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LOGICAL FALLACIES

LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

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Page 1: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

LOGICAL FALLACIES

Page 2: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

LOGICAL FALLACIES

Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments or irrelevant points, and are often identified because they lack evidence that supports their claim.

Avoid these common fallacies in your own arguments and watch for them in the arguments of others.

Page 3: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

APPEALS TO AUTHORITY

Appeal to Authority: Instead of providing evidence the rhetor simply appeals to the respect people have for “experts.”

Testimony from an authority may be a fallacy unless:• The authority is actually an expert in a specific field• The authority is arguing a point well-accepted in the field• The authority is objective and unbiased.

Page 4: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

A COMMON APPEAL TO “AUTHORITY”

Appeal to Authority: Instead of providing evidence the rhetor simply appeal to the respect people have for the famous.

Matthew Mcconaughey saying he “just liked” a car doesn’t mean it’s a quality car.

What makes him an expert on cars?

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Page 5: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

STRAW MAN

Straw Man: This move oversimplifies an opponent's viewpoint and then attacks that hollow argument.

It is much easier to win an argument with a scarecrow than a reasonable opponent.

Page 6: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

STRAW MAN

Straw Man: This move oversimplifies an opponent's viewpoint and then attacks that hollow argument.

Original Argument: Texting and driving is dangerous and therefore texting drivers should be fined.

Straw-man Counter: These fines are insane! People need cell phones in cars to make emergency calls.

Page 7: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

CIRCULAR REASONING

Circular Argument: This restates the argument rather than actually proving it.

Example: Carpool lanes really improve traffic congestion because they greatly reduce the number of cars on the road.

Page 8: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

BEGGING THE QUESTION

Begging the Claim: The conclusion that the writer should prove is validated within the claim.

Example: Filthy, polluting hummers should be banned.

Page 9: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

SLIPPERY SLOPE

Slippery Slope: This is a conclusion based on the premise that if A happens, then eventually through a series of small steps, through B, C,..., X, Y, Z will happen too.

Basically equating A and Z. So, if we don't want Z to occur, A must not be allowed to occur either.

Example: If we ban Hummers because of environmental concerns eventually the government will ban all cars, so we should not ban Hummers.

Page 10: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

SLIPPERY SLOPE

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Page 11: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

ANOTHER SLIPPERY SLOPE

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Page 12: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

YET ANOTHER SLIPPERY SLOPE

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Page 13: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

HASTY GENERALIZATION

Hasty Generalization: This is a conclusion based on insufficient or biased evidence. In other words, you are rushing to a conclusion before you have all the relevant facts.

Example: My 80 year old grandmother got into a car accident last week. People over 80 shouldn’t be able to drive.

Page 14: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

POST HOC (ERGO PROPTER HOC)AKA CAUSE AND EFFECT FALLACY

Post hoc ergo propter hoc: translates to “After this, therefore because of this."

This is a conclusion that assumes that if 'A' occurred after 'B' then 'B' must have caused 'A.'

Example: I rode the light rail, and now I am sick. Riding the light rail must have made me sick.

Page 15: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

POST HOC (ERGO PROPTER HOC)AKA CAUSE AND EFFECT FALLACY

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Page 16: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

NON SEQUITUR: “DOES NOT FOLLOW”

Non Sequitur: translates to “Does not follow.” It means that a the rhetor has drawn a conclusion that does not logically follow the premises.

Premise 1: My neighbor’s Prius gets amazing gas mileage.Premise 2: My neighbor’s Prius has a sick paint job with flames.

Conclusion: If I get a sick new paint job on my car it will dramatically improve my gas mileage.

Page 17: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

GENETIC FALLACY

Genetic Fallacy: This conclusion is based on an argument that the origins of a person, idea, institute, or theory determine its character, nature, or worth.

Example: The Volkswagen Beetle is an evil car because it was originally designed by Hitler's army.

Page 18: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

EITHER /OR

Either/or: This is a conclusion that oversimplifies the argument by reducing it to only two sides or choices.

Example: We can either stop using cars or destroy the earth.

Page 19: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

AD HOMINEM

Ad hominem: This is an attack on the character of a person rather than his or her opinions or arguments.

Example: Green Peace’s proposal for fuel efficiency guidelines are a horrible idea because they are all dirty, lazy hippies.

Page 20: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

AD POPULUM

Ad populum: This is an emotional appeal that speaks to positive (such as patriotism, religion, democracy) or negative (such as terrorism or fascism) concepts rather than the real issue at hand.

Example: If you were a true American you would support the rights of people to choose whatever vehicle they want.

Page 21: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

BANDWAGON

Bandwagon: The argument that since something is popular or everybody is doing it, so should you. Think of peer pressure or popularity as being the basis of the argument. 

Example: You should buy a Toyota Camry. It has long been the best-selling car in America.

Page 22: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

RED HERRING

Red Herring: This is a diversionary tactic that avoids the key issues, often by avoiding opposing arguments rather than addressing them.

Example: The light rail system might improve traffic congestion, but think of all the hard working auto mechanics who could lose their jobs.

Page 23: LOGICAL FALLACIES. Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments

PUTTING IT ALL TOGETHER

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