1. Joined
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    19 May '12 00:46
    Before I present the proof, recall the following. P -> Q is true whenever P is false or Q is true. Recall also that modus tollens is a valid form of argument:

    P -> Q
    Not-Q.
    Therefore, not-P.

    So, then, here is the proof:

    (1) If God does not exist, then it is not the case that if I am evil, I will be punished after I die.
    (2) I am not evil.
    (3) Therefore, God exists.

    😛
  2. Joined
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    19 May '12 01:10
    Originally posted by LemonJello
    Before I present the proof, recall the following. P -> Q is true whenever P is false or Q is true. Recall also that modus tollens is a valid form of argument:

    P -> Q
    Not-Q.
    Therefore, not-P.

    So, then, here is the proof:

    (1) If God does not exist, then it is not the case that if I am evil, I will be punished after I die.
    (2) I am not evil.
    (3) Therefore, God exists.

    😛
    Except that (2) is not the same as the consequent of (1). If I am not evil, then the conditional 'If I am not evil, I will be punished after I die' is trivially true. It's not modus tollens.
  3. Joined
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    19 May '12 01:133 edits
    Originally posted by Conrau K
    Except that (2) is not the same as the consequent of (1). If I am not evil, then the conditional 'If I am not evil, I will be punished after I die' is trivially true. It's not modus tollens.
    I think you made a typo in the antecedent of your conditional.

    At any rate, it is modus tollens. Take another look at the full consequent of (1).
  4. Joined
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    19 May '12 01:17
    Originally posted by LemonJello
    Before I present the proof, recall the following. P -> Q is true whenever P is false or Q is true. Recall also that modus tollens is a valid form of argument:

    P -> Q
    Not-Q.
    Therefore, not-P.

    So, then, here is the proof:

    (1) If God does not exist, then it is not the case that if I am evil, I will be punished after I die.
    (2) I am not evil.
    (3) Therefore, God exists.

    😛
    http://i0.kym-cdn.com/photos/images/original/000/131/351/eb6.jpg?1307463786
  5. Joined
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    19 May '12 01:19
    Originally posted by Zahlanzi
    http://i0.kym-cdn.com/photos/images/original/000/131/351/eb6.jpg?1307463786
    Tell me precisely what is wrong with the proof. I know what the problem is here; do you?
  6. Joined
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    19 May '12 01:281 edit
    Originally posted by LemonJello
    Tell me precisely what is wrong with the proof. I know what the problem is here; do you?
    the only mystery about the "proof" is whether you thought of it as a joke(aka trolling) or you had a brain fart (aka stupid) and you actually believe you came up with something intelligent.


    either way, it is illogical.
  7. Joined
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    19 May '12 01:31
    Originally posted by Zahlanzi
    the only mystery about the "proof" is whether you thought of it as a joke or you had a brain fart and you actually believe you came up with something intelligent.


    either way, it is illogical.
    If it is illogical, then please point out where the logic fails.

    Anyway, I did not come up with this proof. A person much smarter than I came up with it. I think it can be an instructive exercise to try to figure out why it fails.
  8. Joined
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    19 May '12 01:40
    Originally posted by LemonJello
    If it is illogical, then please point out where the logic fails.

    Anyway, I did not come up with this proof. A person much smarter than I came up with it. I think it can be an instructive exercise to try to figure out why it fails.
    instructive exercise? for something this poorly constructed? are you kidding?



    i ask again, are you trolling? the alternative to this might be more embarrassing for you.
  9. Joined
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    19 May '12 01:41
    Originally posted by Zahlanzi
    instructive exercise? for something this poorly constructed? are you kidding?



    i ask again, are you trolling? the alternative to this might be more embarrassing for you.
    I repeat: if it is illogical, then please point out where the logic fails. And please be specific.
  10. Joined
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    19 May '12 01:46
    Originally posted by LemonJello
    I repeat: if it is illogical, then please point out where the logic fails. And please be specific.
    i fed the troll. i am ashamed.

    please feel free to congratulate yourself for provoking me into 3 posts in a trolling thread.
    or feel free to assume i am ignorant of logic and jealous of your awesome intellect if you are sincere in wanting to debate this.
  11. Joined
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    19 May '12 01:49
    Originally posted by Zahlanzi
    i fed the troll. i am ashamed.

    please feel free to congratulate yourself for provoking me into 3 posts in a trolling thread.
    or feel free to assume i am ignorant of logic and jealous of your awesome intellect if you are sincere in wanting to debate this.
    So you are unwilling (or unable) to back up your claim that the proof I presented is illogical?

    You get a FAIL.
  12. Joined
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    19 May '12 02:012 edits
    Originally posted by LemonJello
    I think you made a typo in the antecedent of your conditional.

    At any rate, it is modus tollens. Take another look at the full consequent of (1).
    Basically what I mean to say is that the conditional is trivially false and modus tollens does not apply.

    As I see it, there are three propositions:
    P -- God exists
    Q -- I am evil
    R -- I will be punished after I die.

    So the proof runs like this:

    (1) ~P --> ~(Q-->R)
    (2) ~Q
    Therefore,
    (3) P.

    If ~Q, however, then Q-->R is trivially true, so the consequent ~(Q-->R) is trivially false.

    Under the same logic, you can mount a proof of anything. Basically it's a failure of relevance logic, like saying 'If the world will end, then 2+2 =4'.
  13. Joined
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    19 May '12 02:143 edits
    So, as far as propositional calculus goes, it is logical.

    Reductio ad absurdum:

    (1) ~P --> ~(Q-->R)
    (2) ~Q
    Therefore,
    (3) ~P. (i.e. God does not exist)

    From (1)
    ~~P or ~(Q-->R)
    so,
    P or (Q and ~R)

    But (Q and ~R) contradicts (2) ~Q.

    But P contradicts (3) ~P.

    I think the failure must be relevance, the fact that we are dealing with truth triviality. We get the same triviality if we assert R, I will be punished after I die. So if I will be punished after I die, then (Q-->R) is trivially true and so ~(Q-->R) false and therefore ~P is false, so P, God must exist.
  14. Joined
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    19 May '12 02:201 edit
    Originally posted by Conrau K
    Basically what I mean to say is that the conditional is trivially false and modus tollens does not apply.

    As I see it, there are three propositions:
    P -- God exists
    Q -- I am evil
    R -- I will be punished after I die.

    So the proof runs like this:

    (1) ~P --> ~(Q-->R)
    (2) ~Q
    Therefore,
    (3) P.

    If ~Q, however, then Q-->R is trivially ...[text shortened]... asically it's a failure of relevance logic, like saying 'If the world will end, then 2+2 =4'.
    Yes, very good. You've proven yourself much more worthy than our friend Zahlanzi.

    I do not think the problem here involves any mis-application of modus tollens. But I would agree that the problem is related to the subject of relevance logic. The problem here must lie in how it treats an indicative conditional like 'If I am evil, I will be punished after I die' and bases it in the truth functionality of a material conditional.
  15. Joined
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    19 May '12 02:23
    Originally posted by LemonJello
    Yes, very good. You've proven yourself much more worthy than our friend Zahlanzi.

    I do not think the problem here involves any mis-application of modus tollens. But I would agree that the problem is related to the subject of relevance logic. The problem here must lie in how it treats an indicative conditional like 'If I am evil, I will be punished after I die' and bases it in the truth functionality of a material conditional.
    The problem here must lie in how it treats an indicative conditional like 'If I am evil, I will be punished after I die' and bases it in the truth functionality of a material conditional.

    Yes, that sums it up. It was nothing to do with modus tollens per se. Thank you for that interesting piece of logic.
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