Logical
Fallacies
What is a logical fallacy?
An error in reasoning that undermines or invalidates
an argument.
Logical fallacies are fairly common but must be avoided
in order to produce strong, reliable arguments.
Common
Fallacies
There are many fallacies, but let’s just look at a few.
LOGOS
Post Hoc
● Other names: Faulty Causality
● Definition: Confusing correlation with causation
● Formula: because B comes after A, A caused B
● Example: After the teacher starting giving more tests,
cheating in class became more common. Therefore,
having more tests causes more cheating.
LOGOS
Slippery Slope
● Other names: The “Camel’s Nose” Fallacy
● Definition: Assuming one action will lead to a set chain of
consequences
● Formula: If A, then B, and if B, then C
● Example: If he does not study for this test, he will fail it, and
then he will fail the class. If he fails the class, he will never
get into a good college or get a good job.
LOGOS
Begging the Question
● Other names: “Circular Reasoning” is one way to do this
● Definition: asks the audience to simply accept the
conclusion without providing real evidence for the premise
● Formula: A is B because A.
● Example: Freedom of speech is important because people
should be able to speak freely.
LOGOS
Hasty Generalization
● Other names: Dicto Simpliciter or “Jumping to Conclusions”
● Definition: Drawing a conclusion based on insufficient or
biased evidence
● Formula: Based on A, B, and C, D-Z must also be the same.
● Example: I heard that three other people made an A on their
project. Therefore, most people in the class must have made
an A on the project.
PATHOS
Appeal to Fear
● Other names: Scare Tactics
● Definition: Using fear as the primary reason a claim should
be accepted as true
● Formula: A is a something to fear; therefore B should be
implemented to prevent A.
● Example: If your candidate is elected, this country will go to
pieces. Therefore, you should elect my candidate instead!
LOGOS
Argument from Ignorance
● Other names: Appeal to a Lack of Evidence
● Definition: Saying that since you cannot disprove something,
it must be true.
● Formula: A must be true because no one can prove it is not.
● Example: Ghosts must be real because no one has been able
to prove that they are not!
LOGOS
Red Herring
● Other names: Ignorantio Elenchi
● Definition: Distracting from the claim or counterclaims by
bringing up a side issue
● Formula: A might be true, but B is also an issue.
● Example: Yes, I probably should have done my homework,
but there are so many other students out there breaking all
kinds of school rules!
LOGOS
Straw Man
● Other names: A kind of Red Herring argument
● Definition: Oversimplifying an opponent's viewpoint and then
knocking down that hollow argument
● Formula: My opposition’s position A is extreme or absurd and
must be untrue.
Example: Speaker 1: "The state should increase funding to unemployed single
mothers because they need money to provide medical care for their children."
Speaker 2: "My opponent believes that lazy, jobless parasites should get a free
ride from the tax money of hard-working honest citizens. He’s wrong because…”
LOGOS
PATHOS
Appeal to Ridicule
● Other names: Appeal to Mockery, Horse Laugh
● Definition: Similar to Straw Man, an opposing view is
presented as absurd or ridiculous
● Formula: Person 1 claims that A is true. Person 2 makes A
look ridiculous, by misrepresenting A. Therefore, A is false.
● Example: Sure, you can join that club...if you want to look like
an idiot!
LOGOS
False Dichotomy
● Other names: False Dilemma, Either/Or Fallacy
● Definition: Oversimplifying an argument by saying there are
only two options
● Formula: We can either do A, or B will happen.
● Example: You can either go to the party or never have a
chance at a social life.
ETHOS
Ad Hominem
● Other names: Poisoning the Well, Personal Attack
● Definition: Attacking the person who makes an argument
instead of the argument itself
● Formula: Because my opponent is -negative trait-, his
claim must be untrue.
● Example: Jason can’t be the team captain because he is
unattractive and a little overweight.
ETHOS
Argument from Authority
● Other names: Appeal to Improper Authority
● Definition: Assuming an argument is true because of who is
saying it when their status suggests no expertise
● Formula: Because -authority- says so, A must be true.
● Example: I’m going to vote for that candidate because my
favorite band said that people should!
LOGOS
PATHOS
Ad Populum
● Other names: Bandwagon is a common type
● Definition: Assuming people should do/believe something in
order to be accepted by the majority
● Formula: Because so many people believe A, A must be
true
● Example: 70% of people say they would vote for this
candidate, so you should vote for her too!
Testing for
Logical Fallacies
Some guidelines from UNC Chapel Hill’s Writing Center
When looking...
● Pretend you disagree with the conclusion you see.
○ What parts of the argument would now seem fishy to you?
● List the main points; under each one, list the evidence for it.
○ You realize there is no good evidence for a particular claim, or it may
help you look more critically at the evidence used.
● Be aware that broad claims need more proof than narrow ones.
○ Claims that use sweeping words like all, none, every, always, never,
etc. require a lot more proof than less-sweeping claims
● Double check characterizations of others, especially opponents, to
be sure they are accurate and fair.