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Barber Paradox - Printable Version

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Barber Paradox - Tank123 - 04-11-2011 12:17 AM

Here is an interesting mathematical paradox for those interested in Mathematics or in general:

The paradox involves a male barber in a town, who everyday shaves every man who does not shave himself, does the barber shave himself?


The paradox seems to demand that the barber shave himself if and only if he does not shave himself!  This paradox was proposed by Mathematician and Philosopher Bertrand Russel.  It still has not been solved today, but nevertheless it forced a modification to set theory in Mathematics.


RE: Barber Paradox - skyblue1 - 04-11-2011 12:47 AM

not much of a paradox, especially if the barber wore a beard.


RE: Barber Paradox - Vampslord - 04-11-2011 12:50 AM

And it does not implies that he shave only the man who dont shave. Only that he shave all the man who dont.


RE: Barber Paradox - Tank123 - 04-11-2011 01:10 AM

skyblue1  Wrote:
not much of a paradox, especially if the barber wore a beard.


In a mathematical paradox, there is no double meaning behind the statements.  It is a paradox because it implies that the barber shave himself if and only if he does not shave himself.


RE: Barber Paradox - Tank123 - 04-11-2011 01:11 AM

Vampslord Wrote:
And it does not implies that he shave only the man who dont shave. Only that he shave all the man who dont.


There is no double meaning behind this paradox.


RE: Barber Paradox - d_olson27 - 04-11-2011 01:38 AM

Tank123 Wrote:

Vampslord Wrote:
And it does not implies that he shave only the man who dont shave. Only that he shave all the man who dont.


There is no double meaning behind this paradox.


Where does it say that?


RE: Barber Paradox - skyblue1 - 04-11-2011 02:11 AM

Tank123 Wrote:

skyblue1  Wrote:
not much of a paradox, especially if the barber wore a beard.


In a mathematical paradox, there is no double meaning behind the statements.  It is a paradox because it implies that the barber shave himself if and only if he does not shave himself.


there is no math involved


RE: Barber Paradox - 142857 - 04-11-2011 02:57 AM

I can see the value in this as a thought experiment, and even though I don't have a lot of knowledge of higher mathematics I can see how it would affect set theory.

What it shows is that a simple "either/or" statement can actually imply 3 categories, not just 2.

You have to move beyond the idea that there are two types of men in the town, as implied by the original statement - those who shave themselves and those who are shaved by the barber. The barber himself is obviously a 3rd category not covered by the statement.

I don't think that there is much point trying to "solve" it, though, as there is about as much chance of solving this one as there is of solving definitively "which came first, the chicken or the egg?".


RE: Barber Paradox - 142857 - 04-11-2011 02:58 AM

skyblue1  Wrote:
there is no math involved


Not directly. But it does have implications for set theory, which is part of mathematics.


RE: Barber Paradox - d_olson27 - 04-11-2011 03:21 AM

142857 Wrote:
I don't think that there is much point trying to "solve" it, though, as there is about as much chance of solving this one as there is of solving definitively "which came first, the chicken or the egg?".


If you believe in evolution, obviously the egg came first.


RE: Barber Paradox - Tank123 - 04-11-2011 03:27 AM

d_olson27 Wrote:

Tank123 Wrote:

Vampslord Wrote:
And it does not implies that he shave only the man who dont shave. Only that he shave all the man who dont.


There is no double meaning behind this paradox.


Where does it say that?


It doesn't have to say that.  Within a mathematical context such as this, what is said is all that is allowed to be worked with.  In other words, there can be no one else that shaves the barber, for example.


RE: Barber Paradox - d_olson27 - 04-11-2011 03:35 AM

Tank123 Wrote:

d_olson27 Wrote:

Tank123 Wrote:

Vampslord Wrote:
And it does not implies that he shave only the man who dont shave. Only that he shave all the man who dont.


There is no double meaning behind this paradox.


Where does it say that?


It doesn't have to say that.  Within a mathematical context such as this, what is said is all that is allowed to be worked with.  In other words, there can be no one else that shaves the barber, for example.


Source?


RE: Barber Paradox - 142857 - 04-11-2011 03:45 AM

d_olson27 Wrote:

142857 Wrote:
I don't think that there is much point trying to "solve" it, though, as there is about as much chance of solving this one as there is of solving definitively "which came first, the chicken or the egg?".


If you believe in evolution, obviously the egg came first.


So something that was not a chicken laid an egg that had a chicken inside it - and what hatched out was the first true chicken?

Actually you are right - in evolutionary terms, the egg has to come first.


RE: Barber Paradox - Tank123 - 04-11-2011 04:09 AM

d_olson27 Wrote:

Tank123 Wrote:

d_olson27 Wrote:

Tank123 Wrote:

Vampslord Wrote:
And it does not implies that he shave only the man who dont shave. Only that he shave all the man who dont.


There is no double meaning behind this paradox.


Where does it say that?


It doesn't have to say that.  Within a mathematical context such as this, what is said is all that is allowed to be worked with.  In other words, there can be no one else that shaves the barber, for example.


Source?


Mathematics is my source.  Mathematical language is much more specific meaning than everyday, ordinary language.  When something is stated or implied, there are no double meanings at all involved.


RE: Barber Paradox - d_olson27 - 04-11-2011 04:16 AM

Tank123 Wrote:

d_olson27 Wrote:

Tank123 Wrote:

d_olson27 Wrote:

Tank123 Wrote:

Vampslord Wrote:
And it does not implies that he shave only the man who dont shave. Only that he shave all the man who dont.


There is no double meaning behind this paradox.


Where does it say that?


It doesn't have to say that.  Within a mathematical context such as this, what is said is all that is allowed to be worked with.  In other words, there can be no one else that shaves the barber, for example.


Source?


Mathematics is my source.  Mathematical language is much more specific meaning than everyday, ordinary language.  When something is stated or implied, there are no double meanings at all involved.


But your statement is not mathematical in nature. As soon as your language becomes removed from mathematics in any way, there are multiple ways it can be interpreted. In this case, the question does not exclude the possibility of the barber shaving himself and being shaved by the barber.


RE: Barber Paradox - WASPIE - 04-11-2011 04:21 AM

Tank123 Wrote:

skyblue1  Wrote:
not much of a paradox, especially if the barber wore a beard.


In a mathematical paradox, there is no double meaning behind the statements.  It is a paradox because it implies that the barber shave himself if and only if he does not shave himself.

Nicely said and this is why it is autistic in nature.


RE: Barber Paradox - Tank123 - 04-11-2011 04:25 AM

d_olson27 Wrote:

Tank123 Wrote:

d_olson27 Wrote:

Tank123 Wrote:

d_olson27 Wrote:

Tank123 Wrote:

Vampslord Wrote:
And it does not implies that he shave only the man who dont shave. Only that he shave all the man who dont.


There is no double meaning behind this paradox.


Where does it say that?


It doesn't have to say that.  Within a mathematical context such as this, what is said is all that is allowed to be worked with.  In other words, there can be no one else that shaves the barber, for example.


Source?


Mathematics is my source.  Mathematical language is much more specific meaning than everyday, ordinary language.  When something is stated or implied, there are no double meanings at all involved.


But your statement is not mathematical in nature. As soon as your language becomes removed from mathematics in any way, there are multiple ways it can be interpreted. In this case, the question does not exclude the possibility of the barber shaving himself and being shaved by the barber.


But my statement is mathematical in nature.  That is because Mathematics is in some sense essentially logic.  Just because it does not contain numbers, does not mean it is not mathematical.  Using mathematical language, this paradox involves the set of all sets that aren't members of themselves.  Many sets R are not members of themselves-for example, the set of cubes is not a cube.  Examples of sets T that do contain themselves as members are the set of all sets, or the set of all things except cubes.  Every set would seem to be either of Type R or of Type T, and no set can be both.  However, when Russel was forming this paradox, he wondered about the set S of all sets that aren't members of themselves.  Somehow, S is neither a member of itself nor not a member of itself.

I know this seems mind boggling, but in the words of mathematician Ronald Graham, "Our brains have evolved to get us out of the rain, find where the berries are, and keep us from getting killed.  Our brains did not evolve to help us grasp really large numbers or to look at things in a hundred thousand dimensions."


RE: Barber Paradox - d_olson27 - 04-11-2011 04:37 AM

Tank123 Wrote:
But my statement is mathematical in nature.  That is because Mathematics is in some sense essentially logic.  Just because it does not contain numbers, does not mean it is not mathematical.  Using mathematical language, this paradox involves the set of all sets that aren't members of themselves.  Many sets R are not members of themselves-for example, the set of cubes is not a cube.  Examples of sets T that do contain themselves as members are the set of all sets, or the set of all things except cubes.  Every set would seem to be either of Type R or of Type T, and no set can be both.  However, when Russel was forming this paradox, he wondered about the set S of all sets that aren't members of themselves.  Somehow, S is neither a member of itself nor not a member of itself.

I know this seems mind boggling, but in the words of mathematician Ronald Graham, "Our brains have evolved to get us out of the rain, find where the berries are, and keep us from getting killed.  Our brains did not evolve to help us grasp really large numbers or to look at things in a hundred thousand dimensions."


So, in other words, this barber paradox has nothing to do with reality in any way.

Also, I hate to break it to you, but ambiguity and double meanings do exist in mathematics. Example: the square root of 4 is both 2 and -2.


RE: Barber Paradox - 142857 - 04-11-2011 04:39 AM

I can see the value in this paradox, and I can see how it has the implications for set theory that you stated above.

But all it boils down to is that you cannot always encapsulate every possibility with a simple either/or statement. In this case the statement implies that there are two types of men in the town, when in fact there must be at least 3.

It doesn't need to be mind boggling - it is pretty simple really.

Think about it this way: this is only mind boggling if you go in with the expectation that a simple either/or statement can always cover every possibility - and your mind then refuses to let go of that expectation.


RE: Barber Paradox - 142857 - 04-11-2011 04:43 AM

d_olson27 Wrote:
Also, I hate to break it to you, but ambiguity and double meanings do exist in mathematics. Example: the square root of 4 is both 2 and -2.


The square root of 4 is 2. Even though, by logic, it can be both 2 and -2, the convention is that it is 2.

If X^2 = 4, then X = 2 or -2.

This is one of those technicalities that some high school teachers try to catch their students out on.


RE: Barber Paradox - Tank123 - 04-11-2011 04:53 AM

142857 Wrote:
I can see the value in this paradox, and I can see how it has the implications for set theory that you stated above.

But all it boils down to is that you cannot always encapsulate every possibility with a simple either/or statement. In this case the statement implies that there are two types of men in the town, when in fact there must be at least 3.

It doesn't need to be mind boggling - it is pretty simple really.

Think about it this way: this is only mind boggling if you go in with the expectation that a simple either/or statement can always cover every possibility - and your mind then refuses to let go of that expectation.


Oh, no.  You are completely right.  What I meant when I said 'mind-boggling' was the part when I talked about how for example, not all sets are sets of themselves.  This kind of language can be hard for people to understand at first, including myself.


RE: Barber Paradox - Tank123 - 04-11-2011 04:56 AM

d_olson27 Wrote:

Tank123 Wrote:
But my statement is mathematical in nature.  That is because Mathematics is in some sense essentially logic.  Just because it does not contain numbers, does not mean it is not mathematical.  Using mathematical language, this paradox involves the set of all sets that aren't members of themselves.  Many sets R are not members of themselves-for example, the set of cubes is not a cube.  Examples of sets T that do contain themselves as members are the set of all sets, or the set of all things except cubes.  Every set would seem to be either of Type R or of Type T, and no set can be both.  However, when Russel was forming this paradox, he wondered about the set S of all sets that aren't members of themselves.  Somehow, S is neither a member of itself nor not a member of itself.

I mean double meaning does not exist in mathematics in the sense of like figurative language and such.  For example, when I say that:

If A=B, then A+C=B+C

There is no double meaning behind this or any other mathematical expression.  It is what one sees and nothing else.

I know this seems mind boggling, but in the words of mathematician Ronald Graham, "Our brains have evolved to get us out of the rain, find where the berries are, and keep us from getting killed.  Our brains did not evolve to help us grasp really large numbers or to look at things in a hundred thousand dimensions."


So, in other words, this barber paradox has nothing to do with reality in any way.

Also, I hate to break it to you, but ambiguity and double meanings do exist in mathematics. Example: the square root of 4 is both 2 and -2.




RE: Barber Paradox - Tank123 - 04-11-2011 04:58 AM

d_olson27 Wrote:

Tank123 Wrote:
But my statement is mathematical in nature.  That is because Mathematics is in some sense essentially logic.  Just because it does not contain numbers, does not mean it is not mathematical.  Using mathematical language, this paradox involves the set of all sets that aren't members of themselves.  Many sets R are not members of themselves-for example, the set of cubes is not a cube.  Examples of sets T that do contain themselves as members are the set of all sets, or the set of all things except cubes.  Every set would seem to be either of Type R or of Type T, and no set can be both.  However, when Russel was forming this paradox, he wondered about the set S of all sets that aren't members of themselves.  Somehow, S is neither a member of itself nor not a member of itself.

I know this seems mind boggling, but in the words of mathematician Ronald Graham, "Our brains have evolved to get us out of the rain, find where the berries are, and keep us from getting killed.  Our brains did not evolve to help us grasp really large numbers or to look at things in a hundred thousand dimensions."


So, in other words, this barber paradox has nothing to do with reality in any way.

Also, I hate to break it to you, but ambiguity and double meanings do exist in mathematics. Example: the square root of 4 is both 2 and -2.


It actually has everything to do with reality.  Mathematics is reality.


RE: Barber Paradox - Tank123 - 04-11-2011 05:00 AM

142857 Wrote:
I can see the value in this paradox, and I can see how it has the implications for set theory that you stated above.

But all it boils down to is that you cannot always encapsulate every possibility with a simple either/or statement. In this case the statement implies that there are two types of men in the town, when in fact there must be at least 3.

It doesn't need to be mind boggling - it is pretty simple really.

Think about it this way: this is only mind boggling if you go in with the expectation that a simple either/or statement can always cover every possibility - and your mind then refuses to let go of that expectation.


But in this case it is an either/or setting.  It is true that you cannot always encapsulate reality and logic with either/or statements, but for this one that principle holds true.


RE: Barber Paradox - 142857 - 04-11-2011 05:01 AM

Tank123 Wrote:
Mathematics is reality.


Or is mathematics just a really useful way of representing reality?


RE: Barber Paradox - Tank123 - 04-11-2011 05:04 AM

142857 Wrote:

Tank123 Wrote:
Mathematics is reality.


Or is mathematics just a really useful way of representing reality?


Our mathematical notation is a really useful way of representing reality, which is mathematical truths.  According to some, Mathematics could run reality just like software runs a computer.  According to Mathematical Universe Hypothesis (MUH) Our physical reality is not just described by mathematics, it is Mathematics.  We don't invent Mathematical truths, we discover them and we only invent the notation for describing them.


RE: Barber Paradox - d_olson27 - 04-11-2011 05:06 AM

142857 Wrote:

Tank123 Wrote:
Mathematics is reality.


Or is mathematics just a really useful way of representing reality?


I'm going with that one.


RE: Barber Paradox - Tank123 - 04-11-2011 05:08 AM

d_olson27 Wrote:

142857 Wrote:

Tank123 Wrote:
Mathematics is reality.


Or is mathematics just a really useful way of representing reality?


I'm going with that one.


haha, i guess i will never be able to convert you to mathematics, huh?Smile


RE: Barber Paradox - d_olson27 - 04-11-2011 05:15 AM

Tank123 Wrote:

d_olson27 Wrote:

142857 Wrote:

Tank123 Wrote:
Mathematics is reality.


Or is mathematics just a really useful way of representing reality?


I'm going with that one.


haha, i guess i will never be able to convert you to mathematics, huh?Smile


I never said I wasn't a fan of mathematics. Just that it doesn't work for everything. Either that or you're using the wrong set of rules for the specific example that was given. As 142857 pointed out, you're using 'either/or' rules for a situation that is not 'either/or' in nature.


RE: Barber Paradox - Tank123 - 04-11-2011 05:23 AM

d_olson27 Wrote:

Tank123 Wrote:

d_olson27 Wrote:

142857 Wrote:

Tank123 Wrote:
Mathematics is reality.


Or is mathematics just a really useful way of representing reality?


I'm going with that one.


haha, i guess i will never be able to convert you to mathematics, huh?Smile


I never said I wasn't a fan of mathematics. Just that it doesn't work for everything. Either that or you're using the wrong set of rules for the specific example that was given. As 142857 pointed out, you're using 'either/or' rules for a situation that is not 'either/or' in nature.


I know, i was kiddingSmile  

I do think that mathematics works for everything though.  I think that it not only works for everything, but it is everything.

The paradox is either/or though in nature.

Every day the male barber shaves every man who does not shave himself, and no one else.  Does the barber shave himself?

That is an either/or expression.


RE: Barber Paradox - d_olson27 - 04-11-2011 05:37 AM

Tank123 Wrote:

d_olson27 Wrote:

Tank123 Wrote:

d_olson27 Wrote:

142857 Wrote:

Tank123 Wrote:
Mathematics is reality.


Or is mathematics just a really useful way of representing reality?


I'm going with that one.


haha, i guess i will never be able to convert you to mathematics, huh?Smile


I never said I wasn't a fan of mathematics. Just that it doesn't work for everything. Either that or you're using the wrong set of rules for the specific example that was given. As 142857 pointed out, you're using 'either/or' rules for a situation that is not 'either/or' in nature.


I know, i was kiddingSmile  

I do think that mathematics works for everything though.  I think that it not only works for everything, but it is everything.

The paradox is either/or though in nature.

Every day the male barber shaves every man who does not shave himself, and no one else.  Does the barber shave himself?

That is an either/or expression.


That part in bold is a key detail that you left out of the original version. Now it's a paradox.


RE: Barber Paradox - Tank123 - 04-11-2011 05:53 AM

d_olson27 Wrote:

Tank123 Wrote:

d_olson27 Wrote:

Tank123 Wrote:

d_olson27 Wrote:

142857 Wrote:

Tank123 Wrote:
Mathematics is reality.


Or is mathematics just a really useful way of representing reality?


I'm going with that one.


haha, i guess i will never be able to convert you to mathematics, huh?Smile


I never said I wasn't a fan of mathematics. Just that it doesn't work for everything. Either that or you're using the wrong set of rules for the specific example that was given. As 142857 pointed out, you're using 'either/or' rules for a situation that is not 'either/or' in nature.


I know, i was kiddingSmile  

I do think that mathematics works for everything though.  I think that it not only works for everything, but it is everything.

The paradox is either/or though in nature.

Every day the male barber shaves every man who does not shave himself, and no one else.  Does the barber shave himself?

That is an either/or expression.


That part in bold is a key detail that you left out of the original version. Now it's a paradox.


I did make that mistake and I apologize for it. I forgot about those words and somehow I skipped past them.


RE: Barber Paradox - 142857 - 04-11-2011 06:03 AM

d_olson27 Wrote:

Tank123 Wrote:

d_olson27 Wrote:

Tank123 Wrote:

d_olson27 Wrote:

142857 Wrote:

Tank123 Wrote:
Mathematics is reality.


Or is mathematics just a really useful way of representing reality?


I'm going with that one.


haha, i guess i will never be able to convert you to mathematics, huh?Smile


I never said I wasn't a fan of mathematics. Just that it doesn't work for everything. Either that or you're using the wrong set of rules for the specific example that was given. As 142857 pointed out, you're using 'either/or' rules for a situation that is not 'either/or' in nature.


I know, i was kiddingSmile  

I do think that mathematics works for everything though.  I think that it not only works for everything, but it is everything.

The paradox is either/or though in nature.

Every day the male barber shaves every man who does not shave himself, and no one else.  Does the barber shave himself?

That is an either/or expression.


That part in bold is a key detail that you left out of the original version. Now it's a paradox.


The funny thing is that I assumed the bold text when I read the opening post, even though it is not clearly implied. I read the statement expecting it to be a paradox, and it is not a paradox unless it is assumed that the barber shaves every man who does not shave himself and no one else. So I guess I filled in the gaps to make it a paradox.

I see the original statement as implying an either/or situation because it implies that every man in the town either shaves himself or is shaved by the barber. But the barber himself does not fit on either side of that either/or statement. The paradox lies in the expectation that an either/or statement can always cover every possibility. The clear implication for set theory is that it cannot.


RE: Barber Paradox - billyt - 04-11-2011 10:14 AM

He has low testosterone (he sings falsetto in the barbershop quartet - the other three of whom he shaves) and therefore has a face like a baby's bottom. Having no beard in any case he doesn't not shave..he merely doesn't have too. Fankie Valley had this issue, despite being Italian. Something to do with pollution and nukes in NJ.


RE: Barber Paradox - Vampslord - 04-11-2011 12:45 PM

He could just trim his beard.


RE: Barber Paradox - Alison - 04-11-2011 01:45 PM

The barber's a woman.  And Bertrand Russell really needs to get out and meet some nice girls and get himself laid more.
Alison


RE: Barber Paradox - Tank123 - 04-12-2011 12:08 AM

Vampslord Wrote:
He could just trim his beard.


he has to shave it completely.


RE: Barber Paradox - skyblue1 - 04-12-2011 12:37 AM

so the OP was incorrect in its text to begin with?


RE: Barber Paradox - d_olson27 - 04-12-2011 01:00 AM

skyblue1  Wrote:
so the OP was incorrect in its text to begin with?


Yep. I'm satisfied with it as a paradox now.


RE: Barber Paradox - ArianiaAmy - 04-12-2011 08:27 AM

Haha.  I almost said the barber lost his beard in chemotherapy.  That doesn't solve it though, I know because he's still a man and all men in this town must either shave themself or have the barber shave them.  There's a no beard or other hair loss policy it seems.

Wait!  The barber is still just a boy!  They don't have child labor laws there and his parents let him play with sharp objects.  It just says male, not male adult.

But doubtful....  Nice paradox  Smile