Chapter 4: Informal Fallacies
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In This Chapter
Fallacies of Relevance
Fallacies of Unwarranted Assumption
Fallacies of Ambiguity or Diversion
Recognizing Fallacies in Ordinary Language
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Fallacy: A defect in an argument that consists in
something more than merely false premises. Both
deductive and inductive arguments may contain
fallacies, and, if they do, they are either unsound
or uncogent, depending on the kind of argument.
Also, if an argument is either unsound or
uncogent, then it has one or more false premises
or contains a fallacy or both.
Two kinds of fallacies: formal fallacies and informal
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Informal Fallacies
• Formal fallacy: A logical error in a deductive
argument that occurs in the form or structure of an
All beagles are dogs.
All poodles are dogs.
All B are D.
All P are D.
All beagles are poodles.
All B are P.
Any substitutions of
this exact form will
also be INVALID
• Informal fallacy: A mistake in reasoning that occurs
in ordinary language, including mistakes due to
relevance, unwarranted assumption, and ambiguity
or diversion.
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• Informal fallacies cannot be detected by form, but require an
analysis of content, regardless of whether the argument is
inductive or deductive.
All factories are plants
All plants have chlorophyll
All factories have chlorophyll
This appears to have the form:
All A are B
All B are C
All A are C
Which is clearly valid.
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But, given that the word “plant” is used in two different
ways, the form is actually:
All A are B
All C are D
All A are D
Notice, then, the argument contains an informal and a
formal fallacy.
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Fallacies of Relevance
Fallacies that occur
whenever irrelevant
premises are offered in
support of a conclusion.
Irrelevant premises often
rely on psychological or
emotional appeal for
their persuasive force.
1. Argument Against the
2. Tu Quoque
3. Appeal to the People
4. Appeal to Pity
5. Appeal to Force
6. Appeal to Ignorance
7. Missing the Point
8. Appeal to an Unqualified
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Argument Against the Person
Argumentum ad Hominem — “to the person”
When a claim is rejected based on alleged character flaws,
negative stereotype, or life circumstances of the person
making the claim.
Senator Hilltop thinks my
administration’s tax proposals are bad
for the country. His political party lost
the last election. Members of the
losing party are always jealous of the
winning party.
The premises attack
Senator Hilltop's party
affiliation and
stereotype the senator
and his party.
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Tu Quoque
Tu Quoque —“you, too”
A type of ad hominem fallacy distinguished by the attempt of one
person to avoid the issue at hand by claiming the other person is a
You have been lecturing me about
not joining a gang. But Dad, you
were a gang member, and you
never went to jail. So, I'll make my
own decision about joining a gang.
This tu quoque attack is aimed at
the dad, not at dad's arguments.
The premises are used to imply
that “Dad, you are a hypocrite,”
which is then used to reject
Dad’s arguments: I can disregard
your lectures.
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Appeal to the People
Argumentum ad Populum
The avoidance of objective evidence in favor of an emotional
response, defeating a rational investigation of truth.
Public schoolteachers are demanding
a pay raise and are threatening to
strike. A prolonged strike will
jeopardize our children’s future and
result in an unbalanced budget,
leading to raised taxes. So are you for
or against a pay raise for public
school teachers?
Terms like demanding,
threatening, prolonged
strike, and jeopardize
evoke a sense of dire
consequences and
provoke anger in
taxpayers and voters.
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Appeal to Pity
Argumentum ad Misericordiam — “from pity or guilt”
An emotional plea that relies solely on a sense of pity for
Your honor, before you sentence my
client for the murder of his parents,
I ask you to consider his situation.
He is an orphan. Perhaps you can
give him the lightest punishment
The premises simply
ask the judge to pity
the defendant because
he is a self-caused
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Appeal to Force
Argumentum ad Baculum — “appeal to the stick”
A threat of harmful consequences (physical and otherwise)
used to force acceptance of a course of action that would
otherwise be unacceptable.
If the workers of this company do
not agree to a 25% cut in salary,
then the company may have to
shut its doors. Therefore, the
workers of this company must
agree to a 25% cut in salary.
The premise is an obvious
threat without providing
objective evidence for the
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Appeal to Ignorance
Argumentum ad Ignorantiam — “arguing from ignorance”
An argument built on a position of ignorance claiming either:
a statement must be true because it has not been proven to be false or
a statement must be false because it has not been proven to be true.
There is no life anywhere
else in the universe. We
have never received
signals from any part of
The conclusion is based on
the lack of signals from outer
space, while our failure to
detect signals may signify our
ignorance of better methods
for detecting life.
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Missing the Point
Ignoratio Elenchi — “irrelevant proof”
When premises that seem to lead logically to one
conclusion are used instead to support an unexpected
If we buy a second car, the
insurance will only be an
additional $400 a year. Let’s go
get one before the insurance
company changes the rate.
The gap between the
premises and
conclusion is so great
that the conclusion
becomes, in a sense,
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Appeal to Unqualified Authority
Argumentum ad Verecundiam — “appeal to reverence or respect”
Relies on the opinions of people who have no expertise,
training, or knowledge relevant to the issue at hand.
I'm Nick Panning, quarterback of the
Los Angeles Seals. I've been eating
Oaties for breakfast since I was a kid.
Oaties provides nutrition and
vitamins and helps build strong
bones. Oaties tastes great. You
should get some for your kids today.
Merely being
famous does not
qualify someone to
pronounce the
merits of a product.
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