A fallacy is essentially an error in reasoning. Sometimes, they are difficult to detect, because fallacious thinking often appears to be reasonable, and, because fallacies are so oft repeated, one may be tempted to believe them.  This only makes spotting and dismantling erroneous thinking all the more difficult.

Here is a list of some of the more common informal fallacies which plague us today.  Eventhough many of these examples are fictious, I apologize in advance if I happen to use one that has come up in an argument I've personally been involved.

Ad Hominem False Attribution
Ad Hominem-circumstantial False Dilemma
Ambiguity Faulty Comparison
Anachronism Genetic Fallacy
Anecdotal Evidence Hasty Conclusion
Appeal to Authority Hasty Generalization
Appeal to the Extreme Ignored Intention
Appeal to Ignorance Invincible Ignorance
Appeal to Nature Irrelevant Reasons
Appeal to Tradition Lack of Proportion
Appeal to Popularity Poisoning the Well
Appeal to Unknowable Statistics Provincialism
Begging the Question Questionable Cause
Bifurcation Red Herring
Circular Reasoning Relative Privation
Composition Slippery Slope
Division Suppressed Evidence
Emotional Appeals Tautology
Equivocation Two Wrongs Make a Right


Ad Hominem, "against the person"

Description: Reverse of the Appeal to Authority. The Ad Hominem argument rejects an idea based on who subscribes to or promotes it. It is also more commonly called a "personal attack"; instead of attacking the argument or position, the arguer is attacked. Note that all personal attacks are not fallacious. Sometimes the personal character of person does matter in an argument. For example, the fact that a politician is a known white collar criminal may just be relevant to a discussion of his re-election, even though that does not, in and of itself, invalidate the bill (his ideas) he has just introduced. 

Example: "I hear that the Texas senate passed a bill allowing the building of a governor's chapel in Austin. Texans sure are dumb."

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Ad Hominem-circumstantial

Description: Form of Ad Hominem. This is a case where the argument is rejected, not on the personality of an opponent but, on some circumstances which supposedly makes the arguer an unreliable source. While it is extremely important to understand the point of view of the person presenting an argument, where a person comes from, their social and economic situation and background, or even education level, these things do not directly effect the quality of the argument itself.

Example: "Hey, I hear our governor was once homeless. How could a homeless person know how to balance a budget, more less a multi-million dollar one?"

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Description: Any argument which does not account for multiple word or phrase meanings. 

Example: "The First National Bank has the highest interest in town." 

(Does the bank offer higher interest on savings accounts or does it charge more for a loan?)

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Description: An argument based on the faulty comparison of people, ideas or values from widely different time periods.

Example: "If segregation was good enough for my great grandfather, it's good enough for me."

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Anecdotal Evidence

Description: Drawing from an extremely small and unrepresentative sample, the arguer attempts to show that his position is true based on a second-hand report. While another individual's experiences may help to bolster or illustrate a position, they do not represent a wide enough sample to give us credible reason to adopt a position. 

Example: "My uncle Chet told me once that he used to get welfare even though he had a good job. Therefore, we need to get rid of the welfare system because it's being defrauded way too much."

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Appeal to Authority

Description: Reverse of the Ad Hominem argument. An argument which stakes its validity on the word of an supposed "authority". Appeals to authority endorses an idea based on who believes it. While it is more likely that a competent physician is more able to diagnose and treat illnesses than your Auntie Mae, there is still reason to bring a healthy dose of skepticism to the table. The fact that a person is in a position of authority (scholarly, politically or otherwise) does not automatically make their beliefs, and thus our premises, justifiable. Even experts disagree, base their work on inaccurate methods, or manipulate their findings in order to reach a certain conclusion. 

Example: "My teacher says that Oregon was the 2nd state in the Union, and she wouldn't lie."

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Appeal to the Extreme

Description: Variant of the Slippery Slope . Appeals to the Extreme attempt to bring highly emotional elements into an argument in an attempt to exaggerate it to the point of absurdity. The difference between Appeals to the Extreme and the Slippery Slope is that an appeal to the extreme does not necessary attempt to show a causal relationship between the first step and the last. 

Example: "Oh and if you're gonna repossess my car, why don't you just take my house, or how about one of my legs and an arm too!?!"

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Appeal to Ignorance, argumentum ad ignorantiam

Description: An attempt to use an opponent's inability to disprove your position as proof that your position is, indeed, true.

Example: "That new experimental drug must be working. There hasn't been a single patient who has come back and complained."

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Appeal to Nature, Naturalism

Description: An argument, often of an ethical nature, that supports its conclusion based an observation in nature. A general confusion in an "is/aught" problem.

Example: "Homosexuality must be OK; you see it all the time in wild monkeys." "Homosexuality isn't natural therefore it must be immoral.:

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Appeals to Popularity, ad populum, "playing to the gallery" 

Description: Variant of Appeal to Authority. In this fallacy, an arguer relies on premises "strengthened" by statistics or popularity.  Just because a large number of people believe a certain thing does not make it true.

Example: "Twice, a majority of people in the State of Oregon voted to legalize 'death with dignity'. Therefore, doctor assisted suicide is a good thing."

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Appeal to Tradition

Description: Variant of Appeal to Authority. In this fallacy, an arguer relies on premises "strengthened" by folklore. The truth-value of a premise is supposedly bolstered by the longevity of the belief. 

Example: "People have believed in the Bible for thousands of years. Therefore, the Bible is true."

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Appeal to Unknowable Statistics

Description: The insertion of unverifiable statistical information. 

Example: "The fact that the United States and Russia had nuclear weapons pointed at each other has prevented a dozen wars in Europe since the end of World War II."

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Begging the Question, petitio principii

Description: An argument which assumes some unproven or unstated "fact" which is designed to stump any objection. In question form, this is known as a Complex Question. 

Example: "Vegetarianism is much better for you because you cut out all meat from your diet." Or "Have you stopped beating your wife?"

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Description: Species of False Dilemma in which only two choices are given. This is usually expressed in black-and-white or all-or-nothing thinking. 

Example: "If you don't like America, you can always go back to the country you came from."

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Circular Reasoning

Description: Form of Begging the Question . Simply restating your premises as if they were your conclusion. Using part or all of a question in order to answer the question. 

Example: "The facts are true because they appear on Prof. Thomason's Web site.  Therefore, Prof. Thomason's Web site is true because it contains these facts."

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Description: An argument that is based on the fallacious assertion that, if certain members of a group express certain traits then, the whole group expresses those traits.

Example: "A person with a Jesus-fish on their car nearly ran me off the road; all Christians are hypocrites."

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Description: Opposite of Composition. Fallacious Division happens when we assume that characteristic found in a larger group are shared by a particular member of that group. 

Example: "Native Americans care about the environment, therefore Chief RedCorn must care about the environment."

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Emotional Appeals

Description: Appeals to Fear, Pity or Loyalty (among others). Emotions are not always irrelevant in making good decisions. Feelings of compassion and love, among others, can be quite relevant to a given issue. You may have good reason for setting out on a particular course of action on account of your compassion for a group of people. When one bases an entire argument on "scare-tactics", black-mail or an attempt to garner sympathy because of the current state of the arguer, then the argument fails. Because emotions, while powerful motivators, do not constitute logical grounds for believing one thing or another. 

Example: "If we don't do something now about the rampant expansion of the Republican agenda, this county is going to be a Third World nation in just a couple years." Or "If you love me, you'd go to the store and get me some ice cream."

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Description: An argument where a key word has its meaning slightly shifted during the course of laying out the premises. A term may have one meaning at the beginning of an argument, but has changed by the time it appears in the conclusion. 

Example: "Jesus loved prostitutes, and so do I. That's why I pay them well for their services."

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False Attribution, the Strawman

Description: An argument aimed at dismantling the inaccurately portrayed beliefs of another. Instead of refuting an accurate version of another person's argument, the arguer distorts the opposing views in order to make it easier to defeat. 

Example: "What Pat Robertson really means is that if we all don't join his church, we'll all burn in Hell."

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False Dilemma

Description: False Dilemmas use the process of elimination (disjunctive syllogism) in which the list of alternatives that are presented is incomplete. Often this list leaves out important alternatives or presents the list in misleading ways. In another form, a False Dilemma presents alternatives which we really do not have to choose between; that is, the choices are not mutually exclusive. 

Example: "People that protest the war in Iraq are either slaves of the U.N., Socialists or Al-Quida sympathizers." 

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Faulty Comparison

Description: An argument where the objects of comparison are in wildly different categories.  We may be asked to draw conclusions based on several categories which require--but are missing--substantial qualification. Obvious dissimilarities are ignored, which may involve Suppressed Evidence. The comparison could be figurative, in which it would be a Faulty Analogy. 

Example: "Automobile and steel industries, which have a lot of government regulation, are doing poorly, while electronics and computer industries, which do not have much regulation, are doing well. Therefore, government regulation is bad for industry."

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Genetic Fallacy

Description: Any argument that depends entirely on its origin to establish its conclusion, either positively or negatively.

Example: "Southerns can't be trusted because as it has been clearly show they are decended from Roundhead stock."

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Hasty Conclusion

Description: A Hasty Conclusion occurs when an argument presents relevant evidence but does not necessarily lead us to a credible thesis. Here, the arguer ignores the likelihood of their being alternative, and possibly better, explanations for the phenomenon in question. A Hasty Conclusion is an explanation for a collection of facts which the arguer, usually, insists is the only and true explanation. This can occur when the arguer either overestimates the plausibility of his or her theory or when he or she underestimates the plausibility of alternative explanations. Quite often, one can do both. 

Example: "Because of all the evidence--Easter Island statues, ancient stories of gods coming down from the 'heavens', astronomical observatories like Stonehenge, even the Bible (Ezekiel's wheels in the sky)--aliens from other planets must have been coming to Earth for a very long time."

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Hasty Generalization

Description: Occasionally disguised as an Appeal to Popularity . An argument which improperly generalizes from a sample. A Hasty Generalization may have been committed if the arguer bases a large part of the argument on a sample which is far too small to make reasonable generalizations from or may have based his or her argument on a biased sample. Both, of course, could be happening at the same time, as in the example. 

Example: "According to a recent study over 95% of college students are sexually active. Students attending a U.C. Berkeley course called 'Having Better Orgasms' filled out a questionnaire. Of the 30 males and 20 females, 95% said they were sexually active."

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Ignored Intention

Description: To ignore the original intention of an idea, policy or argument and then criticize it because it failed to meet expectations which it was never originally intended to address. 

Example: "That stupid Republican tax cut hasn't done anything to get my road paved!"

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Invincible Ignorance

Description: While not exactly a true fallacy, I have included this one here as something to watch for. Some people actually seem to take pride in refusing to listen to the arguments of the their intellectual opponents. Often faith, frustration or self-righteousness force people to tune out any possibility that they, themselves, might not be 100% right. 

Example: "I must be a good person; I won't even listen to those idiot pro-lifers."

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Irrelevant Reasons, ignoratio elenchi

Description: An argument is an example of Irrelevant Reason fallacy if the premises fails to support the conclusion. "Relevance" in this case referrers only to logical relevance, that is, the premises are not logically connected in such a way that it would be impossible to imagine a situation where the premises are true and the conclusion is false. Therefore, one way of demonstrating that an argument suffers from this fallacy is to show that it is possible to imagine a situation where the premises are true but the conclusion is false. 

Example: "All this environmentalism stuff is just silly. We can't make the Earth a Garden of Eden again. Besides, the Garden of Eden was such a boring place. Just look at how quickly Adam and Eve got tired of the place."

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Lack of Proportion

Description: An argument that suffers from Lack of Proportion is one which is based on questionable assessment of the significance of a particular premise or fact. Here, an arguer exaggerates the importance of a piece of evidence or simply overstates his or her case thereby discrediting his or her argument. 

Example: "Last year, we had two days of 100+ degree weather. This year, we had three. See? Global warming is totally changing the planet's ecosystem!"

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Poisoning the Well

Description: In this line of argument, the arguer attempts a pre-emptive Ad Hominen attack, which typically involves the labeling of an opposing position so that anyone who holds that position automatically brands themselves in a very negative way.

Example: "All those witch-hunting congressmen who are trying to investigate the intelligence used by the President to justify the war with Iraq are just traitors to this county."

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Description: Assuming what is familiar is the best. The failure to see that other people are likely to see the world differently than you. Provincialism is displayed when the arguer appears culturally or socially, politically or religiously myopic. 

Example: "Let them eat cake."

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Questionable Cause, post hoc ergo propter hoc, "after this, therefore because of this"

Description: Variant of the Hasty Conclusion fallacy. An argument which concludes that because an event of one kind is associated with an event of another kind, therefore the first event actually causes the second event. A person has posited a Questionable Cause when they claim that type A events necessarily causes type B events when there are other plausible explanations. Perhaps, the correlation was simply accidental, or perhaps the relationship is perhaps backwards (B causes A) or perhaps some third factor is involved which the arguer does not account for. 

Example: "A black cat crossed my path just before I tripped and broke my arm. Therefore, the black cat caused my broken arm."

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Red Herring

Description: Variant of Irrelevant Reasons. This fallacy is named after supposed tactics used by escaped convicts; in order to escape the pursuing bloodhounds, the convict would drag a stinking fish behind him and then toss it off to one side in the hope that the strong smell would divert the dogs from his trail. A Red Herring fallacy consists of introducing an emotionally charged statement, which while possibly true in itself, is designed to divert attention from a weak argument. 

Example: "Man, if we lived in China you'd be thrown in jail forever for talking that way about our leaders."

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Relative Privation

Description: An argument which attempts to show that one idea, action or phenomenon is the best choice, by comparing it with something even worse, or to make an idea, action or phenomenon appear worse by comparing it with something that is generally accepted to be good..

Example: "I used to lament having no shoes, until I met a man who had no feet."

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Slippery Slope

Description: An argument which fallaciously attempts to show that by taking step A, step Z will come to pass. Once you step onto the path started at point A, you are likely or even be compelled to continue to step Z. While there may be a natural casual link between each step, a fallacious argument of this type cautions us to avoid the first step without giving us proof that we won't be able to go back. 

Example: "If I make an exception for you, I'll have to make an exception for everyone."

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Suppressed Evidence

Description: While it is practically impossible to command every piece of evidence concerning a particular argument, it is possible to choose to ignore relevant information which could be of detriment to a particular position. An arguer might commit this fallacy when he or she attempts to manipulate his or her audience into accepting a Hasty Conclusion by omitting important facts or quoting sources out of context.  Here, the hope is that the argument's audience does not have possession of those important opposing facts. 

Example: "Auschwitz was used to house workers, therefore, its main purpose was to hold Germany's foreign work force."

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Description: A Tautology defines its terms in such a way that the statement cannot be disproved.  Therefore, Tautologies are not always fallacious.  They are only fallacious when the arguer simply restates his or her definition as a conclusion using different words. That is, the conclusion and the premise are identical. This is a statement which is logically true, but entirely uninformative. Where Circular Arguments deal with premises and conclusions which are interdependent, Tautologies usually deal with word or idea definitions. 

Example: "Paternal twins are identical. Therefore twins that look the same are paternal."

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Two Wrongs Make a Right, Tu Quoque

Description: Variant of the Ad Hominen fallacy. The Tu Quoque fallacy involves attempting to evade criticism by pointing out that your opponent is as bad as you are. 

Example: "Look who's talking!" Or "You hit me first!"

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