1. Logical Fallacies

2. Definition & Facts Defects that weaken arguments Common in
politics and
advertisements
Often very
persuasive

3. Don’t weaken your argument with faulty reasoning!

4. When you attempt to employ logic to support claims in your papers, your reasoning is sometimes weakened because you are presenting fallacious arguments.
It is important for you to be able to identify and eliminate fallacies in your writing.

5. Check this out! This fallacy is very common in advertising,
as in this simple
example.

6. Unchanged Since 1899
(Reader's Digest, March, 1999, p. 15)

7. Hershey’s Advertisement
Appeal to Tradition 
Any argument that defends a behavior
or choice by pointing out that the
behavior or choice is a longstanding
practice. Unfortunately, many foolish
and destructive behaviors are also
very traditional, such as slavery,
forced prostitution, and punishing
children by hitting them with
belts. 

8. What the heck does this mean?
bandwagon

9. bandwagon:
logical fallacy in which the writer
uses the argument that because
everyone believes in something, it
must be true.

10. “I’m going to the party because all my friends are going!”
Example
“I’m going to the party because all my friends are going!”

11. What the heck does this mean?
begging the question

12. begging the question:
logical fallacy in which the writer
presents an assertion that simply
restates the point just made

13. Example
"Exposure to asbestos is carcinogenic because it causes cancer.”

14. What the heck does this mean?
ad hominem

15. ad hominem:
logical fallacy in which the writer
attacks the person who presents
the issue rather than deal logically
with the issue itself.

16. Example
"Ignore what Professor Doe says about the origins of the Old Testament. I happen to know that Doe is an atheist."

17. What the heck does this mean?
either-or fallacy

18. either-or fallacy:
logical fallacy in which the writer
states that only two alternatives
exist when in fact there are more
than two.

19. Example
“Caldwell Hall is in bad shape. Either we tear it down and put up a new building, or we continue to risk students’ safety. Obviously we should not risk anyone’s safety, so we must tear the building down."

20. What the heck does this mean?
red herring

21. red herring:
logical fallacy in which the writer
dodges the real issue by drawing
attention to an irrelevant issue
(ignoring the question).

22. Example Real Example: Analysis:
"No, no, he's a friend of mine. He's not a moron at all -- he's a
friend. I had a good time with him today."
Canadian Prime Minister Jean Chretien, responding to
reports that his chief spokesman had called President
George W. Bush a moron. (Newsweek, 2 Dec. 2002)
Analysis:
Perhaps it's true that Bush is his friend. Perhaps it's
true that they had a good time together. What has that
information got to do with answering the charge that
Bush is a moron? Chretien is changing the subject
instead of talking about Bush's intelligence.