LOGICAL FALLACIES
Logical Fallacies are arguments based on faulty reasoning. They often appear true at
first, but do not hold up to scrutiny. Look for these fallacies whenever you listen to others’
arguments and avoid them in your own writing. Illogical arguments are unpersuasive even
when they express the truth, and your goal in writing is to be persuasive.
Example of a truth reached by faulty reasoning:
All men are mortal; Socrates is mortal; therefore, Socrates is a man.
Notice in this example that, while it is true that Socrates is a man, this truth is
not proven by the bad syllogism. It is not enough to be right, but you must
also be logical.
The following are but a few of the most common logical fallacies.
Post Hoc Reasoning: an assumption that because event A preceded event B,
event A caused event B
Example: There has been a rise in youth violence since the invention of the computer
game; therefore, computer games must promote youth violence.
Ad Hominem Attack: an attack on a person rather than on his or her ideas
Example: We cannot trust the congressman’s crime bill because he was once arrested
for DUI himself.
Generalization: a conclusion based on inadequate data
Example: In a study of six Sosumi coupes, two had bad windshield wipers; therefore the
Sosumi coupe is a lousy car.
Using Anecdotal Evidence: a generalization based on limited personal
experience or on hearsay; remember, the plural of anecdote is not data.
Example: I once saw a panhandler get into a really nice car and drive off; therefore all
panhandlers are really wealthy con artists.
Circular Logic or Tautology or Begging the Question: an argument that is
repeated, usually by rephrasing rather than expanding upon the argument
Example: Television rots your brain because when you watch it, your cognitive functions
begin to deteriorate.
Oversimplification or Reductive Reasoning: a misrepresentation of a
complex concept by reducing it to overly limited terms
Example: Einstein’s theory of relativity can be summed up in one sentence: everything
is relative.
Ignoring or Dismissing Opposing Arguments or Evidence: just what it
sounds like
Example: There is no global warming because some scientists deny that it exists.
Common Sense Argument: an appeal to a reader’s common sense or to
common assumptions
Example: Everyone knows that blondes have more fun.
Bad Syllogism: an allegedly deductive assertion based on three statements of
paired terms
Example: Most birds can fly; a sparrow can fly; therefore, a sparrow is a bird.
Faulty Premise: an argument in which the reasoning is sound but is based
upon a false initial statement
Example: All birds can fly; the penguin is a bird; therefore, penguins can fly.
False Analogy: an assumption that because two situations are similar, their
conclusions will be similar
Example: Universities, like businesses, have hierarchical structures; therefore
universities should be run like corporations.
False Dilemma or False Dichotomy or False Choice: a limited choice
between your opinion and one (usually extreme or opposite) other;
reducing an issue to a spurious either-or choice
Example: Anyone who opposes capital punishment must be pro-crime.
Some fairly consistent sources of logical fallacies are the opinion
pages of most newspapers, opinion columns in magazines, talk radio,
cable news programs, Sunday morning chat shows, and that
annoying blowhard who never shuts up in class. Also political
speeches often contain logical fallacies.
Logical Fallacies: The Exercise!
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Determine whether the following statements are logical.
If not, decide which logical fallacy (or fallacies) best applies.
Be careful, though: a statement can be based on faulty logic yet
still be true.
1. Star Wars is the greatest movie because no other movie is as good.
2. Of course we can all agree that women are generally more emotional than
men.
3. If you drink and drive, you increase your chances of getting into an accident.
4. Almost all of the people who called into the radio station said they dislike the
president. Apparently the president is extremely unpopular.
5. The only thing needed for a successful relationship with anyone is
communication.
6. The discovery of ancient craters that predate the disappearance of the
dinosaurs proves that asteroids or other extraterrestrial debris wiped out
the dinosaurs.
7. Every morning and evening, the B-12 bus is late. That bus is never on time.
8. Anyone who supports the right to bear arms obviously just likes killing
things.
9. If a man has $10.00 and gives $5.40 to his son and $3.60 to his daughter,
then the man has only $1.00 left.
10. I think the space program is a major mistake because, after all, whatever
goes up must come down.
11. No one would ever fight another war if people would just try to get along.
12. I do not care what your license says; I do not think that you are 21.
13. All men are mortal; Socrates is a man; therefore, Socrates is mortal.
14. I once worked for a government agency, and no one there did any work.
Most government workers are lazy.
15. Why would anyone believe a word she says? She dresses so badly!
16. All prisoners are criminals, of course, because otherwise they would not be
in jail.
17. There is no difference between political contributions and open bribery.
18. If we want some old-fashioned discipline among the young, we should bring
back the draft. Ending the draft has let young people grow soft.
19. The television station did one of those call-in polls and demonstrated that
the referendum will pass with overwhelming support.
20. Computers are smarter than humans; the Electron Prolinea 5100 is a
computer; therefore, the Electron Prolinea 5100 is smarter than humans.
21. Schools are like families, so teachers are parents while students are their
kids.
22. The Electron Prolinea 5100 is an ugly computer; your computer is quite
ugly, so it must be an Electron Prolinea 5100.
23. I will never be able to take Greg Granite seriously as a TV commentator so
long as he wears that ridiculous toupee.
24. I do not care what proof you have. I refuse to believe that aliens visit
earth.
25. You are either totally for me or totally against me.
26. Think about it: we never had an accident at the intersection until they
installed the new traffic light.
27. The candidate will never be elected. He is not popular enough. He needs
to appeal to more to his constituency, or not enough people will vote for
him.
28. All snow is cold precipitation; this precipitation is cold; therefore, this
precipitation is snow.
29. Since I got sick right after eating in that restaurant several times, I refuse
to eat there again.
30. As we all know, people always get what they deserve in the end.