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Informal Fallacies I

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Mark Thorsby

on 1 June 2011

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Transcript of Informal Fallacies I

Fallacy - from L. "fallacia", meaning deceptive - A deceptive or false satetment.
Fallacy: from L. "fallacia" meaning deceptive - a deceptive statement or argument
Fallacy - from L. "fallacia" or decpetion - a deceptive argument or statement
Two Types of Fallacy Possible:
Formal Fallacies:
Affirming the Consequent

Denying the Antecedant

Informal Fallacies
Informal Fallacies Concern the
of an Argument
Here is an Example:

The Brooklyn Bridge is made of atoms
Atoms are invisible
Therefore, the Brooklyn Bridge is invisible
Here is the Form:

Valid Form: Hypothetical Syllogism
Unsound Argument:

To detct the fallacy you need to know something
about the conceptual content - namley, that bridges
are large visible objects.
Fallacies that involve mistakes in reasoning
are refred to, in Latin, as
non sequiturs
(it does not follow)
A) Fallacies of Relavance
Fallacies of irrelevance share the common characteristic that the arguments in which
they occur have presmises that are logically irrelevant to a conclusion,
but may appear psychologically relevant.
B) Fallacies of Weak Induction
Fallacies of Weak Induction occur when the link
between the premises and the conclusion
is too weak.
C) Fallacies of Presumption, Ambiguity, & Weak Induction
These Fallacies occur when
(1) the premises presume the conclusion
(2) when an argument uses terms in an ambiguous sense
(3) when the grammar of an argument hides a fallacious relation
D) Fallacies of Ordinary Language
The majority of informal fallacies occur in ordinary language,
and are very difficult to detect and often employ unstated
premises, conclusions... ie. everything else.
To identify fallacies of relevance, one must be able to distinguish genuine evidence from various forms of emotional appeal.
The fallacy of appeal to force occurs whenever an arguer poses a conclusion to another person and tells that person either implicitly or explicitly that some harm will come to him or her if he or she does not accept the conclusion.
Appeal to Force
(argumentum ad Baculum:
Appeal to the ‘stick’)
“If you don’t give me a raise within the next month, you may just show up to work and discover that the building has burned down.”
Appeal to Pity
(Argumentum ad misericordiam)
The appeal to pity fallacy occurs when an arguer attempts to support a conclusion by merely evoking pity from the reader or listener. The pity can be directed to either the listener or a third party
“Your honor, I admit that I declared thirteen children as dependents on my tax return, even though I only have two. But if you find me guilty of tax evasion, my reputation will be ruined. I’ll probably lose my job, my wife will not be able to have the operation she desperately needs, and my kids will starve. Surely I can’t be guilty.”
Appeal To The People
(Argumentum ad Populum)
The fallacy of appeal to the people operates by using such basic social desires as love, esteem, admiration, value, recognition, etc. to get a reader or listener to accept a conclusion.
3 types of Appeal to the People
1) The Bandwagon Argument
ex) “Of course you want to buy Crest toothpaste; 90% of America brushes with Crest.”

2) Appeal to Vanity
ex) “The most beautiful women choose Loreal.”

3) Appeal to Snobbery
ex) “A Rolls-Royce is not for everyone. If you qualify as one of the select few, this distinguished classic may be seen and driven at British Motor Cars, Ltd. (By appointment, please)”
Against the Person
(Argumentum ad hominem)
This fallacy always involves two arguers. One of them advances (either directly or implicitly) a certain argument, and the other responds by directing his or her attention not to the first person’s argument but to the first person herself.
3 types of Ad Hominem
1) Abusive
“Before, he dies, poet Allen Ginsberg argued in favor of legalizing pornography. But Ginsberg’s arguments are nothing but trash. Ginseberg was a pot smoking homosexual and a thoroughgoing advocate of drug culture.”

2) Circumstantial
“Of course President Bush wants to invade Iraq. Iraq has the world’s second largest oil supply and he is from an oil tycoon family.”

3) Tu Quoque (“you too”)
“Your argument that I should stop stealing candy from the corner store is no good. You told me yourself just a week ago that you, too, stole candy when you were a kid.”
Quick Write Exercise
Fallacy of Accident
The Fallacy of Accident is committed when a general rule is applied to a specific case it w
as not intended to cover. Typically, the general rule is cited in the premises and then wrongly applied to a specific case mentioned in the conclusion.
Accident Example
“Freedom of Speech is a constitutionally guaranteed right. Therefore, John Smith should not be arrested for yelling ‘fire’ in a crowded theatre.”
“Property should be returned to its rightful owner. That drunken sailor who is starting a fight with his opponents at the pool table lent you his .45 -caliber pistol, and now he wants it back. Therefore, you should return it to him now.”
Straw Man
The Straw Man Fallacy is committed when an arguer distorts an opponent’s argument for the purpose of more easily attacking it, demolishing the distorted argument, and then concludes that the opponent’s real argument has been demolished.
Straw Man Example
“Mr. Goldberg has argued against prayer in the public schools. Obviously Mr. Goldberg advocates atheism. But atheism is what they used to have in Russia. Atheism leads to the suppression of all religions and the replacement of God by an omnipotent state. Is that what we want for this country? I hardly think so. Clearly Mr. Golberg’s argument is nonsense.”
Missing the Point
(Ignoratio Elenchi)
The Missing the Point Fallacy illustrates a special form of irrelevance. This fallacy occurs when the premises of an argument support one particular conclusion, but then a different conclusion, often vaguely related to the correct conclusion, is drawn.
If you suspect this type of fallacy, you should be able to identify the correct conclusion which follows logically.
Missing the Point Example
“Crimes of theft and robbery have been increasing at an alarming rate lately. The conclusion is obvious: we must reinstate the death penalty immediately”
“Abuse of the welfare system is rampant nowadays. Our only alternative is to abolish the system altogether.”
Red Herring
(Ignoratio elenchi)
(Being led astray by a False Scent)
The red herring fallacy is committed when the arguer diverts the attention of the reader or listener by changing the subject to a different but sometimes subtly related one. He or she then finishes by drawing a conclusion about a different issue by merely presuming that some conclusion has been established.
Red Herring Example
“Environmentalists are continually harping about the dangers of nuclear power. Unfortunately, electricity is dangerous no matter where it comes from. Every year hundreds of people are electrocuted by accident. Since most of these accidents are caused by carelessness, they could be avoided if people would just exercise greater caution.”
Appeal to Unqualified Authority
(Argumentum ad Verecundiam)
Appeal to Ignorance
(Argumentum ad Ignorantiam)
Hasty Generalization
(Converse Accident)
False Cause
Slippery Slope
Weak Analogy
David Duke, former Grand Wizard of the Klu Klux Klan, has stated,
"Jews are not good Americans. They have no understanding of what
America is." On the basis of Duke's authority, we must conclude that
the Jews in this country are un-American.
No on has been able to prove God exists, therefore God does not exist.
No one has disproven God's existence, therefore he must exist.
Ten Arab Muslims hijacked planes and crashed them into
the Worl Trade Center in New York City on Sept. 11, 2001.
It is clear that Muslims hate America and resort to violence.
During the past two months, every time that the cheerleaders have worn blue ribbons in their hair, the team has been defeated. Therefore, to prevent defeats in the future, the cheerleaders should get rid of those blue ribbons.
Step 1
"Attempts to outlaw pornography threaten basic civil rights and should be
summarily abandoned. If pornography is outlawed, censorship of news-
papers is only a short step away. After that there will be censorship of textbooks,
political speeches, and the content of lectures delivered by university
professors. Complete mind comtrol by the central government will be the
inevitable result."
The fallacy of weak analogy occurs when an analogy
is too weak to support a conclusion.
The Pocket Watch Argument for God's Existence
The Structure of the Argument
Entity A
Entity B
Full transcript