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Bee_see

  • one year ago

The following argument is valid: If Superman were willing and able to prevent evil, he would do so. If Superman were unable to prevent evil, he would be impotent; if he were unwilling to prevent evil, he would be malevolent. Superman does not prevent evil. If Superman exists, he is neither impotent nor malevolent. Therefore, Superman does not exist.

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  1. Bee_see
    • one year ago
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  2. Bee_see
    • one year ago
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    @FibonacciChick666

  3. FibonacciChick666
    • one year ago
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    Ok, I'd do a truth table

  4. FibonacciChick666
    • one year ago
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    P is the if part of each statement Q is the then. Write each sentence as a P implies Q. Then negate each. And use the final statement to say well since there is evil, superman can't exist

  5. Bee_see
    • one year ago
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    |dw:1444012942048:dw|?

  6. FibonacciChick666
    • one year ago
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    more like P-->~Q uh contrapositive I think? Sorry it has been like 4 years since logic. But let me work on this. It will help me with the test I'm studying for

  7. FibonacciChick666
    • one year ago
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    SO my first thought, If sup exist then he's not imp. and he's not malev.

  8. Bee_see
    • one year ago
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    Hmm, I used the (p imples q) implies (not p or q) table and I got all truth...I want to use the rules of inference though instead of the truth tables. And I'm not sure how.

  9. FibonacciChick666
    • one year ago
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    So, since sup can't prevent evil there exists evil--> sup would prevent it but he doesn't-->imp. and malev. BUT that is a contradiction

  10. Bee_see
    • one year ago
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    (p implies q) bi conditional statement (not p or q) *

  11. FibonacciChick666
    • one year ago
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    and or malev**

  12. Bee_see
    • one year ago
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    how would you show that though using the rules of inference. I'm supposed to do a table.I have the premises like this: Superman is willing to prevent evil(W), superman is able to prevent evil (A), superman prevents evil(P), superman is impotent I, superman is malevolent (M), and superman exists(X).

  13. Bee_see
    • one year ago
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    |dw:1444013971882:dw|

  14. FibonacciChick666
    • one year ago
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    I haven't seen that style before, but my basic argument is, there is evil, it isn't prevented sup isn't I or M --> no sup

  15. FibonacciChick666
    • one year ago
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    So let's put it into words, it's essentially a contradiction proof

  16. FibonacciChick666
    • one year ago
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    SO I'm looking at these inference rules(Gosh they would have been helpful to see before....Thanks BA-NOT)

  17. FibonacciChick666
    • one year ago
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    https://en.wikipedia.org/wiki/List_of_rules_of_inference

  18. FibonacciChick666
    • one year ago
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    so this argument is case analysis I think

  19. FibonacciChick666
    • one year ago
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    ugh, let me get someone smart here. @dan815 can you fix my mess please?

  20. Bee_see
    • one year ago
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    This is how the professors wants it to look if anyone can help:

  21. dan815
    • one year ago
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    sry im here

  22. dan815
    • one year ago
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    are you still working on this The following argument is valid: If Superman were willing and able to prevent evil, he would do so. If Superman were unable to prevent evil, he would be impotent; if he were unwilling to prevent evil, he would be malevolent. Superman does not prevent evil. If Superman exists, he is neither impotent nor malevolent. Therefore, Superman does not exist.

  23. FibonacciChick666
    • one year ago
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    yea

  24. dan815
    • one year ago
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    super man is neither impotent nor malevolent

  25. dan815
    • one year ago
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    superman does not prevent evil, so superman is malevolent, so superman cannot exist

  26. Bee_see
    • one year ago
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    I have some solutions, but I don't understand then. So for example, after writing all the premises, the person used modus tollens 5 and 4. (5 being not p and 4 being W and A implies p)...I'm not sure how the person knew that modus tollens had to be used.

  27. dan815
    • one year ago
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    hmm lemme see

  28. dan815
    • one year ago
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    just 1 little thing that might come up

  29. dan815
    • one year ago
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    superman does not prevent evil means, either there was no evil to prevent, or he was unable to prevent evil

  30. dan815
    • one year ago
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    but if they say does not prevent evil, that means evil must have took place for him to not prevent it

  31. Bee_see
    • one year ago
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    then the person said not W or not A (I'm not sure what rules was used), then M or I (modus ponen....not sure which options). Then not (not M and not I). Came the conclusion that not X. Superman doesn't exist.

  32. dan815
    • one year ago
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    not willing and not able right

  33. Bee_see
    • one year ago
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    |dw:1444015956617:dw|

  34. dan815
    • one year ago
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    okay lemme see

  35. dan815
    • one year ago
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    um wait is upside down V or or and

  36. dan815
    • one year ago
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    because not P should be not (W or A) and W and A --> P but they are using the same operators

  37. Bee_see
    • one year ago
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    V is or.

  38. Bee_see
    • one year ago
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    ^ is and.

  39. dan815
    • one year ago
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    okay then isnt there a mistake in there

  40. dan815
    • one year ago
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    yep looks good!

  41. dan815
    • one year ago
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    because not (W or A ) = W and A so it ha to be W and A =>P there

  42. Bee_see
    • one year ago
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    can you explain the solution? what rules of inference were used and how?

  43. dan815
    • one year ago
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    what do u mean what step is confusing u

  44. Bee_see
    • one year ago
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    the last 6 steps...why use modus tollens for 5 and 4?

  45. dan815
    • one year ago
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    |dw:1444016813628:dw|

  46. dan815
    • one year ago
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    okay there are 2 main ones u need to know

  47. dan815
    • one year ago
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    u can see from truth tables

  48. dan815
    • one year ago
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    |dw:1444016995835:dw|

  49. dan815
    • one year ago
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    this proves not (A and B) = not a or not b

  50. dan815
    • one year ago
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    similiary u can show that not (A or B) = not A and not B

  51. dan815
    • one year ago
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    |dw:1444017343621:dw|

  52. dan815
    • one year ago
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    so these 2 transformations are justified, does that clear it up?

  53. Bee_see
    • one year ago
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    what rules were used to do the last 4 steps?

  54. dan815
    • one year ago
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    well we showed how they are equivalent with the truth table

  55. dan815
    • one year ago
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    its just an identity we just showed so its justified

  56. Bee_see
    • one year ago
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    My professors wants something like this:

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  57. dan815
    • one year ago
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    |dw:1444017601337:dw|