And the next U.K. Prime Minister will be?

Discussion in 'Free Thoughts' started by Speakpigeon, Jul 14, 2019.

?

Is the argument valid?

Poll closed Aug 11, 2019.
  1. Yes, the argument is valid

    1 vote(s)
    25.0%
  2. No, the argument is not valid

    1 vote(s)
    25.0%
  3. I don't know

    1 vote(s)
    25.0%
  4. The argument doesn't make sense

    1 vote(s)
    25.0%
  1. Speakpigeon Valued Senior Member

    Messages:
    1,033
    Here is a "U.K. current affairs" argument.

    P1 - Jeremy Corbyn is not Boris Johnson;
    P2 - Boris Johnson is not Jeremy Hunt;
    P3 - Jeremy Hunt is not Jeremy Corbyn;
    P4 - The next U.K. Prime Minister will be either Boris Johnson or Jeremy Hunt;
    P5 - The next U.K. Prime Minister will be Jeremy Corbyn;
    C - Therefore, the next U.K. Prime Minister will be Boris Johnson.​

    Thank you to say whether you consider this argument valid or not.

    Thank you to abstain from commenting before you voted.
    EB
     
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  3. Beer w/Straw Transcendental Ignorance! Valued Senior Member

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    I'd say, Hitler, but I don't know if this guy, I've just heard of, is legally allowed for some reason to actually run.
     
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  5. sweetpea Valued Senior Member

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    Current? You do know it's a two horse race?
     
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  7. James R Just this guy, you know? Staff Member

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    P1 and P5 are inconsistent with C, therefore invalid.

    That's not the only problem.
     
  8. exchemist Valued Senior Member

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    Trying to win a prize for the fastest operation of Godwin's Law?

    Please Register or Log in to view the hidden image!

     
  9. Speakpigeon Valued Senior Member

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    1,033
    You mean that P1 and P5 are invalid?
    Go on. What are the other problems?
    EB
     
  10. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

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    8,429
    Be said that I don’t know, because it rather depends on how one is defining what it means to be valid.
    In the most usually accepted sense (I.e. classical logic) of truth preservation, then the argument is valid, as any conclusion built from contradictory premises preserves the truth. It’s a quirk of the definition of logical validity that is most commonly used, and is known as deductive explosion. Ex contradictione quodlibet.

    However, if you mean in a sense akin to the conclusion actually being justified by the premises, then no, it is not valid, again because the premises are contradictory.

    And since the poll asks “is the argument valid?” without indicating what understanding of validity you are asking about, the closest option is “I don’t know”.
     
  11. geordief Valued Senior Member

    Messages:
    1,029
    The conclusion does not follow if #5 is correct.What am I missing? (#5 doesn't follow from the earlier premises-in fact it is impossible* if #4 is correct)

    *depending on the precise meaning of "either" in #4 (exclusively "either" or "either " among other possibilities and so meaningless)
     
  12. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

    Messages:
    8,429
    You’re not missing anything. It’s a near-identical poll he’s posted in the past involving assessment of a logical argument with contradictory premises, and whether one views it as valid or not. It’s basically a semantic issue of how one interprets validity, whether one uses a formal definition (e.g. a deductive argument is valid if and only if it takes a form that makes it impossible to for the premises to be true and the conclusion nevertheless false) or whether you take a more casual/layman approach and view validity on whether the conclusion follows from the premises.

    If the former then it is valid, if the latter then it is probably not considered valid.
    As interesting as all that is.
     
  13. Speakpigeon Valued Senior Member

    Messages:
    1,033
    OK. Premises are implicitly assumed correct. So, yes, premise 5 is assumed correct, however unlikely the perspective may appear to be.
    I don't think you've missed anything. It is just possible to make contradictory statements, just as it is possible to make otherwise obviously false statements. You won't look good if you do that, obviously, but I'm not trying to look good.
    I'm quite sure "either" is exclusive. It implies that one and only one of the possibilities identified in the same clause is true.
    The only debate is whether you can have more than two possibilities...
    That's what dictionaries say.
    Thank you to cast your vote if you haven't already.
    EB
     
  14. Speakpigeon Valued Senior Member

    Messages:
    1,033
    Fair enough but the question asked is explicitly whether you consider it valid. I would hope you know whether you do or not.
    EB
     
  15. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

    Messages:
    8,429
    Whether I consider it valid depends on which version of the word "valid" I am considering. Since I am capable of considering both, it is a false dilemma to have to pick one or the other.
     
  16. Speakpigeon Valued Senior Member

    Messages:
    1,033
    So, how do you decide which notion of validity should apply? On a whim?
    EB
     
  17. James R Just this guy, you know? Staff Member

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    No. I mean what I wrote.
     
  18. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

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    8,429
    Context. What context would you like me to consider? If none then the answer I gave should suffice for you. If the context is simply "pick one or the other" then it might as well be decided on a whim, or a coin toss, because both are justified.
     
  19. Speakpigeon Valued Senior Member

    Messages:
    1,033
    Yeah. What you actually wrote is that P1 and P5 are invalid. "Inconsistent therefore invalid".

    So, I now I have to suppose contrary to what you write here that what you really mean is not what you wrote but that the argument or the conclusion are invalid because the premises are inconsistent.

    You sure don't like to make it easy.

    Did you cast a vote?
    EB
     
  20. Speakpigeon Valued Senior Member

    Messages:
    1,033
    How asking whether you consider the argument valid or not suggests two notions of validity? What is even remotely suggesting a mathematical context here?
    Wait. Never mind.
    EB
     
  21. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

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    8,429
    Actually he wrote "inconsistent with C, therefore invalid".
    While there is some clear ambiguity in his statement, to most people who aren't simply looking for a fight this would be interpreted as meaning that since P1 and P5 are inconsistent with C, the argument is therefore invalid. The ", therefore invalid" being his answer to the question you posed, the comma seeming to promote that interpretation rather than the one you had initially gone with (of P1 and P5 being inconsistent with C and therefore P1 and P5 being invalid). Had he not included the comma then your interpretation would be more reasonable to take, but even then, the two alternative interpretations would be clear enough such that, given the context, the intended interpretation would be still be obvious. To anyone not looking for confrontation, that is.
    That is what he wrote. You just have interpreted it differently. Admittedly it can be considered ambiguous, but unless one is being particularly belligerent the meaning intended is quite obvious.
    I thought it was easy enough to understand him. I would hazard a guess that most would.
     
  22. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

    Messages:
    8,429
    What you ask doesn't need to suggest two: there are two, at least. But that said, you set out the argument in a formal manner which suggests you are referring to a formal definition of valid. But you have asked this (type of contradictory premises) question before and seemed happy that people also considered non-formal definitions.
    Too late.
     
  23. Speakpigeon Valued Senior Member

    Messages:
    1,033
    My argument is couched entirely in everyday language and there's nothing in my post that suggests I was interested in something other that whether you consider the argument valid. This is indeed how most people take it. The only people who don't are people with a training in mathematical logic because due to their training they are no longer able to decide for themselves whether the argument is valid.
    I guess if I asked you whether the law is just, you would answer yes because the law says the law is just.
    EB
     

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