Common Logical Fallacies

Common Logical Fallacies http://www.youtube.com/watch?v=k3jt5ibfRzw

Logical Fallacies… • Flaws in an argument • Often subtle • Learning to recognize these will: • Strengthen your own arguments • Help you critique other’s arguments

Important Terms • Argument: A conclusion together with the premises that support it. • Premise: A reason offered as support for another claim • Conclusion: A claim that is supported by a premise. • EXAMPLE: Whichever basketball team scores the most points will win the game. UK scored more points than UNC therefore UK won the game. ArgumentPremiseClaim

Important Terms • Valid: An argument whose premises genuinely support its conclusion • Unsound: An argument that has at least one false premise • Fallacy: An argument that relies upon faulty reasoning

Fallacy: Hasty Generalization • A generalization based on insufficient or unrepresented evidence • Deaths from drug overdoses in Metropolis have doubled over the last three years. Therefore, more Americans than ever are dying from drug abuse. • Dr. Spencer, a scientist at UK, doesn’t think that humans are causing global warming. Therefore, humans are probably not causing global warming.

Fallacy: Non Sequitur (Does Not Follow) • A conclusion that does not follow logically from preceding statements or that is based on irrelevant data. • Mary loves children, so will make an excellent school teacher.

“Either… or” Fallacy • The suggestion that only two alternatives exist when in fact there are more. • Either learn how to program a computer, or you won’t be able to get a decent job after college. • Either you’re a Republican, or you’re socialist and un-American!

Fallacy of False Cause • Labeling one thing as the cause of another thing on insufficient or unrepresentative evidence or using evidence that conflicts with established higher-level truths or theories. • Since Governor Smith took office, unemployment for minorities in the state has decreased by seven percent. Governor Smith should be applauded for reducing unemployment among minorities. • Dan White ate a lot of Twinkies and then killed the Mayor of San Francisco. If I were a mayor, I’d ban Twinkies so no one would kill me.

Fallacy of Circular Reasoning/ Begging the Question (Unsupported Assertion) • An argument in which the writer, instead of applying evidence simply restates the point in other language. • Students should not be allowed to park in lots now reserved for faculty because those lots should be for faculty only. • I’m the boss because I said I’m the boss.

Bandwagon Appeal (Ad Populum) • A claim that an idea should be accepted because a large number of people favor it or believe it to be true. • Everyone knows that smoking is physically addictive and causes bodily harm.

Ad Hominem (Argument to the person) • An attack on the person proposing an argument rather than on the argument itself. • Senator Jones was a conscientious objector during the Vietnam War, so his proposal to limit military spending has no merit. • Tom dresses like a nerd! How could he run for president of student council?

Red Herring Fallacy • An argument that focuses on an irrelevant issue to detract attention from the real issue. • Reporters are out to get the president, so it’s no wonder we are hearing rumors about these scandals. • You say that Coach Smith pressured teachers to give his students passing grades. But don’t you agree that athletics are important to schools? Don’t they build character?

False Authority (Testimonial) • This fallacy consists of an appeal to irrelevant authority, that is, an ‘authority’ who is not an authority in the field of question (or at least one we have no reason to believe to be such an authority). • Oprah says that she won’t eat beef, therefore you shouldn’t eat beef. • I bought a Harley Davidson because Arnold Schwarzenegger says it’s the best motorcycle.

Undistributed Middle Fallacy • An error in deductive reasoning in which the parts of a premise may, or may not, overlap. The middle term is undistributed in that all instances of a conclusion are also instances of the premise. • Valid argument: All mammals have hair. All whales are mammals. All whales have hair. • The middle term is distributed: Whales fits into the categories of “mammals” and “having hair.” • Undistributed Middle: All whales have hair. All humans have hair. All whales are human. • Undistributed: The middle term (Human) does not fit into both categories (Whales and Hair).

Ad populum/Bandwagon http://www.cafepress.com

Circular reasoning http://www.cafepress.com

Either/Or http://www.cafepress.com

http://www.youtube.com/watch?v=fUdkzk4kNx0 http://www.youtube.com/watch?v=tbVPblOmBqk

Try It! • Ladies and gentlemen of the jury, look at the bloody clothes, the murder weapon. Imagine the helpless screams of the victim. Such a crime deserves no verdict except guilty, guilty! • Red herring. The fact that the crime was horrible doesn’t imply the defendant’s guilt.

Try it! • I’m not a doctor, but I play a doctor on TV, and I wouldn’t dream of using anything but Tylenol for my toughest headaches. • Appeal to inappropriate authority. More commonly (in this case) known as quackery.

Try it! • You can hardly blame President Clinton for having extramarital affairs. Many presidents, when faced with similar situations, have yielded to the same temptations. • Red herring. The fact that others have had affairs is not really relevant to whether or not Clinton ought to be blamed for having affairs.

Try it! • There are more laws on the books than ever before, and more crimes are being committed than ever before. Therefore, to reduce crime, we must eliminate the laws. • False cause. The mere fact that more crime followed the creation of more laws does not entail that the new laws caused more crime. (Interestingly, the argument does work in one sense: Eliminating laws would reduce crime since, by definition, something is a crime only if it is against the law. So no laws would equal no crime.)

Try it! • Do most Americans believe in God? To find out, we asked over 10,000 scientists at colleges and universities throughout America. Less than 40 percent said they believed in God. The conclusion is obvious: Most Americans no longer believe in God. • Hasty Generalization (unrepresentative sample). The sample is pretty unrepresentative of the general American public.

Try it! • Many people criticize Thomas Jefferson for being an owner of slaves. But Jefferson was one of our greatest presidents, and his Declaration of Independence is one of the most eloquent pleas for freedom and democracy ever written. Clearly these criticisms are unwarranted. • Red herring. The fact that Jefferson was a great president has nothing to do with whether he ought to be condemned for owning slaves.

Jake, Kyle and Rolf are all members of the UNCP Young Republicans, and they are all planning to be Roman Catholic priests. Emma is also a member of the UNCP Young Republicans, so she is probably planning to be a Roman Catholic priest, too. • Questionable use of statistics (unrepresentative sample). Also suppressed evidence. Leaves out the fact that Roman Catholic priests are all male. The argument looks a little bit like an undistributed middle, but the form is slightly different. Here the form is • A is a C and a D. • B is a C. • Therefore B is probably also D. • This is an argument from analogy rather than a deductive argument. The deeper problem is that the analogy is bad (A and B are unalike in an importantly different way).

Try it! • The Soviet Union collapsed after taking up atheism. Therefore, we must avoid atheism for the same reasons. • False cause. The speaker assumes that taking up atheism caused the collapse of the Soviet Union without providing any evidence of a causal connection.

try it! • You’re a vegetarian? You do realize that Hitler was a vegetarian, too? • Generalization. The fact that Hitler held a particular belief doesn’t make that belief wrong.

Credits Annenberg Public Policy Center (2008). Monty Python and the Quest for the Perfect Fallacy. Retrieved 10-1-08 from http://www.factchecked.org/LessonPlanDetails.aspx?myId=7. Hacker, D. (1999). A Writer’s Reference, 4th ed. New York: Bedford/St. Martins. Mike, H. B. (1999). Language and Logic. Dubuque, Iowa: Kendall/Hunt Publishing, 1999. Wheeler, K. (2008). Logical fallacies handlist. Retrieved 10-1-08 from http://web.cn.edu/kwheeler/fallacies_list.html Many thanks to Shawn Mole for providing much of the condensed research. http://www.annenbergclassroom.org/pages.aspx?name=monty-python-and-the-quest-for-the-perfect-fallacy&AspxAutoDetectCookieSupport=1

Common Logical Fallacies