Logical Fallacies
What are logical fallacies?
 Mistakes in our reasoning
 Claims, warrants, or pieces of evidence are invalid, insufficient,
or disconnected
 Seriously affect our ability to argue effectively
 Sometimes we think that our faulty argument is sound
 Sometimes we think a flawed argument will win us the battle
 Sometimes these are difficult to spot because they
are disguised by the skillful use of words or images.
Fallacies
 Ad Hominem—Against the Man

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Circumventing the issue by attacking a person’s character
Used to divert an audience’s attention from the issue at hand
 Argument to the People

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Seeking assent by stirring up powerful emotions (like fear or
prejudice) instead of building a logical case
Used to divert an audience’s attention from the issue at hand
 Complex Question

A question that actually contains two questions that need to be
addressed separately OR a question where all answers support an
assumption
“Where did you go after you stole the car?”
 Two separate issues

Fallacies
 Begging the Question
 Circular Reasoning
Drawing conclusions from assumptions that have not been proven
 CLAIM: You can’t give me a C in this course…
 REASON: …because I am an A student.
 WARRANT: An A student is someone who can’t receive Cs.

 Either/Or Fallacy
 Contrasting your own choice only with one that is completely
undesirable; Overlooking other options
Fallacies
 Equivocation
 Using a word with two or more definitions, usually in order to
confuse or deceive


Macbeth has nothing to worry about “till Birnam wood / Do come
to Dunsinane” –how can a forest move?
An argument gives an honest appearance
 Half-Truth
 Building your argument on verifiable facts but deliberately
failing to give your audience the full story.
Omitting key facts and details
 Can be just as harmful to your credibility as giving blatant
falsehoods

Fallacies
 Hasty/Faulty Generalization

Inference drawn from insufficient evidence


Because my Honda broke down, then all Hondas must be junk.
Sweeping claims of little merit
Women are bad drivers.
 Men never ask for directions.
 English teachers are nitpicky.

 Faulty Causality

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Error in causal reasoning—assumes that because one action follows
another, the first causes the second
LATIN! Post hoc, ergo propter hoc “after this, therefore because of
this”

The abnormally warm weather led to the increased number in
summer casualties
Fallacies
 Faulty Analogy
 Assuming that since two things are alike in one aspect, they
must be alike in others

Comparing the war in Iraq to World War II
 Non-Sequitur
 Literally means “it does not follow.”
 A conclusion or statement that does not arise logically from the
premises of a given argument

You don’t love me or you’d buy me that bicycle!
Fallacies
 Red Herring
 Introducing something irrelevant/tangential to change or shift
the topic

Why should we worry about the amount of violence on television
when thousands of people are killed in automobile accidents every
year?
 Straw Man
 Strengthening your own view by distorting/oversimplifying the
opposing view
 Attacking an argument that isn’t really there.

People arguing against evolution might insist that the adherents
hold that evolution is all chance and random
 This is addressing an argument that hasn’t been made
Fallacies
 Bandwagon
 Assumes that because something is popular, it is desirable,
good, or correct

The President must be correct in his approach to foreign policy;
after all, the polls show that 60 percent of the people support him.
 Slippery Slope

Assumes that taking a first step will lead to subsequent steps that
cannot be prevented

If we allow the government to restrict the sale of semi-automatic
weapons, before we know it, there will be a ban on the ownership of
handguns and even hunting rifles. And once our constitutional right to
bear arms has been compromised, the right of free speech will be the next
to go.