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Watch Out for Common Fallacies

Ambiguity Fallacies


AMPHIBOLY:
A fallacy of syntactical ambiguity deliberately misusing implications. Example: "Three out of four doctors recommend this type of pain relief!" The implied assertion here is that three out of four means seventy-five percent of all doctors and that this type of pain relief means this particular pain reliever.

EQUIVOCATION
: This fallacy is a product of semantic ambiguity. The arguer uses the ambiguous nature of a word or phrase to shift the meaning in such a way as to make the reason offered appear more convincing. Example: An ad from a sugar company says "Sugar is an essential component of the body, a key material in all sorts of metabolic processes, so buy some P&R sugar today." The word "sugar" is being used with two definitions that the ad does not acknowledge.


Appeals
to Motive in Place of Support Fallacies


APPEAL TO EMOTION:
In this fallacy, the arguer uses emotional appeals rather than logical reasons to persuade the listener. The fallacy can appeal to various emotions including pride, pity, fear, hate, vanity, or sympathy. The appeal to sympathy is actually a formal fallacy labeled Ad Misericordiam. Generally, the issue is oversimplified to the advantage of the arguer. Example: In 1972, there was a widely printed advertisement printed by the Foulke Fur Co., which was in reaction to the frequent protests against the killing of Alaskan seals for the making of fancy furs. According to the advertisement, clubbing the seals was one of the great conservation stories of our history, a mere exercise in wildlife management, because "biologists believe a healthier colony is a controlled colony."

COMMON BELIEF
: This fallacy is committed when we assert a statement to be true on the evidence that many other people allegedly believe it. Being widely believed is not proof or evidence of the truth. Example: Of course Nixon was guilty in Watergate. Everybody knows that.

PAST BELIEF
: A form of the COMMON BELIEF fallacy. The same error in reasoning is committed except the claim is for belief or support in the past. Example: Everyone knows that the Earth is flat, so why do you persist in your outlandish claims? 

SLANTING
: A form of misrepresentation in which a true statement is made, but made in such a way as to suggest that something is not true or to give a false description through the manipulation of connotation. Example: I can't believe how much money is being poured into the space program (suggesting that 'poured' means heedless and unnecessary spending).


Category
Fallacies


COMPOSITION:
Because the parts of a whole have a certain property, it is argued that the whole has that property. That whole may be either an object composed of different parts, or it may be a collection or set of  individual members. Example: The brick wall is six feet tall. Thus, the bricks in the wall are six feet tall. or Conventional bombs did more damage in W.W. II than nuclear bombs. Thus, a conventional bomb is more dangerous than a nuclear bomb.

DIVISION:
This fallacy is committed when we conclude that any part of a particular whole must have a characteristic because the whole has that characteristic. Example: I am sure that Karen plays the piano well, since her family is so musical.


Causal
Fallacies


GENUINE BUT INSIGNIFICANT CAUSE:
The object or event identified as the cause of an effect is a genuine cause, but insignificant when compared to the other causes of that event. Example: Smoking is causing air pollution in our cities. (True, but the effect of smoking is insignificant compared to the effect of auto exhaust.) or By leaving your air conditioner on overnight you are contributing to global warming.

POST HOC ERGO PROPTER HOC
: A form of a hasty generalization in which it is inferred that because one event followed another it is necessarily caused by that event. Example: Mary joined our class and the next week we all did poorly on the quiz. It must be her fault.


Changing
the Subject Fallacies


ATTACKING THE PERSON or Ad Hominum
. Attacking the arguer rather than his/her argument. Saying something negative about someone is not automatically ad hominum. If a person (politician for example) is the issue, then it is not a fallacy. Example: John's objections to capital punishment carry no weight since he is a convicted felon.

APPEAL TO AUTHORITY or Ad verecuniam.
This fallacy tries to convince the listener by appealing to an expert. Often times it is an authority in one field who is speaking out of his field. Example: Sports stars selling cars or hamburgers. Or, the actor on a TV commercial that says, "I'm not a doctor, but I play one on TV."


Definition
Fallacies


BEGGING THE QUESTION
: An argument in which the conclusion is implied or already assumed in the premises. Also said to be a circular argument. Example: Of course the Bible is the word of God. Why? Because God says so in the Bible.

CIRCULAR DEFINITION:
The definition includes the term being defined as a part of the definition. Example: An animal is human if and only if it has human parents. (The term being defined is "human". But in order to find a human, we would need to find human parents. To find human parents we would already need to know what a human is.) or  A book is pornographic if and only if it contains pornography. (We would need to know what pornography is in order to tell whether a book is pornographic.)

Distraction
Fallacies

APPEAL TO IGNORANCE or Ad ignorantium.
Arguing on the basis of what is known and can be proven. If you can't prove that something is true then it must be false (and vice versa). Example: You can't prove there isn't a Loch Ness Monster, so there must be one.

FALSE DILEMMA
(often called the either/or fallacy because the argument nearly always includes the words "either... or..."). This fallacy assumes that we must choose between two opposite extremes instead of allowing for other possibilities, especially for the possibility of choosing an alternative between the extremes. Example: Women need to be either brilliant or beautiful to survive in this world.

SLIPPERY SLOPE
or : A line of reasoning in which there is no gray area or middle ground. It states that x, y, z are implicit in step a. The primary characteristic is that it fails to distinguish between (or among) degrees of difference. It argues for (or against) the first step because if you take the first step, you will inevitably follow through to the last. Example: We can't allow students any voice in decision-making on campus; if we do, it won't be long before they are in total control.


Explanation
Fallacies


QUESTIONABLE CAUSE.
The fallacy of questionable cause is committed when, on insufficient evidence, we identify a cause for an occurrence that has taken place or a fact that is true. Example: I can't find the checkbook; I am sure that my husband hid it so I couldn't go shopping today.

UNTESTABILITY:
The theory advanced to explain why some phenomena occurs cannot be tested. We test a theory by means of its predictions. For example, a theory may predict that light bends under certain conditions, or that a liquid will change color if sprayed with acid, or that a psychotic person will respond badly to particular stimuli. If the predicted event fails to occur, then this is evidence against the theory. 

A theory cannot be tested when it makes no predictions. It is also untestable when it predicts events which would occur whether or not the theory were true. Example: Aircraft in the mid-Atlantic disappear because of the effect of the Bermuda Triangle, a force so subtle it cannot be measured on any instrument. (The force of the Bermuda Triangle has no effect other than the occasional downing of aircraft. The only possible prediction is that more aircraft will be lost. But this is likely to happen whether or not the theory is true.) 


Inductive
Fallacies


ARGUMENT FROM ANALOGY
or FALSE ANALOGY: An unsound form of inductive argument in which an argument is based completely or relies heavily on analogy to prove its point. Example: This must be a great car, for, like the finest watches in the world, it was made in Switzerland.

FAR-FETCHED HYPOTHESIS:
A fallacy of inductive reasoning that is committed when we accept a particular hypothesis when a more acceptable hypothesis, or one more strongly based in fact, is available. Example: The African-American church was set afire after the civil rights meeting last night; therefore, it must have been done by the leader and the minister to cast suspicion on the local segregationists.

HASTY GENERALIZATION:
A generalization accepted on the support of a sample that is too small or biased to warrant it. Example: All men are rats! Just look at the louse that I married.


Missing
the Point Fallacies


CONTRARY TO FACT HYPOTHESIS:
This fallacy is committed when we state with an unreasonable degree of certainty the results of an event that might have occurred but did not. Example: If President Bush had not gone into the Persian Gulf with military force when he did, Saddam Hussein would not have controlled the world's oil from Saudi Arabia.

RED HERRING:
This fallacy introduces an irrelevant issue into a discussion as a diversionary tactic. It takes people off the issue at hand; it is beside the point. Example: Many people say that engineers need more practice in writing, but I would like to remind them how difficult it is to master all the math and drawing skills that an engineer requires.

STRAW MAN:
This fallacy occurs when we misrepresent an opponent's position to make it easier to attack, usually by distorting his or her views to ridiculous extremes. This can also take the form of attacking only the weak premises in an opposing argument while ignoring the strong ones. Example: Those who favor gun-control legislation just want to take all guns away from responsible citizens and put them into the hands of the criminals.

TWO WRONGS MAKE A RIGHT:
This fallacy is committed when we try to justify an apparently wrong action by charges of a similar wrong. The underlying assumption is that if they do it, then we can do it too and are somehow justified. Example: Supporters of apartheid are often guilty of this error in reasoning. They point to U.S. practices of slavery to justify their system.


Non
Sequitur Fallacies


AFFIRMING THE CONSEQUENT:
An invalid form of the conditional argument in which the second premise affirms the consequent of the first premise and the conclusion affirms the antecedent. Example: If he wants to keep the job, then he will work hard. He is working hard; therefore he wants to keep the job.

DENYING THE ANTECEDENT
: An invalid form of the conditional argument in which the second premise denies the antecedent of the first premise, and the conclusion denies the consequent. Example: If he wants to keep his job, he will work hard. He does not want that job, so he won't work hard.

INCONSISTENCY:
A discourse is inconsistent or self-contradicting if it contains, explicitly or implicitly, two assertions that are logically incompatible with each other. Inconsistency can also occur between words and actions. Example: A woman who demands equal rights and represents herself as a feminist, yet is upset when a date expects her to pay half.

NON SEQUITUR:
In this fallacy the premises have no direct relationship to the conclusion. This fallacy appears in political speeches and advertising with great frequency. Example: A waterfall in the background and a beautiful girl in the foreground have nothing to do with an automobile's performance.

Statistical Syllogism Fallacies


ACCIDENT:
A general rule is applied when circumstances suggest that an exception to the rule should apply. Example: The law says that you should not travel faster than 50 mph, thus even though your father could not breathe, youshould not have traveled faster than 50 mph

CONVERSE ACCIDENT:
An exception to a generalization is applied to cases where the generalization should apply. Example: Because we allow terminally ill patients to use heroin, we should allow everyone to use heroin.


Syllogism
Error Fallacies


FALLACY OF EXCLUSION:
Important evidence which would undermine an inductive argument is excluded from consideration. The requirement that all relevant information be included is called the "principle of total evidence." Example: Edward is a Floridian, and most Floridians vote Republican, so Edwards will probably vote Republican. (The information left out is that Edwards lives in Miami, and that most people in Miami vote Democrat.)

FALLACY OF DRAWING AN AFFIRMATIVE CONCLUSION FROM A NEGATIVE PREMISE:
The conclusion of a standard form categorical syllogism is affirmative, but at least one of the premises is negative. Examples: All mice are animals, and some animals are not dangerous, therefore somemice are dangerous. or No honest people steal, and all honest people pay taxes, so some peoplewho steal pay pay taxes.

ILLICIT MAJOR: The predicate term of the conclusion refers to all members of that category, but the same term in the premises refers only to some members of that category. Example: All Texans are Americans, and no Californians are Texans, therefore, no Californians are Americans. 

For more information and practice on fallacies look up these sites: 

Fallacies: The Internet Encyclopedia of Philosophy: http://www.iep.utm.edu/fallacy/

Fallacies on the Nizkor Project: http://www.nizkor.org/features/fallacies/

Fallacy Files: http://www.fallacyfiles.org/

How to Avoid Common Logical Errors:  
http://www.ehow.com/how-to_4845353_avoid-common-logical-errors.html

How to Avoid Logical Fallacies:
http://www.ehow.com/how_2149398_avoid-logical-fallacies.html