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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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  • Logical Fallacies

  • Statistics - BasicsWhoWhyHowWhenWhereWhat

  • Statistics - Vague Logos?Guessing?Definition(s)?Measurement(s)?Sampling?

  • Statistics - Vague Languagesomemany

  • Statistics - MoESampling Error: N% where N might equal 3Percentages: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:SamplingMoEsComparison

  • Confirmation BiasWhen trying to determine the validity of an assertion:Information search is highly biased towards finding confirming evidence (gathering)Information search terminates too quickly (sampling)

  • Look for Common BiasesI read a report in the newspaper claiming that women are worse drivers than men. Do I believe the report?Yes because of my friend CarrieNo because Im a woman and Im a good driver

    Should we drill for oil in Alaska?What does *** think?

  • Logical Fallacies - Examples

  • 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 infanticidethe killing of babies who after birth do not come up to someone's standard of life worthy to be livedand 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.

  • Slippery Slope

  • 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

  • Begging the Question or Circular Reasoning

  • 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

  • False Analogy - or Guilt by Association

  • 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.

  • Red HerringAttempting to justify committing a wrong on the grounds that someone else is guilty of another wrong is clearly a Red Herring.

  • 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: voil! 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.

  • Post hoc"With this, therefore because of this" (Latin)

  • 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.

  • Two fallacies . . .Ad hominemTu quoque

  • 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. Alvar in "Abortion is Immoral", from The Abortion Controversy, Greenhaven, 1995, p. 25.

  • Begging the questionWhen writers assume as evidence for their argument the very conclusion they are attempting to prove

  • 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.

  • Begging the question

  • 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.

  • Hasty GeneralizationIn 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.

  • 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

  • Multiple - As hominemTwo wrongs dont make a rightTu quoque

  • 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.

  • Weak Analogy

  • 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, its so widely accepted, Jerry uses it wherever he goes. No kidding.

  • Appeal to Authority

  • Example . . .Its 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.

  • Appeal to Fear

  • Example . . .If colleges and universities continue to admit large numbers of minorities under affirmative action, soon there won't be any room for whites.

  • MultipleGenetic (racist)Slippery Slope

  • 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 administrations decision to bomb Afghanistan after the September 11 attacks on New Yorks World Trade Center and the Pentagon. The lone dissenter was Barbara Lee, who represents Berkeley. Its outrageous that she had the temerity to vote against her colleagues. Shes completely out of step with the rest of the country, since the nation is 100% behind the bombing campaign.

  • Bandwagon and Appeal to Patriotism

  • Example . . .Store advertisement: Why not join the other discriminating shoppers and buy your china, crystal, and silver at Remember When?

  • Appeal to Flattery and Snob Appeal/Bandwagon

  • 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.

  • Appeal to Patriotism

  • Example . . .Highway sign: Stop in at Grandmas Diner and relax over a home-cooked meal. Enjoy Grandmas famous meatloaf and mashed potatoes in a casual, friendly atmosphere. Well make you feel as if youre right at home.

  • Appeal to Tradition

  • 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 its true that customers have complained about his rudeness. But he has seven children to support, house payments to make, and college loans to repay.

  • Appeal to Sympathy

  • 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.

  • Ridicule

  • Example . . .Im not voting for Mayor Sheltons 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!

  • Ad hominem

  • Example . . .More than 50 dangerous pesticides contaminate Britains 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

  • Multiple -Appeal to FearOut of Context

  • Example . . .Think about it: every time theres 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

  • Hasty Generalization

  • Example . . .I have been a member of the NAACP for ten years. My son cannot possibly be a bigot.

  • Argument from Adverse Causes

  • 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.

  • Non sequiturIt does not follow (Latin)

  • 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)

  • 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?

  • 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.

  • 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.

  • 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.

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