INFORMAL INFORMAL FALLACIESFALLACIES
http://www.fallacyfiles.org/glossary.html
Quiz: *Your NAME*Give a description of ONE informal fallacy. (From the Arthur article, or from FallacyFiles.org
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Response Essay due March 12Download from Files Assignments:Response Essay InstructionsTips for writing essaysRead some sample essays.
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6 ways to critique an argument
1. Check to see if the reasoning is VALID (E.g. does the conclusion follow from the premises?).
2. Check to see if it is SOUND (e.g. are the premises true?).
3. Check for STRONG or WEAK sample sizes (if it is an inductive argument).
4. Check for unstated ASSUMPTIONS in the argument.
5. Check for unwanted or absurd CONSEQUENCES of an argument (i.e. assume the argument is sound).
6. Check for informal FALLACIES.
Slippery slope
• "If we lower the drinking age from 21 to 18, then what next? 16 year olds being allowed to drink? 14 year olds?"
• "If we allow the French to influence us, we'll soon be eating nothing but snails and garlic."
--Slippery slope:Supposing that a single step
in a particular direction must lead to the extreme position.
Slippery slope• To critique a slippery slope:• Write the Author’s ARGUMENT, with premises and
conclusions. • One of the premises will contain a slippery slope,
with STEPS of the slope• List step A, B, C. . .Z, where the author thinks step A
will NECESSARILY lead to step Z• Then give your own argument to show that steps A,
B, C do NOT lead to step Z.
--Slippery slope:Supposing that a single step in a particular
direction must lead to the extreme position.
Slippery slopeI.e. “Legalizing marijuana will lead to economic
collapse.• The ARGUMENT:• P1. If we legalize marijuana, then our economy will
collapse • P2. We don’t want our economy to collapse.• C. We should not legalize marijuana. • THE STEPS:• A. If we legalize mary J, then people will become
slothful,• B. If people are slothful, then they won’t work• Z. If people don’t work, then our economy will
collapse. • Then, you will argue why step b doesn’t necessarily
follow from step A. • Direct cable commercial: http://www.youtube.com/watch?v=c-zG5U0v3gU
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Begging the question• "Justice requires higher wages because it is right
that people should earn more." • This amounts to: "justice requires higher wages
because justice requires higher wages.”
– God exists!– How do you know?– The Bible says so.– How do you know that what the Bible says is true?– Because the Bible is the word of God!
--Begging the question: (petitio principii)The argument uses the conclusion that it seeks to establish. It assumes the conclusion in its premises.
Circular definition:
• "Since I'm not lying, it follows that I'm telling the truth.“– Bill: “I enjoy only good books.”– Tom: “How do you know when they’re good?”– Bill: “If they’re not good, I don’t enjoy them.”
-- Circular definition:The definition includes the term being defined
as a part of the definition; Using the concluding claim as evidence to support the conclusion.
• Break into groups of 3-4. • Read the examples, definition,
explanation, etc. of the fallacy.• Summarize the fallacy briefly in your
own words.• Give your own examples of the fallacy.• Argue why the example is a fallacy,
using a counterexample or analogy. • Choose a spokesperson to tell the class
about your fallacy.
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Appeal to popularity
• Everyone believes X, so X must be true.
• Thinking conclusion is true because it is a popular belief.
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Post hoc
• "After Ketchup was considered a serving of vegetables in school meals, math scores dropped nation-wide. Therefore, ketchup causes math scores to drop."
-- Post hoc ergo propter hoc: (Post hoc for short. Latin: "after this, therefore because of this.") Because one thing follows another,
it is held to cause the other. FORM:Event C happened immediately prior to event E. Therefore, C caused E.
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Cum hoc• "In K-12 children, neater handwriting causes larger feet.“
• “The number of cases of drowning increases as the sale of ice cream increases. So eating ice cream must cause drowning.”
• Cheerios: studies show that people who eat whole grains tend to have healthier body weight.
-- Cum hoc ergo propter hoc: Assumes events which occur together are causally connected,and there is no room for coincidence or for other causal factors. FORM: Events C and E both happened at the same time. Therefore, C caused E.
Ad Hominem
• "How can you condone usury? You're a Christian, and Christ drove the money-lenders from the temple."
• ”As an opera-lover, you will be the first to agree that we need more subsidy for the arts."
-- Argumentum ad Hominem:Attacking the arguer rather than the argument itself. It also includes invoking the proponents position.ALSO: TU QUOQUE
Straw man
• “We should liberalize the laws on marijuana.”
• “No. Any Society with unrestricted access to drugs loses its work ethic and goes only for immediate gratification.”
-- Straw Man:A deliberate over-statement of an opponent's position. Stating a position that no one holds.
Argument from ignorance
• "We don't know what caused the door to slam, therefore it was a ghost.“
• We don’t have proof that God exists, therefore he does not exist.
-- Argument from ignorance:Using the lack of knowledge
of any alternatives to justify the truth of a claim.
bifurcation
• "If you are not with us, you are against us." -W
--Bifurcation:Presenting only two alternatives
where others exist; black and white thinking.ALSO: FALSE DILEMMA
Anecdotal evidence
• Anecdotes and stories • These are events that happen to someone, or
that are told to them, with no attempt at any scientific analysis. Some are simply stories, events that did not really happen or that have been significantly altered (for example urban legends). They are useful for adding interest, and in illustrating points, but they should not be used to make generalizations.
• "This is third day in a row that we've had a record high temperature. Global warming must be real." 19
Tu quoque
• "You can't tell me smoking is bad when you've been smoking for thirty years."
-- Tu Quoque: ("you also")Undermining a case by claiming
that its proponent is himself guilty of what he talks of.
Genetic fallacy
• "Since you based your theory of Bigfoot on stories from The National Enquirer, the theory must be false.”
• “The war on drugs started from strict Puritanical heritage. So we don’t have to encourage drug control.”
-- The genetic fallacy: (p. 89)Attacking the source of the argument rather than the argument itself. It is a fallacy, because how an idea originated is irrelevant to its validity.
Loaded words
• "Hitler summons war lords!”
• "Scotland stole a goal in the first half, but England's efforts were rewarded. . ."
--Loaded words: (also emotive argument)The deliberate use of prejudiced terms to conjure a more favorable or hostile response.
Wishful thinking
• "The credit card company will take my late fee off. Otherwise I'll be so broke I can't pay them anything."
--Wishful thinking:Rejecting a claim solely because
we do not wish it to be true.
Confirmation bias• Since I saw two people with the same birthday,
then I think that this classroom has an unusual number of people with the same birthday.
• So, the next time I see two people with the same birthday, then it will confirm my hypothesis.
• ---------------------------------• Confirmation Bias: Using future instances to
confirm one’s hypotheses, without appeal to independent evidence.
• Also, a tendency to search for or interpret new information in a way that confirms one's preconceptions.
• Avoiding information and interpretations which contradict prior beliefs.
• Fiber one commercial: http://www.youtube.com/watch?feature=endscreen&NR=1&v=ATU21AWw5yI
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composition
• "This must be a good orchestra because each member is a talented musician."
Composition:Claiming that what is true for individual
members of a class is also true for the class as a whole.
division
• "Germany is a militant country. Thus, each German is militant.”
• "Because the brain is capable of consciousness, each neural cell in the brain must be capable of consciousness."
Division:Attributing to the individuals in a group
something that is only true of the group as a unit.
Hasty Generalization
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Unrepresentative sample
• The apples on the top of the box look good. The entire box of apples must be good.
--Unrepresentative sample:The sample used relevantly different
from the population as a whole.
• "I'm backing Hillary Clinton on this one. She can't be wrong all the time.”
• “I’m betting red on the Roulette table. The last five times was black, so it’s bound to be red soon.”
--Gambler's Fallacy:Believing the next outcome
will somehow be influenced by the last outcome.This only applies to cases of independent trials, like rolling the dice.
Gambler’s fallacy
• "It cleans your teeth white! Yes, that's right-- whiter than white!"
-- Argumentum ad Nauseum:Repetition of a point,
often by exaggerating or slightly changing the point.
equivocation
• "All child-murderers are inhuman, thus, no child-murderer is human.”
• "My dog's got no nose/ How does he smell?/ Terrible!"
•Equivocation:Using words ambiguously;
equivocal words have more than one meaning.
equivocation
• “You are not entitled to your opinion.”
•Equivocation:Using words ambiguously;
equivocal words have more than one meaning.
LINGUISTIC FALLACIES
• 1. If someone is entitled to an opinion then her opinion is well-supported by the evidence. (This is precisely what it means to be entitled to an opinion).
• 2. I am entitled to my opinion (as is everyone in a democratic society).
• 3. Therefore, my opinion is well supported by the evidence.
FORMAL FALLACIES
• Consider the true premise: If there is fire, oxygen is present.
"Oxygen is present, therefore there is fire.”
"If I drop an egg, it breaks. This egg is broken, so I must have dropped it."
•--Affirming the consequent: (Remember: biconditional)
• Believing that the consequent (the second phrase)
necessarily entails the antecedent.
FORMAL FALLACIES
• Consider the premise: If there is fire, oxygen is present.
• There is no fire, therefore there is no oxygen.
• Consider the premise: If I am hungry in the morning, I will eat breakfast.
• I am not hungry in the morning, therefore I will not eat breakfast.
--Denying the antecedent:Believing that when the antecedent is false,
the consequent must be false also.
amphiboly• "I met the ambassador riding his horse. He was
snorting and steaming, so I gave him a lump of sugar"
• "Helicopter powered by human flies"• "The anthropologists went to a remote area and
took photographs of some native women, but they weren't developed."
• "One morning I shot an elephant in my pajamas. How he got into my pajamas I'll never know." --Groucho Marx
-- Amphiboly:
Sentence constructions are ambiguous; the whole meaning of a
statement can be taken in more than one way.
