Validity of a simple logical argument

Discussion in 'General Philosophy' started by Speakpigeon, Jan 23, 2019.

?

Is the argument valid?

This poll will close on Feb 22, 2019 at 2:00 PM.
  1. No

    54.5%
  2. Yes

    45.5%
  3. I don't know

    0 vote(s)
    0.0%
  4. The argument doesn't make sense

    0 vote(s)
    0.0%
  1. Speakpigeon Registered Senior Member

    Messages:
    761
    This is a poll on the logical validity of the following argument:

    Is this argument logically valid?
    Either way, why?
    EB
     
    Last edited: Jan 23, 2019
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  3. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

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    Please can you state why you are asking? What is the purpose of the poll? If it is to simply see who thinks it is valid, not valid or one of the other options, please can you enlighten us as to the purpose of your inquiry.
    To continually post what seem to be nothing more than your school homework is not really engendering actual discussion, is it. So, please, explain yourself.
     
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  5. Write4U Valued Senior Member

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    9,467
    Perhaps we should start with the premise, before we analyze the logic.

    IMO, the premise is fatally flawed and any logical processing of the facts will result in garbage. Garbage in....garbage out.

    This is your premise:
    Joe is either a squid or a giraffe
    Joe is an elephant.

    Therefore Joe is ?????

    Answer: Joe is an elephant! An elephant is not a squid or a giraffe.
    Therefore: Joe cannot be a squid or a giraffe.

    The statement (premise) that Joe is either a squid or a giraffe is false.
     
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  7. Speakpigeon Registered Senior Member

    Messages:
    761
    This argument is very simple so we should all get to agree as to its validity. I started off with the Conscious mind argument, and that turned out to be well above what people here could understand without the benefit of formal logic, save for two people I think. So, I'm forced to make it easier. And there is an interesting point about it. I just lifted it from a website where the explanation provided is bogus, so, there's something to learn and, again, we should normally agree as to validity because it is such a simple example. And no modal logic in this case, so what's there to stop you?
    Irrespective of me, you should be able to arrive at a consensus as to validity.
    My purpose is very simply to understand why people are apparently unable to let their intuitive sense of logic do the work and perhaps learn to frame arguments so that more people can understand.
    EB
     
  8. Speakpigeon Registered Senior Member

    Messages:
    761
    You're not addressing the topic. The question is as to validity, not soundness.
    Here is my definition of validity:
    EB
     
  9. Write4U Valued Senior Member

    Messages:
    9,467
    That's the problem. The premise of the argument is prima facie not valid.
    Hmm,
    here I thought that logical soundness and validity are fruits of the same tree.

    I did address the topic and gave the same answer as you just did. I just stated it differently.
    Am I required to quote your answer verbatim, else it is wrong?
    The premise of the question is untrue, it is unsound, it is not valid, it is a piece of trash. The conclusion can only be false. Garbage in --> Garbage out.
    It should not be asked by a person with sound logical mental processes.

    Try to pull this trick with mathematics......"error"........

    Please Register or Log in to view the hidden image!

     
    Last edited: Jan 23, 2019
  10. Speakpigeon Registered Senior Member

    Messages:
    761
    Premises are either true or false, not valid or invalid.
    Then, what you mean is that the premises are false.
    No. If the premises are false, then conclusion may well be true. Joe may well be a squid. But that's not the question.
    To assess validity, you have to assume the truth of the premises.
    No.
    Garbage in, garbage out only if the argument is valid.
    That's kindergarten level. You should try to understand logic.
    Sorry!
    And maybe you're assuming too much.
    EB
     
  11. Write4U Valued Senior Member

    Messages:
    9,467
    How many times do I have to tell you that before you understand what I am saying. Don't cloak your argument in semantics.
    The premise on which the exercise is based is false. A person cannot be two different things at the same time.
    The problem already posits a conclusion. Joe is an elephant. Therefore he cannot logically be a squid or a giraffe. End of story.
     
  12. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

    Messages:
    8,055
    Okay, I'll bite.
    It's valid.

    It certainly doesn't seem to be on the surface, though, and indeed if you only consider the syllogism made up of premises 3, 5, and the conclusion, then that syllogism would be invalid.
    However, if one considers an argument valid "if, and only if, it is impossible for (all) the premises to be true and the conclusion at the same time to be false" (or words to that effect), then any argument with contradictory premises, as yours is, is to be considered valid. It's a rather counter-intuitive result of such a definition of validity. Since it is not possible for all the premises to be true (some being contradictory) it must therefore be impossible for all the premises to be true. At that stage you can deem any such argument valid, irrespective of whether the conclusion is true or false.
     
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  13. Baldeee Valued Senior Member

    Messages:
    1,478
    Doh!
    Beat me to it.
     
  14. Write4U Valued Senior Member

    Messages:
    9,467
    IMO, the premise is false under both definitions. It asks for an illogical conclusion both ways.
     
  15. Write4U Valued Senior Member

    Messages:
    9,467
    IMO, validity must have a value. When the resulting value is contradictory to the allowable values established in the premise, it is invalid.

    In this case Joe is identified as being an elephant and thus cannot ever be also a squid or a giraffe.

    Any other logical mental gymnastics are a waste of time, IMHO.
     
  16. Baldeee Valued Senior Member

    Messages:
    1,478
    You have a slight misunderstanding of validity, it seems.
    Per wiki (as good as any place for a definition): "an argument is valid if and only if it takes a form that makes it impossible for the premises to be true and the conclusion nevertheless to be false."
    Contradictory premises makes it impossible for all the premises to ever be true at the same time.
    Therefore an argument with contradictory premises satisfies the requirements of a valid argument.
     
  17. iceaura Valued Senior Member

    Messages:
    28,052
    As would any argument in which the conclusion is always true.

    The sticking point in that case would be the word "therefore".
     
  18. RainbowSingularity Valued Senior Member

    Messages:
    1,870
    no
    basing a claim on a supposition as a cause and effect process is applying a false mathematical value to the process of claimed philosophical logic.

    leap-frogging" from one ideological theory to a false claim of fact.
    this is not logic.
    this is attempted con(per)version of logic.
     
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  19. Write4U Valued Senior Member

    Messages:
    9,467
    A valid argument is not necessarily logical and a logical argument is not necessarily valid.

    One can have a valid logical argument based on a false premise, which invalidates the argument.

    You cannot cherry-pick the argument and parse it into logically valid and logically invalid parts.

    A valid logical argument either yields a valid logical result of "true" or "not true".

    An invalid logical argument always yields a result of "not true".

    And if anyone wishes to dispute this, you can begin by explaining how an elephant can logically be a squid or a giraffe at the same time.

    Therefore, somewhere in the proposition there is a logical flaw, which invalidates the argument. And we know where that happens, no?

    Joe is an elephant and therefore NOT a squid or a giraffe.
    Therefore the answer that Joe is a giraffe is logically false (not true). He is an elephant.
     
    Last edited: Jan 24, 2019
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  20. Baldeee Valued Senior Member

    Messages:
    1,478
    No sticking point for determining validity, though, only in terms of our intuition regarding whether it is valid or not.
    Such an argument, with a necessarily true conclusion, would be valid.
    Something is invalid if it is possible for the premises to be true and the conclusion nonetheless to be false.
    Something is valid if it is impossible for the premises to be true and the conclusion nonetheless to be false.
    When you have a necessarily true conclusion (i.e. "always true") then it is impossible for the premises to be true and the conclusion nonetheless to be false.
    Thus valid.

    Many might think that such an argument would be invalid because the conclusion does not seem to follow deductively from the premises.
    It's non-intuitive, granted, but it's because validity is a matter of the preservation of truth: i.e. the impossibility of having true premises and a false conclusion.
    An argument with contradictory/inconsistent premises is valid because you can never have all the premises being true - thus it is impossible to have true premises, irrespective of the conclusion.
    An argument with a necessarily true conclusion is valid because the conclusion is always true - thus you can never have a false conclusion.

    Whether such arguments have any value, however, is another matter.
    Most would dismiss such arguments, however, since their validity is not dependent upon the relationship between premises and conclusion.
    But they are nonetheless valid.
     
  21. Baldeee Valued Senior Member

    Messages:
    1,478
    What do you mean by the word "logical"?
    Do you mean "of logic"?
    The truth or otherwise of a premise does not itself invalidate an argument.
    All dogs are cats
    All cats are mice
    Therefore all dogs are mice.
    This is a valid argument - it is impossible for the premises to be true and the conclusion to be false.
    As you can see, it has no bearing on our reality.
    The premises are untrue, the conclusion untrue, as far as our world goes.
    But if there was a world where the premises were true, it would be impossible for the conclusion to be false.
    That is why the argument is valid.
    So validity doesn't mean that the premises are true, only that if we accept the premises as true then it is impossible for the conclusion to be false.
    An untrue premise in an otherwise valid argument makes the argument unsound.
    So my example above is rather unsound.
    Well, you can, especially if there happen to be irrelevant premises.
    But that was not the reason I did so, but rather to show that on the face of it, by doing so, you might conclude that the argument was invalid.
    No, a valid logical argument preserves the truth from premises to conclusion.
    I.e. it is valid if it is impossible for the premises to be true yet the conclusion false.
    I'm somewhat unsure of what you mean by "result of true or not true".
    Do you mean that you think in an invalid logical argument the conclusion is always not true / false?
    If so, the argument above has a false conclusion (unless you think dogs are mice??) but it is valid.
    It can't.
    But that doesn't make the argument invalid.
    Being two things at once is also quite possible: one can be a supporter of a football team and a member of the Republican party.
    In logical arguments, validity is all about the preservation of truth through the form of the argument.
    Anything to do with how the premises stack up in reality is a matter of soundness (assuming the argument valid).
    The argument is a pile of hooey, for sure, and useless, because it has contradictory premises.
    But it is valid.
    But it's validity in this case is nothing to do with the deductive relationship between premises and conclusion but because the argument is truth preserving.
    In this instance it is truth preserving precisely because the premises can never all be true.
    Out of curiosity, why are you going with that particular premise and not the one that says that Joe is either a squid or a giraffe?
     
  22. RainbowSingularity Valued Senior Member

    Messages:
    1,870
    'terms' ?

    appologies, bit tired so editing as i go
    is preservation capable by procuring invalid fact ?
    holds no fact because of why ?
    the last thing said ?
    thus only the last posit remains logical ?
     
    Last edited: Jan 24, 2019
  23. Speakpigeon Registered Senior Member

    Messages:
    761
    There are two premises. Which one are you talking about? You need to be specific when you express yourself. Don't cloak your meaning into foggy semantics.
    It's a logical argument, not an experiment to establish empirical results.
    So, you can't assume anything on top what the premises say. So, you can't just assume that a person cannot be two different things at the same time.
    And that's no even true.
    For example, a person maybe tall and French. That's two different things and at the same time.
    Sorry, I can't comment because you haven't voted. Vote first, comment after.
    EB
     

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