Informal Fallacies
 Defective reasoning that makes weak arguments
appear stronger.
 Tools of advertisers, propagandists, charlatans, and
sincere yet self-deceived people who make claims
without the benefit of good evidence.
 Aristotle was the first thinker to begin to classify
various types of defective inferences that provide
psychologically persuasive (but not logically adequate)
reasons to believe a claim.
Fallacious Assumptions
 False Dilemma:
Presenting two
alternatives as the only
ones when others are
possible.
 Either you accept every
verse of Scripture as
God’s word or reject it all
as false human religious
speculation.
 If the glove does not fit, you must
acquit!
Sneaky Assumptions
 Complex question: Two
 Innuendo: Saying one
questions asked as one to
trap the unwary.
 How long have you had
the drinking problem?
 When will Fox and CNN
get out of bed with the
Bush administration?
 When will Obama stop
lying about his birth
certificate?
thing but suggesting
something more
negative.
 Yes, he’s telling the truth,
this time.
 She’s competent in many
ways.
 He’s pretty bright, for a
community college
instructor.
Circular Reasoning
 Begging the question: when the arguer assumes as a
premise the conclusion he or she is arguing for.
 Abortion is murder because it kills babies.
 No affirmative action policy can be fair or just because
you can’t fix one injustice by committing another.
 We have to have the death penalty to keep murderers
off our streets.
 We must reject Obamacare. Government programs are
never as effective as private enterprise.
Ambiguity
 Equivocation: Shifting
the meaning of an
ambiguous term.
 Knowledge is power.
Power corrupts.
Therefore, knowledge
corrupts.
We have the right to study
logic. We have a duty to
do right….
Ambiguous Phrasing: Amphibole
 Dog for sale. It eats
anything and is very fond
of children.
 If you don’t go to other
people’s funerals, they
won’t come to yours.
 He is trying to quit
smoking cold turkey.
 Tired of cleaning
yourself, let us do it for
you.
 False implication: When
an advertiser says
something true but
implies something that
isn’t true.
False Implication!
Fruity Pebbles
Captain Crunch Crunch Berries
Country Time Lemonade
The Navy, it’s not just a job,
its an adventure.
When you’re hungry, reach for a
Snickers.
You’ve come a long way, baby.
Tylenol, the official supplier of
pain relief products to the US
Olympic team.
Composition and Division
 Composition: Incorrectly
 Division: Incorrectly
inferring that what is true
of the parts is true of the
whole.
 We have the best athletes
in the league on our team,
so we have the best team.
 OxiClean is yours for just
four easy payments of
$19.95
inferring that what is true
of the whole is true of the
parts.
 USC has a great school of
business. Therefore, since
Jane went to USC, she must
be a great businesswoman.
 TRW is a high paying
company so Lester will
make a lot now that he
works for them.
Vagueness
 Abuse of vagueness: Using a vague expression for it’s
persuasive power as a substitute for evidence.
 Homosexual behavior is perverse because it isn’t
natural.
 Puffery: Intentional overstatement in advertising.
 Great Western Bank, we’ll always be there.
 Gillette, the best a man can get.
 Hype: Exaggeration: Amazing bargains! Incredible
deals! Biggest sale of the season!
More Advertising Fallacies
 Unspecified
 Weasel Words:
Comparison:
 When a product is
compared to an
unnamed competitor.
 Taster’s Choice Coffeesmoother taste.
Smoother than what?
 Less filling, lower in fat,
etc.
Advertisers use weasel
words to make vacuous
claims look substantive.
 Make your floor look like
new.
 Helps you look younger!
 Lasts up to eight hours.
Euphemism
 Using a term that sounds
 Loaded language- when
nicer than the reality it
refers to.
 Passed on
 Freedom fighters
 Friendly fire
 Terminate with prejudice
 We have to separate you.
the terms distort the
issue.
 Gun control fiasco
 War on drugs
 Abortion holocaust
 Illegal alien invasion
Extreme Quantifiers and
Intensifiers shut off debate.
 Everything she says is a
lie!
 PETA activists are
completely misguided.
 Obamacare is totally
flawed.
 I know that my redeemer
liveth!
Your resume claims you
are absolutely the greatest
Economics instructor in the
World (?)
Rhetorical Questions
 A question with only one
 Phantom Distinctions:
possible answer.
 Do you want some
government bureaucrat
deciding whether or not
you’re entitled to an
operation?
 Should scientists tinker
in God’s work?
Making a distinction to
suggest differences that
don’t really exist.
 No, you aren’t being fired
but your position has
been eliminated due to
downsizing.
 I’m not pro-abortion, I’m
pro-choice.
Red Herring
 When the arguer changes the subject to a different
issue which is psychologically, but not logically,
connected to the original issue.
 Some people say we need to do more about airline
safety. But more people are killed driving to the airport
than in plane crashes.
 How can you whine about dead seals when people are
being killed in Africa?
Straw Person
 Distorting another’s position (by making it appear
more radical, extreme, or simplistic than it really is)
and then attacking the distorted version of their view.
 PETA members think a human life is no more valuable
than the life of a cow, a rat, or even a cockroach.
 Liberal’s think poverty causes crime. What happened
to character and personal responsibility?
 Professor Dylan favors legalizing marijuana.
Apparently he wants to live in a society where everyone
sits around stoned out of their minds all day long.
Two Wrongs
 Shifts the blame by
 Common practice:
introducing an irrelevant
comparison:
 Henry Hyde argued that
Clinton should be
impeached. But he had
an adulterous affair that
destroyed a marriage.
Justifying some morally
suspect behavior by
claiming that others do it
too.
 There’s nothing wrong
with exaggerating your
business expenses for the
IRS. Everyone does it!
Ad Hominem
 Ad hominem (against
 Reverend Bud Green
the person) attacks the
arguer rather than the
substance of her
argument.
 Abusive ad hominem:
Attempts to discredit an
argument by assaulting
the character of the
arguer.
argues that hemp should
be legalized. But he is a
long-haired weirdo from
Venice Beach, so what
would you expect?
 Atheism starts in the
heart and spreads to the
head. Norman Geisler
Circumstantial Ad Hominem
 Attempting to discredit
an arguer’s position by
claiming that his view is
dictated by his
circumstances.
 Cindy argued against the
single payer health care
proposal. But she works
for Blue Cross, so of
course she is against it!
 Email adhominems
Dear Mari,
You stink and so does
your argument.
Guilt By Association
 Discrediting people,
Dear Tom,
No wonder your position stinks
because you are a stinking male!
Love, Mari
views, or arguments
based on someone’s
relationships with
others.
 We can ignore Rikki’s
anti-fur argument. She
belongs to PETA and they
are extremists.
More Ad Hominems
 Genetic Appeal:
 Poisoning the Well:
Evaluating an argument
or policy strictly in terms
of its origin.
 Christmas trees are of
the devil! They were first
used by Roman pagans.
 Government health care
plans are bad because
they originated in
socialist countries.
Attempting to create
prejudice against a
position before it has
been heard.
 Come on, Cardinal
Mahony! How can a
celibate male give an
argument on birth
control.
Provincialism and Tradition
 Provincialism: Appealing to group loyalty rather
than evidence to support a position.
 Support the B-2 Bomber! It means jobs for California.
 The Teachers Union advises a no vote on measure S.
 Appeal to Tradition: Claiming that a view is likely to
be true because it is affirmed by tradition.
 Marriage has always been an institution involving a man
and a woman. So we should not permit same sex marriages.
 Of course you will take my last name. Wives always do!
Novelty and Positioning
 Novelty: It is good
because it is new or
different.
 Vote Hayden, vote for
change!
 Positioning:
Positioning a product or
person with a better
known rival.
 7-Up, the uncola.
Damn, the novelty is already
wearing off.
Emotional Appeals
 Appeal to Anger: Arouse feelings of anger as a
substitute for evidence.
 If you want my gun you’ll have to pry it from my cold,
dead, hand!
 Appeal to Fear (or force)
 Listen, Galileo, drop this heliocentric nonsense or
Brother Vito will rotate your head around the sun!
 Hurry in! These unbelievably low prices won’t last!
FEAR!
Appeal to Pity
 Please officer! If I lose
If not either p nor
q imply not both
r and s, then q is not
quite true, I think.
Please, no truth tables on the exam.
I have an ulcer, I need less stress.
my license I’ll lose my
job. Who will pay for
Mama’s surgery?
 Stop animal testing!
Save Fluffy!
 Keep animal testing!
Save Granny!
Appeals to Authority
 Appealing to an authority who is either unqualified,
biased, mistaken, or lying; or when there is no
consensus of expert authority
 Invincible authority: Using an authority to override
all other evidence.
 The Bible says, “wives, obey your husbands.” So start
packing, we’re moving to Barstow.
 Forget what your mama taught you, Susan. Charlie
says we have to kill the pigs!
False Authority
Unidentified Authority
Irrelevant Authority
 When expert opinion is
 The authority cited must be
alluded to without explicit
identification of who the
expert is.
 Studies show that gun control
doesn’t work.
 Experts agree that legalizing
pot would be a disaster.
qualified on the topic in
question.
 Reverend John McArthur claims
that the theory of evolution is
not grounded in good science.
Apologist Hank Hanegraaff, the
Bible Answer Man, concurs with
this opinion. Hence, we can
conclude that evolution is a
flawed theory.
More False Authority Fallacies
 Testimonials: When a
celebrity or unknown
user of a product
endorses it’s value, their
testimony provides weak
support.
 Tiger Woods says drive a
Buick, chicks dig it!
 I lost 50 lbs in two days
with the lap band!
 Division of Expert
Opinion: When the
experts have not reached
a consensus, we cannot
appeal to one expert’s
view to resolve a dispute.
 We know alien abductions really
occur. Even Harvard
psychiatrist John Mack believes
alien abduction reports are
authentic.
Conflict of Interest
 When there is reason to
believe that the authority
cited has a vested
interest in the topic, his
or her testimony is
compromised by bias.
 The CEO of Shell Oil says
offshore drilling is
completely safe, so we
can approve their request
to drill.
 Bbb
 Trust me, I know!
Statistical Inference Fallacies
 Small Sample: Overestimating the statistical
significance of evidence derived from too few cases.
 In a published article, three gay men testified that their
homosexuality was a choice, not a decision forced on
them by their genes or upbringing. Thus, there is no
biological basis for male homosexuality.
 All three of my husbands had affairs so don’t deny the
fact that all men are cheaters.
 My husband died of brain cancer and he was a pot
smoker so marijuana smoking causes brain cancer.
Unrepresentative Sample
 Overestimating the
statistical significance of
a sample drawn from a
particular sample group
where a bias influences
responses.
 Of 50,000 residents of Salt Lake
City surveyed, 90% say they
oppose legal abortion. This
shows that Americans
overwhelmingly oppose abortion.
 Biased Methodology: A
study that uses loaded or
leading questions,
restricts range of
responses, etc.
 Do you favor Obama’s socialistic
health care reform that will
bankrupt our country, or do you
prefer to continue to allow
private enterprise to deliver the
best health care in the world?
Suppressed Evidence
 Deliberately ignoring
evidence that tends to
undermine one’s
position.
 I was the number one
salesman in the firm.
 See how much dirt was left
behind by your vacuum
when we vacuum the same
area with the Oreck 3000!
 We have less ships than we
had in 1916.
 Bad Base Line:
Overestimating the
significance of some
trend (in crime rates,
welfare rates,
unemployment rates,
etc.)
 Gambler’s fallacy: Thinking
past results of chance events
affect the probability of future
results.
 I’m due to win, baby!
Faulty Analogy
 An argument from analogy is weak when it ignores
relevant dissimilarities between the items compared or
uses similarities that are not relevant to the
conclusion.
 Sure guns kill, but so do baseball bats and no one wants to ban them!
 Guns kill people like spoons made Rosie O’Donnell fat and pencils
misspell words and cars make people drive drunk.
 "This bill [to ban the carcinogen chlordane] reminds me of legislation
that ought to be introduced to outlaw automobiles" on the grounds
that cars kill people, said Rep. Tom DeLay, R-Texas,
Ad Ignorantiam
 An argument from ignorance misplaces the burden of
proof by claiming either that because a certain claim
has not been proven false, it is probably true, or that
because a claim has not been proven true, it is
probably false.
 No one can prove that angels don’t walk among us!
 Invincible Ignorance: To refuse to accept the burden
of proof by denying all evidence that contradicts a
position.
 You can keep your fossils and biology books, Genesis is God’s word and
it don’t say I come from no monkey!
Causal Fallacies
 Confusing correlation
with causation.
 83% of criminals drink
alcohol before committing
crimes. So Alcohol use
causes crime.
 Post hoc ergo propter
hoc. Mistaking temporal
succession for causal
connection.
 Prayer works! I said four
“Hail Mary’s” before the
game and the Chargers
won!
 Common Cause:
Inferring a causal
connection when two
items are both produced by
an underlying cause.
 75% of Prozac users have
contemplated suicide. That stuff
is dangerous!
Causal Oversimplification
 Mistaking a contributing
 False Inference to Best
cause as the primary
cause.
 We can resolve the
budget crisis in
California if we crack
down on illegal
immigration and stop
giving benefits to people
who are here illegally!
Explanation:
Maintaining an
implausible hypothesis
simply because you
haven’t thought of a
better explanation.
 I must have been a Egyptian
princess in a past life because I
uttered some Egyptian words
during hypnotherapy.
Questionable causal
assumptions
 Disease and natural
 Demons are influencing
disasters are divine
punishments for human
sin.
 Comic books, or video
games, or certain types
of music produce
juvenile delinquency
 A close brush with death
means God saved you
from harm.
events.
 Personality is affected by
date of birth.
 George Bush was
responsible for 9/11
 Genetically modified
food is harmful.
 God wants one person to
kill another.
Slippery Slope
 An unwarranted
prediction of disastrous
results from adopting
some policy.
 If we allow terminally ill
patients to take their own
lives, respect for the
sanctity of life will
diminish. Soon the elderly
and the disabled will be
killed against their will.