Fallacies - 1

Poisoning the Well

Etymology:

The phrase "poisoning the well" ultimately alludes to the medieval European myth that the black plague was caused by Jews poisoning town wells—a myth which was used as an excuse to persecute Jews.

The phrase was first used in its relevant sense by Cardinal John Henry Newman during a controversy with Charles Kingsley:

…[W]hat I insist upon here…is this unmanly attempt of his, in his concluding pages, to cut the ground from under my feet;—to poison by anticipation the public mind against me, John Henry Newman, and to infuse into the imaginations of my readers, suspicion and mistrust of every thing that I may say in reply to him. This I call poisoning the wells.

"I am henceforth in doubt and fear," he says, "as much as any honest man can be, concerning every word Dr. Newman may write. How can I tell that I shall not be the dupe of some cunning equivocation?" …

Well, I can only say, that, if his taunt is to take effect, I am but wasting my time in saying a word in answer to his foul calumnies… We all know how our imagination runs away with us, how suddenly and at what a pace;—the saying, "Caesar's wife should not be suspected," is an instance of what I mean. The habitual prejudice, the humour of the moment, is the turning-point which leads us to read a defence in a good sense or a bad. We interpret it by our antecedent impressions. The very same sentiments, according as our jealousy is or is not awake, or our aversion stimulated, are tokens of truth or of dissimulation and pretence. There is a story of a sane person being by mistake shut up in the wards of a Lunatic Asylum, and that, when he pleaded his cause to some strangers visiting the establishment, the only remark he elicited in answer was, "How naturally he talks! you would think he was in his senses." Controversies should be decided by the reason; is it legitimate warfare to appeal to the misgivings of the public mind and to its dislikings? Any how, if Mr. Kingsley is able thus to practise upon my readers, the more I succeed, the less will be my success. … The more triumphant are my statements, the more certain will be my defeat.

Source: John Henry Newman, Apologia Pro Vita Sua

Type: Argumentum ad Hominem

Example:

I wish it were possible for men to get really emotionally involved in this question [abortion]. It is really impossible for the man, for whom it is impossible to be in this situation, to really see it from the woman's point of view. That is why I am concerned that there are not more women in this House available to speak about this from the woman's point of view.

Source: House of Commons Debates of Canada, Volume 2, November 30, 1979, p. 1920

Analysis

Exposition:

To poison the well is to commit a pre-emptive ad hominem strike against an argumentative opponent. As with regular ad hominems, the well may be poisoned in either an abusive or circumstantial way. For instance:

1. "Only an ignoramus would disagree with fluoridating water." (Abusive)
2. "My opponent is a dentist, so of course he will oppose the fluoridating of water, since he will lose business." (Circumstantial)

Anyone bold enough to enter a debate which begins with a well-poisoning either steps into an insult, or an attack upon one's personal integrity. As with standard ad hominems, the debate is likely to cease to be about its nominal topic and become a debate about the arguer. However, what sets Poisoning the Well apart from the standard Ad Hominem is the fact that the poisoning is done before the opponent has a chance to make a case.

Exposure:

Poisoning the Well is not, strictly speaking, a logical fallacy since it is not a type of argument. Rather, it is a logical boobytrap set by the poisoner to tempt the unwary audience into committing an ad hominem fallacy. As with all forms of the ad hominem, one should keep in mind that an argument can and must stand or fall on its own, regardless of who makes it.

Analysis of the Example:

This is a common type of circumstantial poisoning of the well, which claims that men should either not make a judgment about abortion, or should keep it to themselves if they do. This illustrates the effect that poisoning the well tends to have, which is to forestall opposition in debate. It also shows the mistake underlying all poisoning of the well, since the sex of the arguer is irrelevant to the merits of the argument. No doubt one could always find a woman to advance the argument, whatever it is.

Sources:

• S. Morris Engel, With Good Reason: An Introduction to Informal Fallacies (Fifth Edition) (St. Martin's, 1994), pp. 206-209.
• Douglas N. Walton, Informal Fallacies: Towards a Theory of Argument Criticisms (John Benjamins, 1987), pp. 217-222.

Fallacies - 2

Alias: Post Hoc, Ergo Propter Hoc

Translation: After this, therefore because of this, Latin

Type: Non Causa Pro Causa

Forms
Event C happened immediately prior to event E. Therefore, C caused E.	Events of type C happen immediately prior to events of type E. Therefore, events of type C cause events of type E.
Examples
The only policy that effectively reduces public shootings is right-to-carry laws. Allowing citizens to carry concealed handguns reduces violent crime. In the 31 states that have passed right-to-carry laws since the mid-1980s, the number of multiple-victim public shootings and other violent crimes has dropped dramatically. Murders fell by 7.65%, rapes by 5.2%, aggravated assaults by 7%, and robberies by 3%.	…[E]vidence shows that even state and local handgun control laws work. For example, in 1974 Massachusetts passed the Bartley-Fox Law, which requires a special license to carry a handgun outside the home or business. The law is supported by a mandatory prison sentence. Studies by Glenn Pierce and William Bowers of Northeastern University documented that after the law was passed handgun homicides in Massachusetts fell 50% and the number of armed robberies dropped 35%.
Source: "The Media Campaign Against Gun Ownership", The Phyllis Schlafly Report, Vol. 33, No. 11, June 2000.	Source: "Fact Card", Handgun Control, Inc.

Analysis of the Examples

Counter-Example:

Roosters crow just before the sun rises.
Therefore, roosters crowing cause the sun to rise.

Exposition:

The Post Hoc Fallacy is committed whenever one reasons to a causal conclusion based solely on the supposed cause preceding its "effect". Of course, it is a necessary condition of causation that the cause precede the effect, but it is not a sufficient condition. Thus, post hoc evidence may suggest the hypothesis of a causal relationship, which then requires further testing, but it is never sufficient evidence on its own.

Exposure:

Post Hoc also manifests itself as a bias towards jumping to conclusions based upon coincidences. Superstition and magical thinking include Post Hoc thinking; for instance, when a sick person is treated by a witch doctor, or a faith healer, and becomes better afterward, superstitious people conclude that the spell or prayer was effective. Since most illnesses will go away on their own eventually, any treatment will seem effective by Post Hoc thinking. This is why it is so important to test proposed remedies carefully, rather than jumping to conclusions based upon anecdotal evidence.

Sibling Fallacy: Cum Hoc, Ergo Propter Hoc

Source:

T. Edward Damer, Attacking Faulty Reasoning: A Practical Guide to Fallacy-Free Arguments (Third Edition) (Wadsworth, 1995), pp. 131-132.

Resources:

• Julian Baggini, "Post Hoc Fallacies", Bad Moves.
• Robert Todd Carroll, "Post Hoc Fallacy", Skeptic's Dictionary.

Fallacy - 3

Weak Analogy

Alias:

• False Analogy
• Faulty Analogy
• Questionable Analogy

Type: Informal Fallacy

Form:

A is like B.
B has property P.
Therefore, A has property P.
(Where the analogy between A and B is weak.)

Example:

Efforts to ban chlordane assailed

WASHINGTON (AP)--The only exterminator in Congress told his colleagues Wednesday that it would be a short-sighted move to ban use of chlordane and related termiticides that cause cancer in laboratory animals.

Supporters of the bill, however, claimed that the Environmental Protection Agency was "dragging its feet" on a chemical that could cause 300,000 cancers in the American population in 70 years.

"This bill reminds me of legislation that ought to be introduced to outlaw automobiles" on the grounds that cars kill people, said Rep. Tom DeLay, R-Texas, who owns an exterminating business.

EPA banned use of the chemicals on crops in 1974, but permitted use against termites because the agency did not believe humans were exposed. Chlordane does not kill termites but rather drives them away.

Source: Associated Press, June 25th, 1987

Analysis

Exposition:

This is a very common fallacy, but "False Analogy", its common name, is very misleading. Analogies are neither true nor false, instead they come in degrees from near identity to extreme dissimilarity. Here are two important points about analogy:

1. No analogy is perfect, that is, there is always some difference between analogs. Otherwise, they would not be two analogous objects, but only one, and the relation would be one of identity, not analogy.
2. There is always some similarity between any two objects, no matter how different. For example, Lewis Carroll once posed the following nonsense riddle:

How is a raven like a writing desk?

The point of the riddle was that they're not; alike, that is. However, to Carroll's surprise, some of his readers came up with clever solutions to the supposedly unsolvable riddle, for instance:

Because Poe wrote on both.

Some arguments from analogy are based on analogies that are so weak that the argument is too weak for the purpose to which it is put. How strong an argument needs to be depends upon the context in which it occurs, and the use that it is intended to serve. Thus, in the absence of other evidence, and as a guide to further research, even a very weak analogical argument may be strong enough. Therefore, while the strength of an argument from analogy depends upon the strength of the analogy in its premisses, it is not solely determined by that strength.

Resources:

• Julian Baggini, "False Analogies", Bad Moves
• David Hackett Fischer, Historians' Fallacies: Toward a Logic of Historical Thought (Harper & Row, 1970), Chapter IX: "Fallacies of False Analogy".

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Analysis of the Example:

Representative DeLay attempts to argue against a bill banning chlordane by comparing it to a bill banning automobiles, but this analogy is very weak. Here are some of the relevant differences:

• Banning automobiles would be economically and socially disruptive in a way that banning a single pesticide would not.
• There are many alternative pesticides available to replace a banned one, but there are few modes of transportation available which could replace cars.
• Automobiles play a significant role in our society, whereas chlordane was used only to prevent termite damage to houses, which is of comparatively minor importance.

Fallacy - 4

Contradictory Premises (also known as a logical paradox): Establishing a premise in such a way that it contradicts another, earlier premise. For instance, "If God can do anything, he can make a stone so heavy that he can't lift it." The first premise establishes a deity that has the irresistible capacity to move other objects. The second premise establishes an immovable object impervious to any movement. If the first object capable of moving anything exists, by definition, the immovable object cannot exist, and vice-versa. The Liar Paradox The Liar Paradox is among the simplest of paradoxes. It can be traced back at least as far as Eubulides of Miletus, a fourth-century B.C. Greek philosopher. Eubulides’ version of the paradox is this: A man says that he is lying; is what he says true or false? However we answer this question, difficulties arise. If we suggest that what the man says is true, then we end in contradiction: if the man’s claim that he is lying is true, then he is lying, in which case what he says is false. If we suggest that what the man says is false, then we are no better off: if the man’s claim that he is lying is false, then he is not lying, in which case what he says is true. Both answers give rise to logical contradictions; it cannot be the case either that what the man says is true or that what the man says is false. The Liar Paradox is sometimes referred to as “Epimenides’ Paradox”, after the sixth-century B.C. Cretan who asserted that all Cretans are liars. The apostle Paul makes reference to Epimenides in Titus 1:12, writing, “It was one of them, their very own prophet who said, ‘Cretans are always liars, vicious brutes, lazy gluttons.’” Epimenides’ statement alone does not give rise to a paradox. What he says can’t be true, for if Cretans are always liars, and he is a Cretan, then he must be lying, in which case his statement is false. His statement could be false however; it could be that Epimenides is dishonest but that not all Cretans are liars. Paul, though, excludes this dissolution of the paradox, proceeding to say in the following verse, “This testimony is true.” This leaves Paul asserting that Epimenides truly said that he (and all other Cretans) are liars, which takes us back to Eubulides’ paradox above; Paul cannot be right.

Fallacy - 5

I. Argumentum ad Misericordiam (argument from pity or misery) the fallacy committed when pity or a related emotion such as sympathy or compassion is appealed to for the sake of getting a conclusion accepted.

1. Hence, assent or dissent to a statement or an argument is sought on the basis of an irrelevant appeal to pity. In other words, pity, or the related emotion is not the subject or the conclusion of the argument.

2. The informal structure of the ad misericordiam usually is something like this:

Person L argues statement p or argument A. L deserves pity because of circumstance y. Circumstance y is irrelevant to p or A. Statement p is true or argument A is good.

II. Some typical ad misericordiam fallacy examples follow.

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Georgia Banker Bert Lance should be excused from conflict of interest divestiture problems, former President Jimmy Carter asserted, because Lance's promise to sell his stock so that he can serve his government has depressed its market value.

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Oh, Officer, There's no reason to give me a traffic ticket for going too fast because I was just on my way to the hospital to see my wife who is in serious condition to tell her I just lost my job and the car will be repossessed.

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Members of Congress can surely see in their hearts that they need to vote in favor of passage of the Gun Bill allowing concealed weapons because their constituents who lobby for liberalizing firearms will be greatly saddened if they do not do so.

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Public Schools, K through 12, need to have much easier exams for students because teachers don't fully realize the extent of the emotional repercussions of the sorrow and depression of the many students who could score much better on easier exams.

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Richard P. Feynman, the Nobel Prize winning physicist, has been misunderstood almost all of his life. Since World War II, he came close twice to having a mental breakdown--first with the death of his wife and second with the explosion of the atomic bomb. I think that the Journal of Science should publish some of his later theoretical work out of our kind regard for his memory and from the interest of human concern for his difficult life.

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III. Related emotions include sympathy, love, regard, mercy, condolence, and compassion. Occasionally, an occurrence of a fallacy can be correctly analyzed as either the ad populum or the ad misericordiam fallacy since these fallacies overlap in their appeal.

IV. Non-fallacious uses of the ad misericordiam include arguments where the appeal to pity or a related emotion is the subject of the argument or is a pertinent or germane reason for acceptance of the conclusion.

1. Relief arguments are relevant to the problems raised by a disaster caused by a tidal wave and cholera outbreak in India.

2. If we have the choice of buying a newspaper from a blind news vendor, ad misericordiam considerations are not necessarily irrelevant. The essential question is whether the pity or compassion is relevant to the situation at hand and is being appealed to exclusively or excessively for the acceptance of the conclusion.

Fallacy - 6

Hasty Generalization

Alias: Converse Accident

Type: Unrepresentative Sample

Quote…

It's a story, say, about the New York City public schools. In the first paragraph a parent, apparently picked at random, testifies that they haven't improved. Readers are clearly expected to draw conclusions from this. But it isn't clear why the individual was picked; it isn't possible to determine whether she's representative; and there's no way of knowing whether she knows what she's talking about. Calling on the individual man or woman on the street to make conclusive judgments is beneath journalistic dignity. If polls involving hundreds of people carry a cautionary note indicating a margin of error of plus-or-minus five points, what kind of consumer warning should be glued to a reporter's ad hoc poll of three or four respondents?

…Unquote

Source: Daniel Okrent, "13 Things I Meant to Write About but Never Did", New York Times, 5/22/2005

Example:

Of course your columnist Michele Slatalla was joking when she wrote about needing to talk with her 58-year-old mother about going into a nursing home. While I admire Slatalla's concern for her parents, and agree that as one approaches 60 it is wise to make some long-term plans, I hardly think that 58 is the right age at which to talk about a retirement home unless there are some serious health concerns. In this era, when people are living to a healthy and ripe old age, Slatalla is jumping the gun. My 85-year-old mother power-walks two miles each day, drives her car (safely), climbs stairs, does crosswords, reads the daily paper and could probably beat Slatalla at almost anything.

Source: Nancy Edwards, "Letters to the Editor", Time, 6/26/00.

Exposition:

This is the fallacy of generalizing about a population based upon a sample which is too small to be representative. If the population is heterogeneous, then the sample needs to be large enough to represent the population's variability. With a completely homogeneous population, a sample of one is sufficiently large, so it is impossible to put an absolute lower limit on sample size. Rather, sample size depends directly upon the variability of the population: the more heterogeneous a population, the larger the sample required. For instance, people tend to be quite variable in their political opinions, so that public opinion polls need fairly large samples to be accurate.

Exposure:

Suppose that you are cooking a pot of spaghetti, and you fish out a single strand to test for doneness. If it is done, then you conclude that all of the spaghetti in the pot is done. Here, your sample is one strand of spaghetti, and the population is the entire potful of pasta. Have you committed the Fallacy of Hasty Generalization? No.

This is a familiar type of inference that most of us engage in whenever we cook something, for instance, when we taste a pot of soup to test whether it is sufficiently seasoned by tasting a single spoonful. We don't feel it necessary to test several spoonfuls, because we have every reason to believe that the spoonful we test is representative of the whole pot of soup. In the same way, a single strand of spaghetti can be representative of a whole pot of noodles.

The reason why these kinds of inference can work is because spaghetti is mass-produced, and every noodle from the same box is virtually identical to all the others. Moreover, if we put a whole boxful of spaghetti into a pot of boiling water, we can be pretty sure that all of them are being cooked for the same amount of time and at the same rate. It is in this way that we can know that the single noodle we test is a representative noodle, that is, it is like all the other noodles in the pot in terms of doneness.

How do such inferences go wrong? Let's return to the soup example: suppose that you season the soup by sprinkling spices onto its surface, but that you forget to stir the pot. Then, if you take your test spoonful from the top of the soup, without stirring, it is unlikely that it will be representative. Instead, you are likely to get much more of the spices in that spoonful than you would get from the bottom of the pot. If you fail to notice this, and conclude from your sample that the soup is sufficiently spicy, then you will have committed the Fallacy of Hasty Generalization. You will probably be disappointed later that the soup is not flavorful enough. This is why we stir a pot of soup after seasoning it, and before tasting it, so that the spices will be evenly distributed throughout the liquid, and a single spoonful will be representative of the entire pot.

When we are dealing with populations that are more variable than soup or spaghetti, we need to be not only careful how we take the sample, but we have to take a sample that is big enough to represent the variability of the population. If we are polling people's political views, then a sample of just one person is guaranteed to be misleading, no matter what opinions that person has. A hasty generalization occurs anytime the sample is not big enough to represent the population.

Source:

S. Morris Engel, With Good Reason: An Introduction to Informal Fallacies (Fifth Edition) (St. Martin's, 1994), pp. 137-140.

Resource:

Douglas Walton, "Rethinking the Fallacy of Hasty Generalization" A technical paper in PDF format.

Fallacy - 7

The Fallacy of Accident

Alias:

• A dicto simpliciter ad dictum secundum quid
• Dicto Simpliciter
• Sweeping Generalization

Type: Informal Fallacy

Form:

Xs are normally Ys.
A is an X. (Where A is abnormal.)
Therefore, A is a Y.

Example:

Birds normally can fly.
Tweety the Penguin is a bird.
Therefore, Tweety can fly.

Exposition:

The fallacy of Accident, one of Aristotle's thirteen fallacies, has been interpreted in various ways by subsequent logicians, perhaps because of the obscurity of The Philosopher's account. I will discuss only one of these interpretations here, due to its relation to recent developments in logic.

Consider the generalization "birds can fly" from the example. Now, it isn't true that all birds can fly, since there are flightless birds. "Some birds can fly" and "many birds can fly" are too weak. "Most birds can fly" is closer to what we mean, but in this case "birds can fly" is a "rule of thumb", and the fallacy of Accident is a fallacy involving reasoning with rules of thumb.

Common sense is full of rules of thumb which do not hold universally, but which hold "generally" or "as a general rule", as is sometimes said. Logicians have tended to ignore rules of thumb, probably because of their unscientific vagueness. However, in the past couple of decades, primarily due to research in artificial intelligence, which has shown the importance of such general rules for practical reasoning, there has been growing interest in so-called "default" or "defeasible" reasoning, of which rules of thumb are a part. As a consequence, there has also been a rebirth of interest in the fallacy of Accident.

The difference between rules of thumb and universal generalizations, is that the former have exceptions. For instance, flightless birds are exceptions to the rule of thumb that birds can fly. One might hope to represent this rule of thumb by the universal generalization "all non-flightless birds can fly", but even this is not correct, for flighted birds with broken wings cannot fly. One might still hope that some lengthy list of exceptions would do the trick. However, one can imagine many different scenarios in which a bird would not be able to fly: its feet are stuck in quicksand, all of the air around it has suddenly rushed into space, it has developed a phobia about flying, etc. One might then try to sum up this diversity of cases under the rubric of "untypical", or "abnormal", and say: "All typical or normal birds can fly". This is exactly what a rule of thumb is.

Rules of thumb differ from statistical generalizations such as "90% of birds can fly" in that there is no specific proportion of flighted to flightless birds that determines normality. The rule of thumb doesn't even necessarily imply that the majority of birds can fly, though it would be unusual if this didn't hold. We can imagine, for instance, that there might be so many penguins in Antarctica that the majority of birds would be flightless. However, our notion of normality applies to the familiar, everyday birds we see in our backyards, rather than "exotics" on distant continents. Clearly, then, rules of thumb are specific to a cultural and temporal context.

The fallacy of Accident occurs when one either attempts to apply such a rule of thumb to an obviously abnormal instance, or when one treats the rule itself as if it were an exceptionless universal generalization, rather than a defeasible rule of thumb.

Source:

S. Morris Engel, With Good Reason: An Introduction to Informal Fallacies (5th Edition), (St. Martin's, 1994).