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  1. #61
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    Re: What is Logic? (Logic 101)

    Quote Originally Posted by curious boy View Post
    I have met this kind of problem the other year in our elementary science magazine. The version used tribes instead of a twin.

    But considering the key parts (given) in the problem, my question is:



    But you only know that one of them ALWAYS lie, then you may not know that it could be the liar who would say, "My liar brother would tell you to go this way (the right way)" since he always lie and could possibly lie with his identity.

    What about that?
    It makes no difference whether the brother you speak to is the liar or the truth-teller. One way or the other, the solution works and will work every time. The question is structured in such a way that no matter which brother you ask you will get pointed to the wrong path
    "I am against religion because it teaches us to be satisfied with not understanding the world" - Richard Dawkins

    "If you could rationalize with Religious people there would be no more Religious people" -Gregory House

  2. #62
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    Re: What is Logic? (Logic 101)

    But logic doesn't always have to go for situations, does it? Couldn't it be more applied to things such as a logical thinking process?
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  3. #63
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    Re: What is Logic? (Logic 101)

    Quote Originally Posted by Allocutus View Post
    It makes no difference whether the brother you speak to is the liar or the truth-teller. One way or the other, the solution works and will work every time. The question is structured in such a way that no matter which brother you ask you will get pointed to the wrong path
    I don't directly agree.

    If you ask them the question, "What path would your brother tell me to take to get to my destination?":

    If you have asked the Liar brother, he will always lie and could tell you, "My liar brother would tell you to go here (points the right road)"
    (lied with his identity)

    and in accordance to the solution, you will take the opposite path

    Is that possible?

  4. #64
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    Re: What is Logic? (Logic 101)

    Quote Originally Posted by curious boy View Post
    I don't directly agree.

    If you ask them the question, "What path would your brother tell me to take to get to my destination?":

    If you have asked the Liar brother, he will always lie and could tell you, "My liar brother would tell you to go here (points the right road)"
    (lied with his identity)

    and in accordance to the solution, you will take the opposite path

    Is that possible?
    Yes, that's possible. But because the liar brother has to lie, he'll lie about what his truth-telling brother would say about which way is the right way to go
    "I am against religion because it teaches us to be satisfied with not understanding the world" - Richard Dawkins

    "If you could rationalize with Religious people there would be no more Religious people" -Gregory House

  5. #65
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    Re: What is Logic? (Logic 101)

    Hm. I've heard this riddle many times, but I don't get it.

    Let's see.

    ---------------------------------------------

    If you ask the liar brother - which path would your brother tell me to go? - you would get:

    1) My LIAR brother would tell you to the the RIGHT path.
    2) My TRUTHFUL brother would tell you to take the RIGHT path.
    3) My LIAR brother would tell you to take the LEFT path.
    4) My TRUTHFUL brother would tell you to take the RIGHT path.

    Then you could ask the other brother the same question and he would reply with...:

    1) My LIAR brother would tell you to the the RIGHT path.
    2) My TRUTHFUL brother would tell you to take the RIGHT path.
    3) My LIAR brother would tell you to take the LEFT path.
    4) My TRUTHFUL brother would tell you to take the RIGHT path.

    ...the same thing. So, if they looked the same, and no way of telling the difference, then you would have no idea where to go.

    Or am I not getting something?
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  6. #66
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    Re: What is Logic? (Logic 101)

    My point is, it is a problem. And the "given" should be considered a law, along with logic (basic) to come up with the positive answer and again, according to the "given". So, the lying brother (who ALWAYS lie), could (more possibly "would"), lie with his own identity. And the thing is, your answer would only be one question which should positively lead you to the right way. So, what should it be, if not the spoiled answer earlier?
    true, but the given shouldnt have been put into the question in the first place scince it's unrealistic.Real life situations should be put into logic questions.
    so I'm going to assume that the question is purely fiction, and the given is real.
    In which case you/that spoiler would be right.

  7. #67
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    Re: What is Logic? (Logic 101)

    Quote Originally Posted by Comtesse View Post
    Hm. I've heard this riddle many times, but I don't get it.

    Let's see.

    ---------------------------------------------

    If you ask the liar brother - which path would your brother tell me to go? - you would get:

    1) My LIAR brother would tell you to the the RIGHT path.
    2) My TRUTHFUL brother would tell you to take the RIGHT path.
    3) My LIAR brother would tell you to take the LEFT path.
    4) My TRUTHFUL brother would tell you to take the RIGHT path.

    Then you could ask the other brother the same question and he would reply with...:

    1) My LIAR brother would tell you to the the RIGHT path.
    2) My TRUTHFUL brother would tell you to take the RIGHT path.
    3) My LIAR brother would tell you to take the LEFT path.
    4) My TRUTHFUL brother would tell you to take the RIGHT path.

    ...the same thing. So, if they looked the same, and no way of telling the difference, then you would have no idea where to go.

    Or am I not getting something?
    Well,

    You don't need to know which brother is the liar in order to find the answer to the question.

    The reason why the question works is that, by asking one brother what the other would say, the response you get will always be a lie.

    Possibility one: you ask the liar what the truth-teller would say. The liar LIES to you about what the truth-teller would say. The truthteller would tell you the truth (call it T), so the liar tells you the opposite of it (F).

    Possibility two: you ask the truth-teller about what the liar would say. The truth-teller truthfully tells you what the liar's answer would be. But the liar's answer would be a lie. Therefore the truth-teller tells you F.

    Either way, the answer you get is False and all you have to do is choose the other path.
    "I am against religion because it teaches us to be satisfied with not understanding the world" - Richard Dawkins

    "If you could rationalize with Religious people there would be no more Religious people" -Gregory House

  8. #68
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    Re: What is Logic? (Logic 101)

    Quote Originally Posted by dbogjohnson View Post
    true, but the given shouldnt have been put into the question in the first place scince it's unrealistic.Real life situations should be put into logic questions.
    so I'm going to assume that the question is purely fiction, and the given is real.
    In which case you/that spoiler would be right.
    This is a problem (a logical challenge) and the reality could provide something illogical from what it is supposed to be (supposed - based on the given) and the given is part of the problem itself. To come up with an answer, you must logically arrange and consider the points given, with understood definitions, so as to come up with the positive answer.

  9. #69
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    Re: What is Logic? (Logic 101)

    Quote Originally Posted by Allocutus View Post
    Yes, that's possible. But because the liar brother has to lie, he'll lie about what his truth-telling brother would say about which way is the right way to go
    Yes, it is basically what he should say.
    It would make him tricky but still valid to make us think and to lie that he is the honest one. It's a technical possibility.

    But I would like to say that this kind of presumptions, which were given, are of course not really reliable in reality but the basic logic that it requires is a very useful tool to apply and notably remember, to solve or advance problems, simple or complex.

  10. #70
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    Re: What is Logic? (Logic 101)

    Oh.... Thanks for that explanation.

    But, I didn't know the liar ALWAYS lied.
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  11. #71
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    Re: What is Logic? (Logic 101)

    Quote Originally Posted by curious boy View Post
    Yes, it is basically what he should say.
    It would make him tricky but still valid to make us think and to lie that he is the honest one. It's a technical possibility.
    But he's not asked whether he's the honest one. He's asked about what his brother would say. While he can also tell us any number of other things (lies of course), he's really only asked to answer one specific question.

    And we don't care which brother is the honest one. The liar's answer about what his brother would say will always be a lie; he has to lie. The honest brother's answer will always be the truth but it will be the truth about what the liar would say; the truth about a lie. Either way we get the false answer and choose the other path.
    "I am against religion because it teaches us to be satisfied with not understanding the world" - Richard Dawkins

    "If you could rationalize with Religious people there would be no more Religious people" -Gregory House

  12. #72
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    Re: What is Logic? (Logic 101)

    This is a problem (a logical challenge) and the reality could provide something illogical from what it is supposed to be (supposed - based on the given) and the given is part of the problem itself. To come up with an answer, you must logically arrange and consider the points given, with understood definitions, so as to come up with the positive answer.
    true, and in reality you can't assume a person a constant role, you can't define anyone with a 100% chance he/she will lie in real life.So the Question is fictional/ highly unlikely.

  13. #73
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    Re: What is Logic? (Logic 101)

    Quote Originally Posted by Allocutus View Post
    It makes no difference whether the brother you speak to is the liar or the truth-teller. One way or the other, the solution works and will work every time. The question is structured in such a way that no matter which brother you ask you will get pointed to the wrong path
    The question I assume you are referring to,

    "What path would your brother tell me to take to get to my destination?"

    may be a little too open ended to get you pointed to the wrong path every time. Isn’t there more than one possible false answer to this question? An example of an alternative false answer might be “My brother would tell you that neither path will get you to your destination.”. If the liar gave this answer you would be no closer to discovering the correct path.

    Perhaps a more specific question would help eliminate this possibility. Maybe something like,

    “True or false? Your brother would answer ‘true’ to the question ‘True or false? Path A is the best way to my destination.’”

    Though, depending on what you consider a legitimate answer to a question, the liar might still get around this by answering such a question with, “I don’t understand the question”. Assuming the liar really did understand the question, this would be a lie. Whether or not this is a legitimate answer to the specific question being asked is debatable though. I guess it all comes down to defining what is considered a legitimate answer to your question.

  14. #74
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    Re: What is Logic? (Logic 101)

    Quote Originally Posted by Feedback View Post
    The question I assume you are referring to,

    "What path would your brother tell me to take to get to my destination?"

    may be a little too open ended to get you pointed to the wrong path every time. Isn’t there more than one possible false answer to this question? An example of an alternative false answer might be “My brother would tell you that neither path will get you to your destination.”. If the liar gave this answer you would be no closer to discovering the correct path.

    Perhaps a more specific question would help eliminate this possibility. Maybe something like,

    “True or false? Your brother would answer ‘true’ to the question ‘True or false? Path A is the best way to my destination.’”


    That's a very good point. The riddle as I knew it when I was a child was slightly different. It was about 2 guards and 2 doors. One guard stands at either door. One door leads to the gallows, the other to freedom. The question to ask was "If I were to ask you friend if this door leads to freedom, would he affirm?".....an alternative (and slightly less straight forward in terms of methodology) question was "does the guard who always lie stand at the door that leads to freedom?" If the answer is "no" you choose the door at which the guard you asked is standing. If the answer is "yes" you choose the other door.



    Though, depending on what you consider a legitimate answer to a question, the liar might still get around this by answering such a question with, “I don’t understand the question”. Assuming the liar really did understand the question, this would be a lie. Whether or not this is a legitimate answer to the specific question being asked is debatable though. I guess it all comes down to defining what is considered a legitimate answer to your question.
    I think we'd have to assume that each brother/guard has to give a directly responsive (albeit not necessarily true) answer and that each is assumed to be perfectly capable of correctly understanding any coherent question asked. Since they are already compelled to either always lie or always tell the truth, putting that additional restriction as a riddle parameter shouldn't be too much of a problem
    "I am against religion because it teaches us to be satisfied with not understanding the world" - Richard Dawkins

    "If you could rationalize with Religious people there would be no more Religious people" -Gregory House

  15. #75
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    Re: What is Logic? (Logic 101)

    I agree. Adding an additional riddle parameter would fix this problem.

  16. #76
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    Re: What is Logic? (Logic 101)

    Another idea might be asking this tricky question:

    Is the truthful brother standing in the right road?

    If Yes, take that road. Only the liar and the truthful brother who stands in the right road can say this.

    If No, take the other road. Only the liar and the truthful brother who stands in the wrong road can say this.

  17. #77
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    Re: What is Logic? (Logic 101)

    Quote Originally Posted by curious boy View Post
    Another idea might be asking this tricky question:

    Is the truthful brother standing in the right road?

    If Yes, take that road. Only the liar and the truthful brother who stands in the right road can say this.

    If No, take the other road. Only the liar and the truthful brother who stands in the wrong road can say this.
    Indeed. Very much like my two guards in my post above. I didn't propose that because I couldn't recall if our version of the problem involves the brothers actually standing AT the roads (and felt too lazeee to scroll back :D)
    "I am against religion because it teaches us to be satisfied with not understanding the world" - Richard Dawkins

    "If you could rationalize with Religious people there would be no more Religious people" -Gregory House

  18. #78
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    Re: What is Logic? (Logic 101)

    Okay, how about asking this question:

    "What are you going to say if I ask you where is the right road?"

    Both of them will point the right road.

    The honest brother would tell you truthfully. The liar brother would be forced to lie two times, thus, he would point the right road as well.

    So again, regardless of who he was, both will point the right road. So, it is much simpler.

  19. #79
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    Re: What is Logic? (Logic 101)

    Quote Originally Posted by curious boy View Post
    Okay, how about asking this question:

    "What are you going to say if I ask you where is the right road?"
    This is the same as asking "Which is the correct path to take?"

    Let's say that the correct path is "A".

    IF you got the truth brother (you have no way of knowing), he will say "A". If you got the lying brother (you have no way of knowing) he will say "B".

    So, you have 2 choices..."A" or "B". And at this point, you have no way of knowing which is the correct path and which is incorrect. You are still at square one here.

    Both of them will point the right road.
    They point to different roads, not the same one.

    The honest brother would tell you truthfully. The liar brother would be forced to lie two times, thus, he would point the right road as well.
    How will the lying brother answer 1 question, 2 times? That's problem #1. He's not forced to answer a 2nd time (reread the question, perhaps you missed something).

    The 2nd problem, is that the lying brother (according to your answer), would be telling the truth...something that cannot be done by the lying brother.

    So again, regardless of who he was, both will point the right road. So, it is much simpler.
    For reasons explained above, I don't think this will work out for you.

    There's only 1 correct answer...it's in spoiler tags in my response to the question on page 1.
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  20. #80
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    Re: What is Logic? (Logic 101)

    Quote Originally Posted by Apokalupsis View Post
    This is the same as asking "Which is the correct path to take?"

    Let's say that the correct path is "A".

    IF you got the truth brother (you have no way of knowing), he will say "A". If you got the lying brother (you have no way of knowing) he will say "B".

    So, you have 2 choices..."A" or "B". And at this point, you have no way of knowing which is the correct path and which is incorrect. You are still at square one here.


    They point to different roads, not the same one.


    How will the lying brother answer 1 question, 2 times? That's problem #1. He's not forced to answer a 2nd time (reread the question, perhaps you missed something).
    Yes, the lying brother would be forced to lie two times but he wouldn't say the first one. What I mean is that he knows he is going to lie so that he is going to lie again and say that he would say it's A.

    Quote Originally Posted by Apokalupsis View Post
    The 2nd problem, is that the lying brother (according to your answer), would be telling the truth...something that cannot be done by the lying brother.


    For reasons explained above, I don't think this will work out for you.

    There's only 1 correct answer...it's in spoiler tags in my response to the question on page 1.
    He did not tell the truth. The technique is based on the only one question that you ask and on the law the given has set.

    And actually, the question Allocutus and I have secondly mentioned still proves to be effective (read my previous post).

 

 
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