L24_Indirect_and_Disjunctive_Syllogisms

L24_Indirect_and_Disjunctive_Syllogisms - We have learned...

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We have learned about two types of syllogisms so far: The direct syllogism [Latin name: modus ponens], of the form pΛ(p 0 q), q and the transitive syllogism, of the form (p 0 q)Λ(q 0 r), (p 0 r). Now we learn about two more syllogisms: The indirect syllogism [Latin name: modus tollens], of the form (p 0 q) Λ ~q, ~p . Finally, the disjunctive syllogism has the form (pVq) Λ ~p , q .
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Example: I will go to Chicago or you will get $100. I do not go to Chicago. Therefore you will get $100. This is an example of a valid disjunctive syllogism. Example: Every dog is a loyal friend. My pet, Sampson, is not a loyal friend. Therefore Sampson is not a dog. This is an example of a valid indirect syllogism.
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Discuss the following syllogism: Lucy wears red or Julie wears green. Julie wears green. Therefore Lucy does not wear red. Analysis: Let p: Lucy wears red q: Julie wears green. The syllogism has the form (pVq) Λ q, p which is an invalid syllogism.
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Example: Make a valid conclusion from the information p
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This note was uploaded on 10/11/2011 for the course PSYC, PSYC 2076, 2060 taught by Professor Briganti,gustan,perlis,namikas,wheeler during the Spring '10 term at LSU.

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L24_Indirect_and_Disjunctive_Syllogisms - We have learned...

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