Jump to content

Welcome to BrainDen.com - Brain Teasers Forum

Welcome to BrainDen.com - Brain Teasers Forum. Like most online communities you must register to post in our community, but don't worry this is a simple free process. To be a part of BrainDen Forums you may create a new account or sign in if you already have an account.
As a member you could start new topics, reply to others, subscribe to topics/forums to get automatic updates, get your own profile and make new friends.

Of course, you can also enjoy our collection of amazing optical illusions and cool math games.

If you like our site, you may support us by simply clicking Google "+1" or Facebook "Like" buttons at the top.
If you have a website, we would appreciate a little link to BrainDen.

Thanks and enjoy the Den :-)
Guest Message by DevFuse

* * * * * 1 votes

Double Liar Paradox (Jourdain's paradox)

  • Please log in to reply
63 replies to this topic

#1 rookie1ja


    Senior Member

  • Site Admin
  • PipPipPipPip
  • 1344 posts
  • Gender:Male
  • Location:Slovakia

Posted 09 June 2007 - 12:44 PM

Double Liar Paradox (Jourdain's paradox) - Back to the Paradoxes

This version of the famous paradox was presented by an English mathematician P. E. B. Jourdain in 1913.
The following inscriptions are on a paper:

Back side
Inscription on the other side is true

Face side
Inscription on the other side is not true
  • 0

rookie1ja (site admin)
Optical Illusions
Support BrainDen

"To start: Press any key... Where's the 'any' key?" - Homer Simpson

#2 unreality


    Senior Member

  • Members
  • PipPipPipPip
  • 6375 posts

Posted 03 July 2007 - 02:24 AM

a much simpler liars paradox:

"This statement is a lie"

if its telling the truth then its lying

if its lying then its telling the truth

  • 0

#3 bonanova



  • Moderator
  • PipPipPipPip
  • 6161 posts
  • Gender:Male
  • Location:New York

Posted 20 July 2007 - 06:22 AM

What underlies paradoxes of this type is the syntactical rule
that a declarative sentence is by its nature an assertion of
some particular truth. To use a presumed assertion of
truth to deny that same truth is paradoxical: One cannot
convey usable knowledge by asserting a denial. Nor can one
meaningfully deny a truth: the coin has two paradoxical

[1] "I am asserting a falsehood." or "I am lying."
[2] "I am not asserting something that is true." or "I am not telling the truth."

Putting it another way, it's physically possible to speak the
words, "I am lying." But when one undertakes a linear
analysis of what has happened when the words are spoken,
one is drawn into the syntactical analogy of a Moebius Strip:
a piece of paper having a physical connection of its two sides.

The circular reasoning forced on the mind by a linear
analysis of such statements creates a pleasantly frustrating
tease, and the desire for consistency and meaning leaves
one in a disturbingly uncomfortable state.

Long live paradoxes...
  • 0

Vidi vici veni.

#4 Babers-san



  • Members
  • Pip
  • 12 posts

Posted 20 July 2007 - 06:48 AM

I don't quite understand the fascination with 'paradoxes' of this sort, which basically come down to which of the two statements are true, if any.

I am blue.
I am red.

Am I blue or red? Maybe I'm green. Doesn't matter, both cannot be true.

The truth is on the other side.
The other side holds no truths.

Or is that just it? We enjoy 'trapping' the mind in a room with mirrors on both the wall we are facing and the wall directly behind, and looking at the infinite reflections that result?

I just don't get it. Can someone tell me what I am missing?

I am reminded of the "bullet that pierces all vs. armour that cannot be pierced" contradiction. Similar situation, both just cannot exist. One is right, the other is wrong, or maybe both are wrong, but the contradictory elements cannot both be right.
  • 0

#5 bonanova



  • Moderator
  • PipPipPipPip
  • 6161 posts
  • Gender:Male
  • Location:New York

Posted 20 July 2007 - 07:49 AM

I don't quite understand the fascination with 'paradoxes' of this sort, which basically come down to which of the two statements are true, if any.


Can someone tell me what I am missing?

It's the fact that one statement can be a contradiction.

[1] "I am lying."

Spreading that over two statements does not change the
nature of the paradox:

[2] "I am telling the truth."
[3] "The previous statement is a lie."

Here, one can simply eliminate statement [2],
which carries no information, and change [3] into

[4] "This statement is a lie."

which is equivalent to statement [1].

To my mind the paradox arises from an explicit assertion of something's falseness
using a vehicle [declarative sentence] which implicitly asserts its truth.
  • 0

Vidi vici veni.

#6 wsguede



  • Members
  • Pip
  • 1 posts

Posted 28 July 2007 - 02:53 PM

it is just like in math.
rule 1) 0 * anything is.... 0
rule 2) infinity * anything is... infinity

whats 0*infinity?
what is that absence of everything * the fulfilliment of everything?

its impossible to end the problem, unless u know calc.

i do believe that it is an infinit loop. but then again, it could be based on how u read it. and your thought process
  • 0

#7 Linewalker



  • Members
  • Pip
  • 3 posts

Posted 31 July 2007 - 07:01 PM

The lying example doesn't work. Lying and not telling the truth are entirely different. When you lie, you are telling someone something that you believe is incorrect. When you don't tell the truth, you are still able to say what you believe, be incorrect, and not be lying about it.

The tricky part with this paradox is that one statement means nothing without the other. In any event where the statement can stand alone it's not a paradox. Ex: "This statement is false." The statement that is being called false is false, while the entire sentence is true. What is false does not include the word false itself.

The only circular part about this problem is trying to figure it out. The problem itself isn't circular, they both exist at the same time, in the same space.

Even knowing that, I'm having a hard time getting out of the circle. Can anyone else get out of it?
  • 0

#8 retskcah .eht

retskcah .eht


  • Members
  • Pip
  • 8 posts

Posted 08 August 2007 - 11:02 AM

non of inscriptios are true.
becouse "the truth is absolute definition of an event acordingly to our reality"
retskcah .eht 8.8 2007
*this is not an event but a contradictional statement.*
  • 0

#9 bptdude



  • Members
  • Pip
  • 3 posts

Posted 22 August 2007 - 02:08 AM

absolute truth?

depending on culture and education, some people will fight to the death that there is no such thing as any absolute truth about anything, even for things that seem obvious.

"well, that's that's your opinion" or "well, not really, exactly, because of this obscure thing"

for a paradox "this is a lie" .. you have to dig into the definitions of a lie.
and something not being a lie does not make it a truth.
  • 0

#10 impact504



  • Members
  • Pip
  • 6 posts

Posted 28 August 2007 - 09:16 PM

This reminds me of the movie Labrynth.

"does that sound right to you?"

"I dont know, Ive never understood it!!"
  • 0

0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users