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Logical Fallacies

Logical Fallacies

Jan 03, 2016




Logical Fallacies. Statistics - Basics. Who Why How When Where What. Statistics - Vague Logos?. Guessing? Definition(s)? Measurement(s)? Sampling?. Statistics - Vague Language. “some” “many”. Statistics - MoE. Sampling Error: “±N%” where N might equal 3 Percentages: - PowerPoint PPT Presentation
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Page 1: Logical Fallacies

Logical Fallacies

Page 2: Logical Fallacies

Statistics - Basics

▪ Who

▪ Why

▪ How

▪ When

▪ Where

▪ What

Page 3: Logical Fallacies

Statistics - Vague Logos?

▪ Guessing?

▪ Definition(s)?

▪ Measurement(s)?

▪ Sampling?

Page 4: Logical Fallacies

Statistics - Vague Language

▪ “some”

▪ “many”

Page 5: Logical Fallacies

Statistics - MoE

▪ Sampling Error: “±N%” where N might equal 3

▪ Percentages:▪ In September, Candidate A received 42%▪ In September, Candidate B received 44%

▪ In August, Candidate A received 45%▪ In August, Candidate B received 42%

▪ Polls:▪ Sampling▪ MoEs▪ Comparison

Page 6: Logical Fallacies

Confirmation Bias

▪ When trying to determine the validity of

an assertion:

▪ Information search is highly biased towards

finding confirming evidence (gathering)

▪ Information search terminates too quickly


Page 7: Logical Fallacies

Look for Common Biases

▪ I read a report in the newspaper claiming

that women are worse drivers than men.

Do I believe the report?

▪ Yes… because of my friend Carrie

▪ No… because I’m a woman and I’m a good driver

▪ Should we drill for oil in Alaska?

▪ What does *** think?

Page 8: Logical Fallacies

Logical Fallacies - Examples

Page 9: Logical Fallacies

Example . . .

…[T]he acceptance of abortion does not end with the killing

of unborn human life. It continues on to affect our

attitude toward all aspects of human life. This is most

obvious in how quickly, following the acceptance of

abortion, comes the acceptance of infanticide―the killing

of babies who after birth do not come up to someone's

standard of life worthy to be lived―and then on to

euthanasia of the aged. If human life can be taken before

birth, there is no logical reason why human life cannot be

taken after birth.

▪ Source: Francis A. Schaeffer, "It is Your Life that is Involved", Who is For Life? (1984), p. 39.

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Slippery Slope

Page 11: Logical Fallacies

Example . . .

Hate based on skin color and/or ethnic and cultural differences still festers among us. It's an aggressive monster that actively seeks putrefaction like itself so it may commune and spawn. It spreads like a fungus, seeking to multiply.

The Internet has been a fertile ground for groups to plant evil seeds. As ways to interact on the Internet have grown, so grow the hate groups. Online communities, which so innocently attempt to bring like-minded individuals together for virtual socializing, created a nice breeding ground for venom.

Source: "Google Should Act", Contra Costa Times, 3/10/2005

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Begging the Question

… or Circular Reasoning

Page 13: Logical Fallacies

Example . . .

…Scientology textbooks sometimes refer to psychiatry as a "Nazi science".

Well, look at the history. Jung was an editor for the Nazi papers during World War II. … Look at the experimentation the Nazis did with electric shock and drugging. Look at the drug methadone. That was originally called Adolophine. It was named after Adolf Hitler.

Source: "Q&A: Tom Cruise", Entertainment Weekly, 6/9/2005

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False Analogy - or Guilt by Association

Page 15: Logical Fallacies

Example . . .

We hated the war, but we loved it too. Vietnam made us special, a generation with a mission. Vietnam gave the semblance of moral shape to what was actually a formless hatred of "the system." The war justified every excess, every violent thought and deed. Heaving a rock at some corporation's window, we banished guilt by the thought: This is for the Vietnamese. Trying to set fire to a university library, we said to ourselves: This is for the Vietnamese. If the war gave us license, it also gave us an addictive sense of moral superiority: we were better than the circumstances in which we were forced to live. If we committed small misdemeanors of indecency, they were in the long run justified by the much larger and more obscene crime in Southeast Asia.

Source: Peter Collier, "Something Happened to Me Yesterday", in Destructive Generation: Second Thoughts

About the Sixties, with David Horowitz (Summit Books, 1989), p. 264.

Page 16: Logical Fallacies

Red Herring

Attempting to justify committing a wrong

on the grounds that someone else is

guilty of another wrong is clearly a Red


Page 17: Logical Fallacies

Example . . .

The case of the ecologist who linked the cycles of the Canadian lynx and its prey, the snowshoe rabbit, with the sunspot cycle is instructive. The ecologist analyzed records of the Hudson Bay Company, which had been collecting pelts of the two species since 1735; he found that the two populations fluctuated up and down, displaying a periodicity of approximately ten years. Not surprisingly, the variations in the predatory lynx population tended to follow the ups and downs in the rabbit population with a time lag of a couple of years.

Then the ecologist superimposed the two curves atop a similar graph representing the concurrent sunspot activity: voilà! The three cycles approximately coincided over a good portion of their range. The ecologist leaped to the conclusion that the annual fluctuations of the lynx and rabbit populations were controlled by the eleven-year sunspot cycle….

Source: Lawrence E. Jerome, "Astrology: Magic or Science?", in Objections to Astrology by Bart J. Bok & Lawrence E. Jerome (Prometheus, 1975), p. 57.

Page 18: Logical Fallacies

Post hoc

"With this, therefore because of this" (Latin)

Page 19: Logical Fallacies

Example . . .

Instead of beating your chest over the current political-

contribution system, why don't you advocate a solution?

The last thing our political system needs is Time magazine

sermonizing about "how the little guy gets hurt." I'm sure

there are a lot of "little guys" in the magazine business

that have been flattened by Time's fat feet too.

Source: Rob Windoffer, Chicago, "Letters", Time, February 28, 2000.

Page 20: Logical Fallacies

Two fallacies . . .

▪ Ad hominem

▪ Tu quoque

Page 21: Logical Fallacies

Example . . .

There are very few general laws of social science, but we can offer one that has a deserved claim: the restriction of the concept of humanity in any sphere never enhances a respect for human life. It did not enhance the rights of slaves, prisoners of wars, criminals, traitors, women, children, Jews, blacks, heretics, workers, capitalists, Slavs or Gypsies. The restriction of the concept of personhood in regard to the fetus will not do so either.

Source: Phillip Abbott, quoted by Helen M. Alvaré in "Abortion is Immoral", from The Abortion Controversy,

Greenhaven, 1995, p. 25.

Page 22: Logical Fallacies

Begging the question

When writers assume as evidence for their argument the very conclusion they are attempting to prove

Page 23: Logical Fallacies

Example . . .

How do we know that we have here in the Bible a right

criterion of truth? We know because of the Bible's claims

for itself. All through the Scripture are found frequent

expressions such as "Thus says the Lord," "The Lord

said," and "God spoke." Such statements occur no less

than 1,904 times in the 39 books of the Old Testament.

Source: Gilbert W. Kirby, "Is the Bible True?" Decision, Vol. 1, Jan. 1974, p. 4. Cited by S. Morris Engel in Analyzing

Informal Fallacies, Prentice-Hall, 1980, p. 55.

Page 24: Logical Fallacies

Begging the question

Page 25: Logical Fallacies

Example . . .

… Quebec environment minister Lise Bacon

pledged the PCBs would be moved out and

broken down somehow within 18 months. She

also said that PCBs couldn't be all that

dangerous because her father had washed his

hands in PCBs but lived to an old age.

Source: Merritt Clifton, "PCB Homecoming", Greenpeace, November/December, 1989,

p. 21.

Page 26: Logical Fallacies

Hasty Generalization

“In understanding and characterizing

general situations, a logician cannot

normally examine every single example.

However, the examples used in inductive

reasoning should be typical of the

problem or situation at hand.”

Page 27: Logical Fallacies

Example . . .

[The Mayor] said the biggest problem for the city

administration has been fighting people who have

protested such things as industrial development.

"We've had people fight highways, the school

corporation and county zoning," he said. "I didn't

notice any of these people coming up here on

horses and donkeys. They all drove cars up here,

spewing hydrocarbons all over the place."

Source: Terre Haute Tribune-Star

Page 28: Logical Fallacies

Multiple -

▪ As hominem

▪ Two wrongs don’t make a right

▪ Tu quoque

Page 29: Logical Fallacies

Example . . .

…[H]igh-density development [doesn't] reduce congestion. The superficially appealing idea is that if we all live closer to where we work and shop, shorter car trips and mass transit will replace all those long car rides. But the real world doesn't work that way. Try this thought experiment. What happens at a cocktail party when a new wave of people shows up and the population density of the living room doubles? Is it harder or easier to get to the bar and the cheese tray? Is it harder or easier to carry on conversation and move around the room? As urban population density rises, auto-traffic congestion gets worse, not better, and commute times get longer, not shorter.

Source: Steven Hayward, "Suburban Legends", National Review, March 22, 1999, p. 36.

Page 30: Logical Fallacies

Weak Analogy

Page 31: Logical Fallacies

Example . . .

Ad in Food and Wine for American Express, showing comedian Jerry Seinfeld with a number of presumably new purchases--an armchair, a globe, a laptop computer, a mountain bike, and so forth: “A Cardmember Goes Shopping. The American ExpressR is welcome at all kinds of places. Just ask Jerry, who uses his Card for everyday items, as well as for the things that make him, well, Jerry. In fact, it’s so widely accepted, Jerry uses it wherever he goes. No kidding.”

Page 32: Logical Fallacies

Appeal to Authority

Page 33: Logical Fallacies

Example . . .

It’s important that every family be

protected by a whole life-insurance plan.

After all, what would happen if you died?

Your family would be destitute and would

probably end up on welfare.

Page 34: Logical Fallacies

Appeal to Fear

Page 35: Logical Fallacies

Example . . .

If colleges and universities continue to

admit large numbers of minorities under

affirmative action, soon there won't be

any room for whites.

Page 36: Logical Fallacies


▪ Genetic (racist)

▪ Slippery Slope

Page 37: Logical Fallacies

Example . . .

This was a commonly-heard argument after the September 11 terrorist attacks: Everybody, with one exception, in the U.S. Congress voted to support the administration’s decision to bomb Afghanistan after the September 11 attacks on New York’s World Trade Center and the Pentagon. The lone dissenter was Barbara Lee, who represents Berkeley. It’s outrageous that she had the temerity to vote against her colleagues. She’s completely out of step with the rest of the country, since the nation is 100% behind the bombing campaign.

Page 38: Logical Fallacies


… and Appeal to Patriotism

Page 39: Logical Fallacies

Example . . .

Store advertisement: Why not join the

other discriminating shoppers and buy

your china, crystal, and silver at

“Remember When”?

Page 40: Logical Fallacies

Appeal to Flattery

… and Snob Appeal/Bandwagon

Page 41: Logical Fallacies

Example . . .

When Oliver North and John Poindexter

admitted that they were committing

illegal acts when they plotted to sell arms

to Iran and divert money to the Contras

during the Irangate scandal, they

defended their actions out of love for

their country.

Page 42: Logical Fallacies

Appeal to Patriotism

Page 43: Logical Fallacies

Example . . .

Highway sign: “Stop in at Grandma’s Diner and

relax over a home-cooked meal. Enjoy

Grandma’s famous meatloaf and mashed

potatoes in a casual, friendly atmosphere.

We’ll make you feel as if you’re right at


Page 44: Logical Fallacies

Appeal to Tradition

Page 45: Logical Fallacies

Example . . .

How could an employer be so cruel as to fire a

worker like Robert Gonzalez? Of course, his

absenteeism has been significant, and he has

difficulty getting to work on time. And it’s true

that customers have complained about his

rudeness. But he has seven children to support,

house payments to make, and college loans to


Page 46: Logical Fallacies

Appeal to Sympathy

Page 47: Logical Fallacies

Example . . .

What was Mayor Shelton thinking of when she

came up with a plan to build a shopping center

along the only open space fronting the ocean

in Princeton-by-the-Sea? Any idiot can see that

her proposal is absurd.

Page 48: Logical Fallacies


Page 49: Logical Fallacies

Example . . .

I’m not voting for Mayor Shelton’s idea of

building a shopping center along the

only open space fronting the ocean in

Princeton-by-the-Sea! She spends far too

much money on clothes for me to trust

her with my money!

Page 50: Logical Fallacies

Ad hominem

Page 51: Logical Fallacies

Example . . .

“More than 50 dangerous pesticides

contaminate Britain’s food, official tests reveal.

[…] The revelation – in a survey of official

testing results – will heighten concern about

food contamination.”

Geoffrey Lean, the Independent on Sunday 27 February 2005

Page 52: Logical Fallacies

Multiple -

▪ Appeal to Fear

▪ Out of Context

Page 53: Logical Fallacies

Example . . .

“Think about it: every time there’s a list of the

100 greatest records of all time, all those

albums were recorded in two days.

Jack White, the White Stripes, Observer Music Monthly November 2004

Page 54: Logical Fallacies

Hasty Generalization

Page 55: Logical Fallacies

Example . . .

I have been a member of the NAACP for ten

years. My son cannot possibly be a bigot.

Page 56: Logical Fallacies

Argument from Adverse Causes

Page 57: Logical Fallacies

Example . . .

I guess I will receive a C on my next English

paper because the teacher said my average

was a C so far, so the chances must be that I'll

get a C on the next one.

Page 58: Logical Fallacies

Non sequitur

▪ It does not follow (Latin)

Page 59: Logical Fallacies

Friedrich Nietzche's attack on social welfare should not be taken seriously. He is said to have been a degenerate and it is a fact that he went insane.

You can be sure of getting the best watch possible if you buy a Tempus Fugit watch, because you will be buying the world's greatest watch.

Rare taste: you either have taste or you don't. (Scotch ad)

Page 60: Logical Fallacies

You will get pregnant if you kiss a boy. I've seen Sally kiss boys three times, and now she is pregnant.

My honesty is a matter of record. My enemies have tried to bring similar charges against me before, but they couldn't prove anything that stands up in court. That proves I am an honest man.

Just answer the question yes or no. Were you still selling drugs when you came to this town?

Page 61: Logical Fallacies

How can you justify giving this man life imprisonment by declaring him guilty of murder? After all, since that time he has become a devout Christian and proven to be an exemplary prisoner during the whole time he was on trial.

Senator Jones shouldn't be blamed for having sex with teenage girls. After all, other senators have done much worse things.

American citizens must raise taxes to support schools. Without more money, our schools cannot possibly do a good job.

Page 62: Logical Fallacies

The pinkos, socialistic liberals, and weirdos in that other department are naturally against my legislative reforms.

I interviewed the entire third floor of my dorm, and my research shows that most of the people at this university go home on weekends.

He is using unfair arguments because none of his arguments are equitable. Because they are not equitable, they are not just, and hence, unfair.

Page 63: Logical Fallacies

Alien abductions must take place because no one has found any evidence to disprove the eye-witness accounts.

We must put God back in our schools, or else American society will degenerate.

You cannot listen to Rush Limbaugh's ideas because he is a conservative. Conservative speaker's ideas are not worth listening to. Since Limbaugh is conservative, you cannot listen to his ideas.

Page 64: Logical Fallacies


▪ Moment

▪ Vernon Robinson for Congress