What’s a logical fallacy and why
should you care?
 It’s poor logic partly consisting of
overgeneralizations and assumptions.
 The presence of logical fallacies may weaken
a writing project. When you’re developing an
argument, your points should follow in logical
order and make proper conclusions.
 When you’re refuting a counterargument
(procatalepsis), it’s useful to point out logical
fallacies as weak points in your opponent’s
Fallacies can refer to…
a kind of error in an argument,
a kind of error in reasoning (including
arguments, definitions, explanations,
and so forth),
a false belief, or
the cause of any of the previous errors,
including what are normally referred to
as "rhetorical techniques".
Why learn logical fallacies?
 To point them out when an opponent uses one or offer
reasoning if you use them.
 Make you look smart.
 Impress judges.
 To remove an argument from the table, not just
weaken it.
 To know when you are using them and prepare for
your opponent’s argument, rather than being taken off
How do you point them out?
 State the name of fallacy in Latin and English,
making sure to use the phrase “logical fallacy.”
 Explain what the fallacy means and why it is
wrong, but do it without sounding pedantic ~
smarter than everyone else.
 Give a really obvious example of why the
fallacy is incorrect, preferably an unfavorable
analogy for your opponent’s case.
 Point out why the fallacy matters.
Common Fallacies
Argumentun Ad Antiquitatem
 The argument to antiquity or tradition.
 Argument that a policy, behavior or practice is right or
acceptable because “its always been done that way”.
 Ex: “Every great civilization in history has provided
states subsidies for art and culture.”
 Try to avoid it; if you do use it, give a reason why it
should be considered.
Argumentum Ad Hominem
 Argument directed at the person.
 Attacking the character or motives of a person
who has stated an idea rather than the idea
itself; can also be an attack on the source of
 Ex: Richard Nixon was liar and a cheat.
 Also occurs when the person has something to
gain from the policy.
 Ex: Bill Gates talking against antitrust legislation
Argumentum Ad Ignorantiam
 Argument to ignorance.
 Assuming something is true simply because it
hasn’t been proven false.
 Example: Global warming is true because nobody
has demonstrated conclusively it is not.
 Whomever has “burden of proof” (usually
affirmative) has to be careful in using this fallacy.
 Ex: Prosecution who says that no alibi means
guilty vs. defense saying prosecution didn’t prove
case so defendant is not guilty.
Argument Ad Logicam
 Argument to logic.
 Assuming that something is false simply because
proof that someone has offered for it is invalid.
 AKA Straw Man Argument.
 Burden of proof determines whether it is fallacy or
 Ex: If affirmative team fails to provide sufficient
support for its case, the burden of proof dictates
they lose the debate even if there exists other
arguments not presented that could have supported
the case.
Argumentum Ad Misericordian
 Appeal to pity.
 Ex: Think of all the poor, starving people in
Ethiopia. How can we not help them?
 This doesn’t mean you can’t argue for
something like aid to Ethiopia, but it does
mean that you can’t just use emotional pleas.
Argumentum Ad Nauseam
 Argument to the point of disgust or repetition.
 Trying to prove something by saying it again
and again.
 Stating a main point over and over again
instead of real arguments.
 Make sure you SUPPORT your main points.
Argumentum Ad Numerum
Argument to numbers.
Attempt to prove something by showing
how many people think that it’s true.
Ex: 70% of all Americans support
restrictions on access to abortions.
Argumentum Ad Populum
Appeal to people or to popularity.
Trying to prove something by showing
that the public agrees with you.
Narrowly designates an appeal to the
opinions of people in the audience.
Ex: You should turn to Channel 8. It's the
most watched channel this year.
Argumentum Ad Verecundiam
 Argument to authority.
 Someone tries to demonstrate the truth of a
proposition by citing some person who agrees,
even though that person may have no
expertise in the given area.
 Ex: Quoting Einstein on politics.
Circulus In Demonstrando
Circular argument.
Someone uses what they are trying to
prove as part of the proof of that thing.
Always illegitimate but hard to spot.
Ex: A couch is a sofa. A sofa is a
davenport. A davenport is a couch.
Complex Question
 Question that implicitly assumes something to
be true by its construction.
 Ex: The majority of black Americans live in
poverty, but do you really think that self-help
within the black community is sufficient to
address their problems?
 Only a fallacy when used for something that
hasn’t been proven.
Cum Hoc Ergo Propter Hoc
 With this, therefore because of this.
 Usually called cum hoc.
 Mistaking correlation for causation - because
two things occur simultaneously, one must be
a cause of the other.
 Ex: Gypsies live near our low-yield cornfields.
Therefore, gypsies are causing the low yield.
Dicto Simpliciter
 Sweeping generalization.
 Making a sweeping statement and expecting it
to be true of every specific case; stereotyping.
 Example: Women on average are not as
strong as men and less able to carry a gun;
therefore, women can’t pull their weight in a
military unit.
Either – Or / False Dilemma
Asserts that a complex situation can have
only two possible outcomes and that one of
the options is necessary or preferable.
 Ex: Either go to college or forget about making
False Analogy
 An analogy points out similarities in things that
are otherwise different.
 A false analogy claims comparison when
differences outweigh similarities.
 Essentially, it’s comparing apples and oranges!
Nature, appeal to
Assuming that whatever is natural or
consistent with nature is good or that
whatever conflicts with nature is bad.
Fairly rare, but usually seen in
environmentalist argument.
Non Sequitur
 It does not follow.
 Stating as a conclusion, something that does
not strictly follow from the premises.
 Ex: Racism is wrong, therefore, we need
affirmative action.
Petitio Principii
 Begging the question.
 Assuming, when trying to prove something, what it is
that your are trying to prove.
 Very similar to circular argument.
 Occurs when a question has been asked before in the
discussion, then a conclusion is reached on a related
matter without the question having been answered.
 Ex: Person 1: He is mad right now.
Person 2: How do you know?
Person 1: Well, because he is really angry.
Post Hoc Ergo Propter Hoc
 After this, therefore because of this.
 Assuming that A caused B simply because A
happened prior to B.
 Ex: Most rapists read pornography when they
were teenagers; obviously, pornography
causes violence toward women.
 Similar to cum hoc ergo prompter hoc.
Red Herring
 Introducing irrelevant facts or arguments to
distract from the question at hand.
 Ex: The opposition claims that welfare
dependency leads to higher crime rates; but,
how are poor people supposed to keep a roof
over their heads without our help?
 It is not fallacious to argue that benefits of one
kind may justify incurring costs of another
Reductio Ad Absurdum
Useful in creating a comic effect.
Assumes a claim for the sake of
argument, derives an absurd or
ridiculous outcome, and then concludes
that the original assumption must have
been wrong as it led to an absurd result.
Slippery Slope
 Not always a fallacy.
 Argument that says adopting one policy or
taking one action will lead to a series of other
policies or actions also being taken without
showing a causal connection between the
advocated policy and the consequent policies.
 Ex: If we legalize marijuana, the next thing
you know we’ll legalize heroin, LSD and crack
Tu Quoque
 You too.
 Defending an error in one’s reasoning by
pointing out that one’s opponent has made the
same error.
 Ex: They accuse us of making unjustified
assertions, but they asserted a lot of things,
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