QUESTION OF THE DAY: TAKE A LOOK AT THE ALGEBRA PROOF BELOW, AND COPY IT DOWN IN YOUR NOTES.

CHALLENGE: THE FINAL LINE CAN’T BE CORRECT! CAN YOU TELL WHAT WENT WRONG??

If we advance to the next slide too soon, usea copy of the presentation to make notes.

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Prologue

Recognizing Fallacies

ARGUMENT

An argument is a set of facts or assumptions, called premises, that support a conclusion.

Argument ExamplesIn the below arguments, identify the premise(s) and conclusion.

• Everyone in San Francisco is a liberal.• Michael Savage lives in San Francisco.• Michael Savage is a liberal.

• All US Presidents have been men.• JFK was a man.• JFK was a US President.

People generally quarrel because they cannot argue.

G.K. Chesterton (1874-1936)

LOGICLogic is a branch of mathematics that studies the methods and principles of reasoning.

Studying Logic enables one to learn how to create valid arguments, reason clearly, and develop excellent critical thinking skills. These skills will allow you to interpret and analyze events in every area of life.

FALLACIES

A fallacy is a deceptive, misleading, or unsound argument—an argument in which the conclusion is not well supported by the premises.

Some arguments are invalid. There is an error in reasoning. Such an argument is called a fallacyfallacy.

FALLACY STRUCTURES• Appeal to Popularity• False Cause• Appeal to Ignorance• Hasty Generalization• Limited Choice

• Appeal to Emotion• Personal Attack• Circular Reasoning• Diversion• Straw Man

Remember, all fallacies contain faulty reasoning. That is, the conclusion does not follow logically from the premises.

APPEAL TO POPULARITYThe fallacy of appeal to popularity (or appeal to majority) uses the fact that large numbers of people believe or act some way as evidence that the belief is correct.

*Many people believe p is true; therefore ……p is true.

EXAMPLE 1: Microsoft makes the best computer operating system. After all, more people use Windows than any other operating system.

APPEAL TO POPULARITY

EXAMPLE 2: Ford makes the best automobile in America; after all, more people drive Fords than any other American car.

FALSE CAUSE

The fallacy of false cause uses the fact that one event came before another as evidence that the first event caused the second event.

*A came before B; therefore . . . A caused B.

EXAMPLE 1: Timmy took some cold medication before his math test. He made a 100 on the test. The cold medication made Timmy ace his math test.

FALSE CAUSE

EXAMPLE 1: “I placed a quartz crystal on my forehead, and in five minutes my headache was gone. The crystal made my headache go away.”

APPEAL TO IGNORANCEThe fallacy of appeal to ignorance uses ignorance (lack of knowledge) about the truth of a proposition to conclude the opposite.

*There is no proof that p is true; therefore . . . p is false.

EXAMPLE 1: Scientists have not found any evidence of Bigfoot. Therefore, anyone who claims to have seen Bigfoot must be hallucinating.

*An absence of evidence is not evidence of absence.*

APPEAL TO IGNORANCEEXAMPLE 2: Scientists have not proved that global warming will have any bad consequences for the human race. Therefore, the global warming catastrophes that people are talking about will never happen.

HASTY GENERALIZATIONThe fallacy of hasty generalization draws a conclusion from an inadequate number of cases or cases that have not been sufficiently analyzed.

*A and B are linked one or a few times; therefore . . . … A causes B (or vice versa).

EXAMPLE 2: Three cases of brain cancer have occurred in people who use cell phones. Therefore, cell phones must cause brain cancer.

LIMITED CHOICEThe fallacy of limited choice artificially precludes choices that ought to be considered.

*p is false; therefore . . . only q can be true.

EXAMPLE 1: “You don’t support the President, so you are not a patriotic American.”

EXAMPLE 2: “Have you stopped smoking?”

In court, this is called ‘Leading the Witness’.

EXAMPLE 3: “You’re wrong, so I must be right.”

APPEAL TO EMOTIONThe fallacy of appeal to emotion uses an emotional reaction (instead of logic) as a tool of persuasion.

*p is associated with an emotional response; therefore . . . p is true.

EXAMPLE 1: In a commercial for Michelin tires, a picture of a baby is shown with the words “because so much is riding on your tires.”

EXAMPLE 2: If my opponent is elected, your tax burden will rise.

PERSONAL ATTACKThe fallacy of personal attack (ad hominem) uses a dislike of a person or group making an argument to conclude the argument is not valid.

*I have a problem with the person or group claiming p; therefore . . . p is not true.

EXAMPLE 1: There is no way Senator Smith’s bill can help the cause of gun control because he is one of the biggest recipients of campaign contributions from the National Rifle Association.

The provisions of the Senator’s bill were not challenged.

PERSONAL ATTACK

EXAMPLE 2:

Mike: “Tom, you should stop drinking because it is hurting your grades, endangering people if you drive, and hurting your relationship with your family.”

Tom: “I’ve seen you drink a few on occasion yourself.”

CIRCULAR REASONINGThe fallacy of circular reasoning just restates the premise in different words.

*p is true; p is restated in different words.

EXAMPLE: Schools must implement a zero tolerance policy toward drug use, because any tolerance of drugs is unacceptable.

DIVERSIONThe fallacy of diversion (or red herring) diverts the attention from one issue, p, to another (related) issue, q.

*p is related to q and I have an argument concerning q; therefore . . . p is true.

EXAMPLE: We should not drill for oil in the Alaskan National Wildlife Refuge (ANWR), because we have too many gas-guzzling automobiles as it is.

DIVERSIONThe term “red herring” is traced back to the 19th century, when British fugitives discovered they could divert bloodhounds from their pursuit by rubbing a red herring across their trail.

STRAW MANThe fallacy of straw man makes an argument based on a distortion of someone’s words or beliefs.

*I have an argument concerning a distorted version of p; therefore . . . I hope you are fooled into concluding that I have an argument concerning the real version of p.

EXAMPLE: The mayor of a large city has proposed decriminalizing drug possession in order to reduce overcrowding in jails. His challenger in the upcoming election says, “The mayor doesn’t think there’s anything wrong with drug use, but I do.”

DUE NEXT CLASS:

Write two paragraphs about the following:

Describe an instance in which you were persuaded of something that you later decided was untrue. Explain how you were persuaded and why you later changed your mind.

Did you fall victim to any fallacies? If so, how might you prevent the same thing from happening in the future?

PLEASE TYPE OR WRITE NEATLY. IDENTIFY THE FALLACY YOU ARE DESCRIBING. I WILL NOT GRADE SPELLING, GRAMMAR, ETC.