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Disjunctive Syllogism

Date: 09/25/98 at 10:51:45
From: Lauren Ray
Subject: Disjunctive Syllogism

I am enrolled in a Elementary Logic and Set Theory class, and we have 
an assignment to find out definitions of the words: Modus Ponens, 
Modus Tollens, and Disjunctive Syllogism. I have already found the 
first two, but am stuck on the last one. So my question is, what does 
it mean?  

Thank you,

Date: 09/25/98 at 11:28:48
From: Doctor Mike
Subject: Re: Disjunctive Syllogism

Hi Lauren,  
See Stefan Waner and Steven R. Costenoble's "Introduction to Logic" on 
the Web. It has the definition of Disjunctive Syllogism and other logic 
The disjunctive syllogism is  (P v Q) and notQ --> P. In words:

   "If one or the other is true, and one of them is false, the other 
   must be true."

Here is an example:

   -  Given: Either Congress meets in Washington D.C. OR pigs can fly.
   -  Given: Scientific evidence shows conclusively that pigs cannot 
   -  Conclusion: Congress meets in Washington D.C.   
I hope this helps. 
"Thanks for writing."  OR  "Pigs can fly."
- Doctor Mike, The Math Forum
Associated Topics:
High School Definitions
High School Logic

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