practically try it... and please do share the results :P)

First logician says "Don't know".
Second logician says "No".
Third logician says "No".
Barmaid says "So is that one or two beers?"

Practically, the original situation of 2 don't knows and a yes will only get you one beer.

yeah!! unless the barmaid is deep into logic :)

He would say "No, but I would like one."

Mike, thanks for the prominent link up top. "Coffee Logic" has now become the most clicked comic on the blog, beating out "Highly Irregular", which was an unofficial tie-in to a Irregular Webcomic storyline. Both of our comics are being linked in a bunch of places, and traffic at my site is up about 700% over normal.

Great. Now I have to keep it up! ;-)

No problem, I guess people really really love logic!

I get that each defaults to the last who has to make a choice that stands for all. So what is funny?
[What would really make this a funny joke is if, in a fifth, sixth, and seventh frame, the Waitress understood the order, made the order, and served the order correctly. This scenario would defy the basic laws of the Cosmos and leave everyone in stitches.]

Is it Logic or applied common sense

because they would simply say no ;p

oh, the hell with it. they're in a bar; they're drunk; they don't really understand the question, the ramifications, or the deeper meaning. they're just voicing their individual preferences. this is the "Gordian Knot" solution.

They're not drunk yet when ordering the beer :P

A similar (x, why?) comic.

three engineers walk into a bar and are asked the same question.
this time they may all be sure that they are all drinking / already drunk

This comic was printed in a German Math magazine :)

How can they know that the bartender also wants beer?

If you can answer the question of the following variation of the joke, you really understand it.
--------------
Three logicians walk into a bar. The bartender asks them: "Does everyone want beer ?"

"I don't know," said the first logician.

"I don't know," said the second logician.

"No," said the third logician.

If you are the bartender, what will you do ? In other words, do you know who wants beer and who does not ?

i think the point of it is the bartender asks a wrong question, which is not logical. and the 3rd person gives a wrong answer, which is not logical, either.
the question "does everyone want beer" should be "does anyone wants beer". it makes all three answers logical.

For the question "does anyone wants beer" the first logician would answer yes! as for it he alone would suffice to prove this premise.
This is like having (A and B and C) vs (A or B or C) as you suggest.
For (A and B and C) the value is undecided @A unless is false, @B the same only @C you know for sure what is the answer. In your case
the joke would still hold if she asked "is it not true that at least one of you don't want to have a beer?"

what if the third one said no?

The answer to the question is Yes. Why? because they wanted to challenge the bartender logic.

A: "i don't know"
B: "i don't know"
C: "Yes"
Bartender should think that YES is true because 1st individual didn't know what the next person wanted, and since they both said "I don't know", it comes to the last person who said "Yes". Its a multiple choice questions and the right answer to the question is D: all true
A: "I don't know" B: "I don't" know C: "Yes" D: All true

Given that the question is for everyone "Do you all want", then YES is true if and only if all three do want.
First one responds "I don't know", meaning "I do, but not sure is the remaining two do".
Second one responds, "I don't know", meaning "I do, but not sure is the remaining one does".
Third and last one responds Yes, knowing that the previous two do want, and so does he/she.
This is a logic of A ^ B ^ C -> True. Where all A and B and C must be true.

Why do the 2 logicians (in the middle) dress so plain, and the last dresses so fly? And he's the one who called beers for everyone. There's a bit of psychology to this cartoon too? If he were to be the second or first guy to answer, his answer could be "Sure! Beer for everyone."

at first glance does not make sense, but when you read the second time it is clear that the first and second guy can't say in the name of all, while last one, can !

As someone with a PhD in mathematical logic myself, I'd say that there is a problem with the question, as "Does everyone want beer?" doesn't restrict its domain to the three logicians. So the third logician surely still has to say that he doesn't know the answer - there are still people who haven't answered in the world somewhere. (And I'm making the perhaps unwarranted assumption that "everyone" is synonymous with "every person" here, still.)

It is illogical to think that if someone says "I dont know", it means that they want beer. A logician could have said "I dont know" purely for the sake of logic; He really doesn't know what everyone wants.

But the logician does know what he himself (or she herself) wants, if it is "No", then they can answer No truthfully to the question "Does everyone ...?"

Over a year later, and this page is still the biggest feeder into my comic. Which is amusing, so it makes me happy, but ironic, so also a little sad.

Good cartoon. The question gets the logicians to answer for everyone wanting beer. The first and second must answer "I don't know," leaving open the possibility of all logicians wanting beer. The last logician answers "yes," in this world. He could have answered "no" for another world. It's humorous because it does seem to represent a world of real life quite well.

beer= ab+c
the first character says i dont know, the second character will agree with the first character however the first and second character will agree with what the third character wants.

This is C. Burke of (x, why?). Thank you all for clicking the link and visiting my site, too. Another 800 hits just *today* and 1700 this week! Feel free to look around this site. For that matter, read the rest of Spiked Math -- it's more than just this one comic!

This is wrong! We can't assume that when the logicians say "I don't know" they mean yes they personally would like a beer but don't know about the others, that would not be logical. Why is there an assumption that saying " I don't know" automatically means "yes" rather than "no"?

Because if they didn't want a beer, then they could honestly say No, not everyone wants beer.

We could turn this into a logical puzzle: Three logicians walk into a bar and the bartender says to them "Do all of want a beer?" The first logician says "I don't know." The second logician says "I don't know." The third logician says "We'll have two beers." Who gets the beers?

(Corrected) We could turn this into a logical puzzle: Three logicians walk into a bar and the bartender says to them "Do all of YOU want a beer?" The first logician says "I don't know." The second logician says "I don't know." The third logician says "We'll have two beers." Who gets the beers?

I still don't get this. Saying "I don't know" might be necessary but it still doesn't convey the same semantic meaning as "yes". What the first two logicians seem to be conveying is indeterminacy at best. Under the rules of three value logic, two indeterminate responses and one true response combined in a conjunction would be false.

Not sure, the question is does everyone wants a beer? the first logician answer i dont know (the meaning of this is that this person doesnt know if the others want a beer, same with the se second person , the last person assume that the others want a beer and he answer yes but this is not true we dont know if the first or seconde logician want a beer , for me it doesnt have sense

To me this joke makes no sense. The statement "I don't Know" cannot infer whether Logicians 1 or 2 want a beer or not, it is merely a statement of fact that they do not know if everyone wants a beer. Hence Logician 3 cannot make the deduction that they all do.

Just to clarify further, the barman assumes all want beer, but this is not necessarily the case. One or more may want spirits, plain water or whatever. Similarly, the logicians themselves do not know each others preference, so the joke quickly unravels in complexity.

It is so clear that 1 and 2 WANT beer. They MUST. If they do NOT want beer, they are LYING when they say "I don't know" because they KNOW that NOT EVERYONE wants beer. Since they cannot lie, their "I don't know" REQUIRES that they themselves WANT beer. This is the basis of the logical assumption made by #3. Her "yes" is based on the FACT that she KNOWS that 1 and 2 MUST undeniably want beer or else they are lying about not knowing the true answer to the barmaid's question.

Heard this one before, and found it funny, but all good jokes, if you have to explain why it's funny, no one laughs. Anyway, here goes.

First make sure you read Bill's reply to comment from Hal (April 15, 2015).

Now, it's a given that they are logicians, and this is important. The #3 must not only be good at logic; to deduce that #1 and #2 want a beer, she must know that both of them reasoned correctly and completely. (BTW, #2 had to do the same for #1, so it goes double for #3, who has to trust that #2 knows #1 to be correct and complete just like #3 does.)

So, they must know each other so well to trust the other's reasoning to be correct and complete, and to trust that the others also trust the same (#3->#2->#1). And they do.

They know all these subtleties about each other, but they don't know--walking into a bar--if the others want a beer! :-)

No one might laugh, but some might grin, still! :-)

I love this. The 3rd Logician assumes the responsibility to speak for the 1st and 2nd logician as they responded with neutral answer - stating "i dont know"
therefore the 3rd spoke for the others. Also - the 3rd is dressed differently to 1 & 2 - But has a multi coloured top just like the Girl asking the question. So therefore - this can reveal that the 3rd has been to this bar before hahaha. And that the 3rd knows abit about the place so answers with confidence. there you go

Welcome to Spiked Math!

Hello my fellow math geeks. My name is Mike and I am the creator of Spiked Math Comics, a math comic dedicated to humor, educate and entertain the geek in you. Beware though, there might be some math involved :D

New to Spiked Math?
View the top comics.

New Feature: Browse the archives in quick view! Choose from a black, white or grey background.

Now you can discuss the comics in the

Apps

by Pablo and Leonardo

Android app
by Bryan

Available on:
Swoopy app

Other Sites: