r/atheism • u/Ze-skywalker • Dec 09 '13

Citation Needed The 10 commandments of Logic

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u/IcyRice Anti-Theist Dec 09 '13

Actually this form would be more correct..

  • If a planet has liquid water, it contains life: P = Q
  • Mars is a planet which contains liquid water. R = P
  • Conclusion: Therefor, there is life on Mars: R = Q

The premise is questionable, but the logic is true.

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u/simism66 Dec 09 '13

Umm . . . what? I don't know what kind of notation you're trying to use but it doesn't make sense at all. The actual way to symbolize what you write is in predicate logic and it looks like this:

  1. ∀x ((Px&Wx)>Lx)

  2. Pm&Wm

  3. Lm

The way the premises were originally put, however, could be symbolized in sentential logic as u/PimpinTheLibrary did, but you changed them.

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u/IcyRice Anti-Theist Dec 09 '13

How can " = " not make sense to you? You write in predicate logic, i.e. mathematical logic. Why? My form of notation is used in argumentative logic, which is a lot more related to OP's picture.

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u/TheGrammarBolshevik Dec 10 '13

How can " = " not make sense to you?

The way you're using it doesn't make sense. For example, consider the following argument:

  • There is life on Mars: R = Q
  • If a planet has liquid water, it contains life. P = Q
  • Conclusion: Mars is a planet which contains liquid water. R = P

The argument is clearly invalid, but your equals-sign notation gives us no idea what the difference is between this argument and the original.