Review - (F H) need f or h to be false 1 st try to prove...

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Review Need to be able to: Determine whether an argument is valid or invalid If argument is invalid, then you should be able to assign truth values so as to arrive at an interpretation demonstrating its invalidity If an argument is valid, you should be able to construct a direct proof (given premises and conclusion, derive conclusion) If an argument is valid, then you should be able to construct an indirect proof (assume negation of conclusion, end up with contradiction) Trick to direct/indirect: indirect proofs normally faster Examples: E F (G H) 1 st : Therefore (E v G)need e or g to be true
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Unformatted text preview: (F H) need f or h to be false 1 st try to prove invalidity E, F, G, H F, F, T, T Invalid Indirect proofs assume negation, derive contradiction B [(O v ~O) (T v U)] U ~(G v ~G) ~(B T) IP ~(~B v T) Imp, 3 ~~B ~T 4, DeM ~~B 5, Simp B 6, DN (O v ~O) (T v U) 1, 7 MP B v ~O 7, Add ~O v B 8, Comm O B imp, 10 O (OB) 11, Abs ~O v (OB) 12, Impl lj(~O v O) (~O v B) Dist, 13 ~O v O 14, Simp O v ~O comm, 15 T v U MP 16, 8 ~T ~~B comm, 5 ~T Simp, 18 U 17, 19 DS ~(G v ~G) MP 2, 20 ~G ~~G...
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This note was uploaded on 03/16/2011 for the course PHIL 045 taught by Professor Hopper during the Fall '07 term at GWU.

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Review - (F H) need f or h to be false 1 st try to prove...

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