Examples 7.4

Examples 7.4 - Examples 7.4 Rules of Replacement II . . ....

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Examples 7.4 Rules of Replacement II . . . Transposition (Trans) (A B) :: (~B ~A) This one ought to make sense if you think about it for a second. If it’s true that ‘If it rains, then the game is cancelled, then it certainly has to be true that ‘If the game is not cancelled, then it didn’t rain’. Or, you could think of it as modus tollens following from modus ponens (and vice versa). This rule will be fairly important—it’s always nice to be able to change those conditionals around to derive new things. Material Implication (Impl) (A B) :: (~A v B) Again, just thinking about this one will make it clear. If it’s true that ‘if it rains then the game is cancelled’, then it has to be true that ‘either it doesn’t rain or the game is cancelled’. This is easily my favorite rule of them all. I think it’s EXTREMELY useful. Usually, I can solve most complicated derivations by appeal to this rule and just a few others (like simplification, conjunction, disjunctive syllogism, etc.). I DEFINITELY
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This note was uploaded on 05/04/2008 for the course PHIL 2203 taught by Professor Barrett during the Spring '08 term at Arkansas.

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Examples 7.4 - Examples 7.4 Rules of Replacement II . . ....

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