Can you solve the famously difficult green-eyed logic puzzle? - Alex Gendler

  • Published on: 16 June 2015
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    One hundred green-eyed logicians have been imprisoned on an island by a mad dictator. Their only hope for freedom lies in the answer to one famously difficult logic puzzle. Can you solve it? Alex Gendler walks us through this green-eyed riddle.

    Lesson by Alex Gendler, animation by Artrake Studio.
  • Runtime : 4:42
  • TEd TED-Ed TEDx TEDEducation Alex Gendler Philosophy Logic Riddle Dictator Dictatorship Prison Puzzle Common Knowledge David Lewis Artrake Studio


  • smallWORLD
    smallWORLD   2 hours ago

    Nice! I lived with a variation of this riddle called red-eyed monks.Basically it goes like this:There are some monks in a monastery with no water, metal or mirrors. There are two rules: No interfering other monks meditationNo RED EYESIf a monk discovers that they have red eyes then they must immediately leave the night after they find out. Then a visitor comes and says "at least one of you has red eyes!"- What happens is, if there is one monk with red eyes, then he will notice that everyone else has white eyes and he will leave. - If there are two monks with red eyes, they won't leave at first because they can see another monk with red eyes. However, after that they will both realise that the other one didn't leave, therefore they must both leave. This situation happens with three monks (realising on the third night that the two other monks didn't leave) four monks, five monks, any amount of monks.

  • siquod
    siquod   10 hours ago

    So prisoner 1 didn't know if prisoner 2 knew if prisoner 3 knew if … if prisoner 100 knew there was at least one green eyed person. Weird.

  • Jdj Dfg
    Jdj Dfg   2 days ago

    I’d have said “The people next to you have green eyes.” It was told to everyone and since they know that the two people next to everyone have green eyes they could all leave on the first night.

    SUJAN K C   2 days ago

    I would have said to the logicians to roll their eyes in front of a green eyed person..............Case is solved.....All are freed in a single night

  • PhoenixGamer10 | Gaming

    Well, if it was that bad, I’d off myself, and the easiest way is to ask the guards if i could leave.

  • Lily sung
    Lily sung   3 days ago

    Looking at the comment section, I’m starting to wonder if I’m focusing too much on the mad dictator part. I thought the point was to come up with the most subtle clue possible that the dictator won’t notice right off the bat.

  • user
    user   3 days ago

    I disagree. The maximum not-new information is: "at least 98 of you have green eyes". If you see 99 others with green eyes you aren't sure if they see you with green eyes too, so your conclusion is "everyone sees AT LEAST 98 others with green eyes".

    ANDROLOMA   4 days ago

    Sugarloaf's green-eyed lady solved the green-eyed puzzle. But she was a one-hit wonder, and faded into obscurity.

  • Whatmouse
    Whatmouse   4 days ago

    There is one impostor among you

  • Bogers
    Bogers   4 days ago

    Could you not have said, 'the person next to you has green eyes' you're not directly telling them new information about themselves, but they can deduce that everyone must have green eyes

  • Glacial
    Glacial   5 days ago

    This was a math probelm in my class lol

  • Madan Matcha
    Madan Matcha   5 days ago

    I know! If you are watching on chromebook turn high contrast and dictator has green eyes so ask him to leave or toss him into the volcano

  • Alvin Wong
    Alvin Wong   1 weeks ago

    Take a picture and show it to the peopleb o o m

  • Bamnt
    Bamnt   1 weeks ago

    but telling them one of them has green eyes is a nee information

  • Aan Nasution
    Aan Nasution   1 weeks ago

    I would just put water on the ground then see.

  • Madan Matcha
    Madan Matcha   1 weeks ago

    Make fake robot people and run out and look at the water

  • Madan Matcha
    Madan Matcha   1 weeks ago

    They should watch this video so they can see that they have green eyes

  • Amy Prosser
    Amy Prosser   1 weeks ago

    Just look in the reflection of someone else's eye at your own eye

  • MultiBagram
    MultiBagram   1 weeks ago

    I am having a lot of trouble with this. The premises are weird. And I can't follow the reasoning, when it goes to three prisoners.

  • astridh
    astridh   1 weeks ago

    wouldn’t “at least 99 of you have green eyes” work better? nobody would leave the first night in fear of being the one person without green eyes. however, after nobody leaves they would all realise that everyone else must also see 99 people with green eyes, including you. then everyone leaves on the second night. we know that all of the prisoners see 99 others with green eyes so it’s not really new information to them

  • noname76141
    noname76141   1 weeks ago

    WhY dO tHeY iMpRiSoN pEoPLe WiTh GrEeN eYeS???!!1

  • Ray Cooper
    Ray Cooper   1 weeks ago

    Ah if you tell them one of them has green eyes they'll realise they have the same eye coulor

  • Mix_Of_Everything
    Mix_Of_Everything   1 weeks ago

  • Derek Tomas
    Derek Tomas   1 weeks ago

    But they all knew at least one had green eyes from seeing others, couldn't they have just done this before

  • Oluwatobi Aikomo
    Oluwatobi Aikomo   1 weeks ago

    "Every prisoner you can see around you has green eyes" is not new information, and would have worked perfectly. All of them would have left the following night and not need to wait for 100 days.

  • Liana Lyods
    Liana Lyods   1 weeks ago

    I don't understand how this works. If I was one of the prisoners given this information I would have stayed at the island because I would just assume the other prisoners must be thinking of something else other than escape or green eyes.