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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,
Lauren
```

```
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
terms.

http://www.hofstra.edu/~matscw/logic/logic4.html

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
fly.
-  Conclusion: Congress meets in Washington D.C.

I hope this helps.

"Thanks for writing."  OR  "Pigs can fly."

- Doctor Mike, The Math Forum
http://mathforum.org/dr.math/
```
Associated Topics:
High School Definitions
High School Logic

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