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A Short Catalog of Informal Fallacies

(The general grouping of the fallacies below, along with some of the examples, are from Patrick Hurley, A Concise Introduction to Logic, 4th ed., Wadsworth, 1982)

One general grouping of informal fallacies is as follows:

I. Fallacies of Relevance. The conclusion is irrelevant to the premises.

II. Fallacies of Weak Induction. The conclusion is not well-supported by the premises.

III. Fallacies of Presumption. The premises presume the truth of the conclusion or of some other important premise.

IV. Fallacies of Ambiguity. A term is used ambiguously or vaguely.

V. Fallacies of Grammatical Analogy. A property of a part is improperly applied to the whole, or vice versa. Such arguments are similar in appearance to grammatically similar, but good arguments.

I. Fallacies of Relevance

1. Appeal to force.

In this informal fallacy the arguer makes a claim, then threatens his opponent with harm if they donít accept that claim. The threat could be a physical threat, such as when one threatens another with violence if they donít accept the claim posed. The threat could also be a psychological one, such as threatening to make public some embarrassing information about the arguerís opponent. Some examples are as follows.

Harleys are the best motorcycles on the planet, and anyone in here who says otherwise is getting a bloody nose right now. (a physical threat)

I think I really deserve a raise. After all, Iíd hate to have to let your wife know youíve been cheating on her for the last five years. (a psychological threat) (Hurley 112)

2. Appeal to the people (ad populum)

In this fallacy the arguer uses common desires such as the need to be appreciated, to fit in, to be admired, etc. to persuade the listener to believe a conclusion. Such a fallacy may proceed directly, as when a speaker excites emotion in a crowd in order to take advantage of the common tendency of excited crowds to accept (often dubious) claims without much justification. An appeal to the people may also proceed indirectly, in the sense that the arguer appeals to oneís desired role as part of the crowd (rather than appealing to the crowd as a whole). Two examples of the indirect approach are given below.

2a. Bandwagon argument

In a bandwagon argument the arguer uses the common desire to fit in with the crowd in order to make his conclusion more likely to be accepted. For example,

I canít believe youíre not a Broncos fan. Everybody that lives around here is a Broncos fan.

2b. Appeal to Vanity

In this sort of appeal to the people the arguer uses the desire to be associated with someone or something that is admired or loved in order to get the listener to accept their claim. For example,

Come for dinner at the Ritz. The elite of New York City have dined here since 1920.

3. Argument against the person (ad hominem)

In an ad Hominem argument, instead of criticizing his opponentís position or argument the arguer just attacks his opponent himself. There are three kinds of ad hominem arguments: the ad hominem abusive, the ad hominem circumstantial, and the tu quoque "you too" argument.

3a. Ad hominem abusive

In this form of the ad hominem argument the arguer abuses his opponent verbally. For example,

Bill Gates has argued against further regulation of the software industry. But Bill Gates is just a billionaire geek whoís out to make more money and take over the world. His argument canít be a good one.

3b. Ad hominem circumstantial

In this form of the ad hominem argument the arguer points out some circumstances that affect his opponent in such a way that his argument or position gets discredited. Such arguments are very common; for example,

Bill Gates has argued against further regulation of the software industry. But remember that Bill Gates is the CEO of Microsoft, one of the largest software manufacturers. So, Gatesí argument canít be a good one.

In the above passage the arguer never considers Gatesí argument (whatever that might be), but instead just points out that Gates is the CEO of Microsoft. The arguer needs to be addressing Gatesí argument, not any interesting properties of Gates himself. The reason is that facts about Bill Gates himself have little or nothing to do with the strength or validity of Gatesí argument.

3c. Tu Quoque

In this form of the ad hominem argument an arguer makes his opponent appear hypocritical by pointing out something about the person heís arguing against. For example,

Mom, you canít tell me not to use drugs. After all, youíve admitted to me that when you were my age you used to smoke enough pot every night to get ten people stoned.

Notice that the arguer in the above passage merely points out something about his mother herself that makes her position on drug use appear hypocritical. Whether or not oneís mother used to use drugs (or even still does) has nothing to do with whatever her argument might be against the use of them.

4. Straw man (or straw person)

In this fallacy the arguer distorts his opponentís argument or position to make it appear weaker than it really is. The arguer then attacks the distorted version, making a conclusion against the original argument or position. For instance,

Jones has argued against allowing prayer in public schools. Obviously Jones is an atheist and advocates atheism. However, atheism was encouraged in the former Soviet Union as part of a campaign to suppress practice of all religions. We clearly don't want such a state to exist here, so Jonesí position canít be a good one (adapted from Hurley p. 119).

Jonesí position gets distorted into one that endorses atheism (which clearly isnít entailed by the claim that prayer in public schools is improper). The arguer then finds fault with atheism the distorted version of Jonesí real position), and concludes that Jonesí position is bad. Of course, attacking the distorted version of Jonesí position is irrelevant to the merit of Jonesí actual view.

5. Missing the point

When an arguer misses the point he puts forth a set of premises, but then draws a conclusion considerably different from one supported by those premises. Here is an example:

The crime rate in Milwaukee has been increasing at an alarming rate. Therefore, the state of Wisconsin should reinstate the death penalty (adapted from Hurley p. 120).

There may be a number of different conclusions one might draw given the premise concerning Milwaukeeís increase in the crime rate, but reinstatement of the death penalty is hardly supported by that premise.

6. Red herring

A red herring fallacy occurs when an arguer distracts the reader or listener with some claim that is irrelevant to the issue at hand. The arguer then makes a conclusion concerning the irrelevant issue, or draws no conclusion at all. For instance,

Environmentalists have complained about the dangers of nuclear power for quite some time. However, electricity is dangerous no matter how itís generated. In fact, people often forget that electricity is terribly dangerous. Many people get electrocuted each year because of such ignorance. Itís really too bad the government wonít do more to educate the public about the dangers of electricity (adapted from Hurley 121).

Here the arguer does nothing to address the issue of the dangers of nuclear power, but instead changes the subject to the danger of electricity. If thereís even an argument at all here, it certainly has nothing to do with the original issue.

II. Fallacies of Weak Induction

1. Appeal to authority

In an appeal to authority, the arguer uses the testimony of an expert as a reason to believe his conclusion. There are arguments of this kind that arenít fallacious, as when the expert in question is an expert on the issue the arguer is making a conclusion about. For instance, when someone claims they have cancer, and give as reason for their belief the prognosis of a doctor who is a specialist in cancer treatment, the argument isnít fallacious. However, if the expert isnít an expert on the topic in question, the argument often is fallacious. For instance,

CCU will probably go undefeated in football next year. My dentist is a smart person, and he thinks CCU will go undefeated next fall.

My dentist is surely a good judge of matters pertaining to dentistry. However, without some further evidence of his knowledge of the CCU football program (among other things) the argument given is a fallacious appeal to authority.

2. Hasty generalization

This fallacy occurs when an arguer draws an inductive inference on the basis of a sample size that is too small. For instance,

The last two times Iíve ordered a pint of Fat Tire itís turned out to be flat. Probably the next pint of Fat Tire I order will be flat.

It seems pretty clear that two instances of flat Fat Tire pints isnít enough evidence to warrant the inference to the next one being flat.

3. Slippery slope

A slippery slope fallacy occurs when an arguer makes a number of weak inductive inferences (often involving purported causal connections) to a conclusion that is undesirable. The arguer then concludes that the initial step in the chain of inferences shouldnít be accepted. For example,

In opposing the display of the Ten Commandments even in displays that teach students about law, history, and culture--no, not in displays that endorse Christianity--the ACLU battles against the teaching of any Christian history at all. If the school s must not teach about or show the Ten Commandments, then they must leave out all history of the origin of Christianity, the conversion of Rome, the Crusades, the Protestant Reformation and the Inquisition.

Do they really want to eradicate Western Civilization? Do they really want to remove history from the curriculum?  (from The Charlotte Observer, "Letters to the Editor", August 15, 1998)

In the letter there are a number of inductive inferences made concerning causal connections (such as between not teaching the Ten Commandments and not teaching all history regarding Christianity) on the way to the conclusion that if one accepts the ACL Uís initial position (opposing the display of the Ten Commandments), then the end result will be removing history from the curriculum of public schools. As such an end result seems undesirable it is tempting to reject the initial step that the ACLU proposes. However, as each of the inductive inferences in the argument are weak, itís ridiculous to suppose that the removal of history from the curriculum really will ultimately result from not allowing the Ten Commandments to be displayed.

III. Fallacies of Presumption

1. Begging the question

There are (at least) two main ways for an argument to beg the question: (1) arguing in a circle by presuming in the premises the truth of the conclusion, and (2) presuming the truth of an important but controversial premise. An example of the first sort of begging the question is as follows:

It says in the Bible that God exists. Since the Bible is Godís word, and God never speaks falsely, then everything in the Bible must be true. So, God must exist.

Itís pretty obvious that if the Bible is Godís word, then God exists (or at least did exist). However, since the argument also claims that the Bible really is Godís word, it presumes that God exists in order to purportedly prove that God exists. This is circular. Here is an example of the second sort of begging the question.

Murder is morally wrong. Therefore, abortion is morally wrong. (from Hurley p. 143)

The argument presumes the truth of a premise that isnít stated, namely that abortion is murder. As this premise is far from obvious, and the arguer doesnít even mention it (much less give it a defense), the argument begs the question.

2. Complex question

A complex question combines two or more distinct questions into a single one, thus presuming the truth of some claim. All of the following questions are complex questions.

Have you stopped using drugs?

Here no matter how one answers, one seems to admit to using drugs at some point. Thus the questioner makes an unwarranted presumption that whoever is answering the question is using drugs.

Are you still beating your wife?

Where did you hide the drugs you stole? (from Hurley p. 145)

A similar sort of move is made in the latter two complex questions.

3. False Dichotomy

A false dichotomy fallacy is made when the arguer presumes there are only two options available and rejects one option in favor of the other. However, it turns out that there are really more options available than the two given by the arguer. For instance, the familiar claim

If you donít love America then just get the hell out.

commits a false dichotomy. After all, there are other options than loving the system as it is and leaving the country. Such arguments can be more subtle, however. Consider the following argument that one might have made prior to the Senate's vote to remove President Clinton from office:

The U.S. Senate can either convict the president or not. If they donít convict him, then heíll be getting away with perjury and lying to the American people without being punished at all. So, they must do the right thing and convict him.

This argument might be improved with some more premises, but as stated it presumes that there are only two options with regard to the punishment of the president for his behavior. However, as it seems there are other options with regard to punishment (censure, his current punishment in the form of public humiliation, etc.) the argument as stated commits a false dichotomy fallacy.

IV. Fallacies of Ambiguity

1. Equivocation

An equivocation is made when a word is used in more than one meaning within the same argument without distinguishing between the different meanings. For example,

Some have argued that itís inappropriate for the press to investigate the private lives of public officials, movie stars, members of royal families, and other celebrities. However, the public has a right to know what is in the public interest, such as in cases of the governmentís raising taxes, its military expenditures, etc. The private lives of celebrities are also in the public interest, and since itís appropriate to make known what is in the public interest, it really is appropriate for the press to investigate the private lives of celebrities.

The phrase Ďpublic interestí is used equivocally in the above argument. In one premise it is used in the sense of what the public has a political interest in, and in another it is used in a sense of curiosity.

V. Fallacies of Grammatical Analogy

1. Composition

A composition fallacy occurs when an arguer inappropriately projects a property of the parts of something onto the whole. For example,

The CCU football team should be good next year. After all, everyone on the team is a good athlete, so the team as a whole should be good (adapted from Hurley p. 153).

A group of good athletes might not perform well together (among other things), so the inference is a weak one.

2. Division

A division fallacy is the reverse of a composition fallacy. A division fallacy occurs when an arguer inappropriately projects a property of the whole onto one or some of the parts. For example,
Salt is a nonpoisonous compound. Therefore, sodium and chlorine are nonpoisonous (from Hurley p. 155).

Yellowstone National Park is over 80 years old. Therefore, every tree in Yellowstone is over 80 years old (adapted from Hurley p. 156).


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