This resource covers using logic within writing—logical vocabulary, logical fallacies, and other types of logos-based reasoning.
Contributors: Ryan Weber, Allen Brizee
Last Edited: 2018-01-10 09:57:31
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.
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 they are bad for the environment eventually the government will ban all cars, so we should not ban Hummers.
In this example, the author is equating banning Hummers with banning all cars, which is not the same thing.
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:
Even though it's only the first day, I can tell this is going to be a boring course.
In this example, the author is basing his evaluation of the entire course on only the first day, which is notoriously boring and full of housekeeping tasks for most courses. To make a fair and reasonable evaluation the author must attend not one but several classes, and possibly even examine the textbook, talk to the professor, or talk to others who have previously finished the course in order to have sufficient evidence to base a conclusion on.
Post hoc ergo propter hoc: This is a conclusion that assumes that if 'A' occurred after 'B' then 'B' must have caused 'A.' Example:
I drank bottled water and now I am sick, so the water must have made me sick.
In this example, the author assumes that if one event chronologically follows another the first event must have caused the second. But the illness could have been caused by the burrito the night before, a flu bug that had been working on the body for days, or a chemical spill across campus. There is no reason, without more evidence, to assume the water caused the person to be sick.
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.
In this example the author is equating the character of a car with the character of the people who built the car. However, the two are not inherently related.
Begging the Claim: The conclusion that the writer should prove is validated within the claim. Example:
Filthy and polluting coal should be banned.
Arguing that coal pollutes the earth and thus should be banned would be logical. But the very conclusion that should be proved, that coal causes enough pollution to warrant banning its use, is already assumed in the claim by referring to it as "filthy and polluting."
Circular Argument: This restates the argument rather than actually proving it. Example:
George Bush is a good communicator because he speaks effectively.
In this example, the conclusion that Bush is a "good communicator" and the evidence used to prove it "he speaks effectively" are basically the same idea. Specific evidence such as using everyday language, breaking down complex problems, or illustrating his points with humorous stories would be needed to prove either half of the sentence.
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.
In this example, the two choices are presented as the only options, yet the author ignores a range of choices in between such as developing cleaner technology, car-sharing systems for necessities and emergencies, or better community planning to discourage daily driving.
Ad hominem: This is an attack on the character of a person rather than his or her opinions or arguments. Example:
Green Peace's strategies aren't effective because they are all dirty, lazy hippies.
In this example, the author doesn't even name particular strategies Green Peace has suggested, much less evaluate those strategies on their merits. Instead, the author attacks the characters of the individuals in the group.
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. Often this is an appeal that presents what most people, or a group of people think, in order to persuade one to think the same way. Getting on the bandwagon is one such instance of an ad populum appeal.
If you were a true American you would support the rights of people to choose whatever vehicle they want.
In this example, the author equates being a "true American," a concept that people want to be associated with, particularly in a time of war, with allowing people to buy any vehicle they want even though there is no inherent connection between the two.
Red Herring: This is a diversionary tactic that avoids the key issues, often by avoiding opposing arguments rather than addressing them. Example:
The level of mercury in seafood may be unsafe, but what will fishers do to support their families?
In this example, the author switches the discussion away from the safety of the food and talks instead about an economic issue, the livelihood of those catching fish. While one issue may affect the other it does not mean we should ignore possible safety issues because of possible economic consequences to a few individuals.
Straw Man: This move oversimplifies an opponent's viewpoint and then attacks that hollow argument.
People who don't support the proposed state minimum wage increase hate the poor.
In this example, the author attributes the worst possible motive to an opponent's position. In reality, however, the opposition probably has more complex and sympathetic arguments to support their point. By not addressing those arguments, the author is not treating the opposition with respect or refuting their position.
Moral Equivalence: This fallacy compares minor misdeeds with major atrocities.
That parking attendant who gave me a ticket is as bad as Hitler.
In this example, the author is comparing the relatively harmless actions of a person doing their job with the horrific actions of Hitler. This comparison is unfair and inaccurate.
FALLACIES and PROPAGANDA
It is important to be able to evaluate what you read and hear. If you did not sort the credible from the incredible, the serious from the playful, the essential from the nonessential, the world would be full of conflicting and bewildering messages. Critical thinking enables you to distinguish between fact and opinion and distinguish sound from faulty reasoning.
One kind of faulty reasoning is a fallacy, a breakdown of logic. A fallacious argument is one that tries to argue from A to B, but because it contains hidden assumptions or factual irrelevancies, reaches an invalid conclusion.
Another kind of faulty reasoning results from substituting emotion for thought. Propaganda is an indirect message appealing primarily to emotion. It is aimed at forming opinions rather than increasing knowledge. Propaganda intends to persuade without offering a logical reason to adopt a particular view or take a particular action. While the word itself carries rather a negative connotation (implying intent to mislead or deceive) the techniques can be used in good causes as well—a Cancer Society fundraiser, for example. At least some propaganda techniques are used occasionally by non-profit organizations, advertisers, churches, news organizations, governments, and instructors.
For good or ill, makers of propaganda typically select facts most appropriate to their purpose and omit facts that do not help them achieve that purpose. Because some propaganda uses facts (albeit selectively), it can look like a reasoned argument. But because it fails to make a logical case, propaganda is often fallacious as well as emotional.
Fallacies and propaganda devices are slippery by nature; they overlap, are often used in combination, and do not always fit neatly into one category or another. Following are examples.
Ad Hominem Fallacy
An ad hominem fallacy redirects the discussion of an issue to a discussion of one of the subjects—to his or her personal failings, inconsistency, or bias. For example, in a discussion of the pros and cons of privatizing Social Security, it would be an ad hominem attack simply to declare your opponent a parasite feeding on the lifeblood of the working class. Similarly, you would be guilty of an ad hominem attack if you exclaimed, “How can you claim to be a born-again Christian?” (pointing out an inconsistency of position) or “Of course you would say that—you’re a Libertarian!” (pointing out personal bias). None of these response addresses the actual pros and cons of the proposal to privatize Social Security.
A preemptive ad hominem attack, launched before the discussion fairly begins, is called “Poisoning the Well” (below).
Ad Nauseum Fallacy
Hitler’s Propaganda Minister, Joseph Goebbels, said that if only you repeat something often enough, people will come to believe it. Ad nauseum repetition is the stuff urban legends are made of. Less harmless than urban legends is the indoctrination (“brainwashing”) of cult groups, which aims to create belief by aiming sheer, ad nauseum repetition relentlessly at an exhausted subject.
Fallacy Based on Appeal to Belief, Common Practice, or Expertise
An appeal to belief suggests that, since most reasonable people (of your sort) believe something, you should believe it, too. “Educators fear that vouchers will undermine funding for public schools.” Educators in particular might be inclined to conclude that this fear is universal among educators, and identify with the belief because they identify with the group.
Appeals to common practice suggest that most everyone does it, and furthermore that it is therefore okay; “Nobody in California comes to a full stop. That’s why they call it ‘the California Stop.’”
An appeal to expertise dares you to pit your own ignorance against experts making a value claim (a Grammy award-winning country singer publicly endorses a political candidate, for example). Now, specialists agreeing on objective claims about matters within their field of expertise are reasonably to be believed, but specialists making value judgments outside their field might not. (For more, see the TIP Sheet “Objective and Subjective Claims.”)
Phrases like the following might signal an appeal to belief, expertise, or common practice:
“Any reasonable person would…”
“It’s obvious that…”
Fallacy Based on Appeal to Indignation or Anger
The problem with the appeal to indignation or anger is that anger is a poor substitute for reasoning. On the contrary, anger clouds thinking. Certainly anger is sometimes justified, when it follows an argument that gives me grounds for anger, but anger is not the way to reach that conclusion. And anyway, sometimes we are angry for irrational reasons.
For example: “The governor is cutting education funds!” may cause a reaction of anger, followed by the conclusion, “The governor is a dolt and a fascist!” (see “Name-Calling,” below). Anger short-circuits the reasoning process, whereby we might have examined the figures and learned (much to our surprise) that education funding is up from last year—just not up as much as originally hoped.
Fallacy Based on Appeal to Pity
Who has not seen the heartbreaking pictures of starving orphans with the request for donations to ease their plight? A valid appeal to pity has a direct link between the object of pity (starving children) and the desired action (the money that can help feed them).
Appeal to pity becomes a fallacy when there is no logical link between the arousal of pity and the desired action: “Please give me a break, Professor. If I don’t pass this class I’ll lose my financial aid.” Whether this student is qualified to pass the class depends on the quality and quantity of work completed, not on financial need. There is no relevant connection between the student’s need on the one hand, and the quality of work she has (or has not) performed on the other.
Fallacy Based on Appeal to Popularity or Bandwagon
Appeal to popularity exploits the human desire to belong to a group. While there is nothing wrong with belonging to a group, some decisions are not group decisions, should be made without taking a head count, and should be held to even if they are unpopular. For example, my softball team’s consensus should probably not be the determining factor in my decision to take a cut in pay in return for more flexibility in my working hours. My softball team’s disapproval (they think I should go for the higher salary) should be irrelevant.
“Jumping on the bandwagon” is supporting a cause or position merely because it appears to be popular or winning. Politicians who waver from one position to another are sometimes trying to protect their jobs by appealing to the greatest number of voters based on changing poll information. Of course, it is reasonable sometimes to change one’s mind; it is just usually preferable to base the change on reason.
Fallacy Based on Appeal to Ridicule
Sarcasm is always hostile. Ridicule, sarcasm, and the “horse laugh” are the persuasion techniques of bullies. Appeal to ridicule tries to convince you to accept an argument in order to avoid becoming the butt of the joke. The laugh might be at the person (see “Ad Hominem,” above) or at his position (see “Straw Man,” below). Whether it is blatant or subtle, ridicule essentially denies discussion.
Apple Polishing Fallacy
Apple polishing is connecting compliments to unrelated issues. It urges someone to accept a claim in the afterglow of pleasure at the compliment. “You are by far the best math teacher I’ve ever had. You made me love math! I think I may change my major to math. I want to be just like you. Oh—I haven’t finished that chapter review; you don’t mind if I hand it in late?”
Fallacy Based on Begging the Question
Begging the question is a type of circular reasoning that presents as a true premise an assertion that actually requires its own proof. This leads to a “conclusion” that has already been pre-supposed or implied. For example, a student complains bitterly that he failed the English composition exit exam. “The test is bogus! I’ve taken it twice now, and they won’t pass me!” The student concludes that the test is bogus. His implied premise is that his essay is, in fact, good enough to pass. But whether his essay is good enough to pass is, itself, the question. Asserting that it is (or implying that it is) is not sufficient to prove that it is. (Application of the test rubric, by trained test scorers—twice—would appear to conclude that it is not.)
Distribution Fallacies: Composition and Division
Distribution fallacies arise two ways: In the composition fallacy, I know the characteristics of the whole, and (wrongly) attribute those characteristics to each of its parts. Stereotyping of individuals may result from a composition fallacy. Suppose I have read statistics that attribute very strong business ambition to a certain demographic group. I then attribute business ambition to each person of that group, without respect for individual variations (See also “Hasty Generalization,” below).
In its converse, the division fallacy, I know the characteristics of an individual or part, and (wrongly) attribute those characteristics to the whole. However, the parts are not necessarily representative of the whole. Broad stereotyping of a group may result from the division fallacy. Suppose I have become acquainted with a man from Taiwan who is an extremely talented electrical engineer. I mistakenly conclude that all Taiwanese, as a group, are amazing electrical engineers.
False Dilemma Fallacy
The false dilemma fallacy limits responses to those which serve the ends of its user (“Yes or no?”), implicitly denying the middle ground (“Maybe…”) or any qualified response (“Yes, but…”) . In a discussion on illegal immigration from Mexico to the U.S., for example, there is a vast middle ground of discussion between the extremes of building a very high fence on the one hand, and allowing uncontrolled immigration with its associated high social costs on the other. To suggest that a discussion on immigration is simply a choice between the two extremes is a false dilemma.
Political surveys frequently pose questions positing false dilemmas, using loaded questions that are worded in such a way that the desired attitude is suggested in the question. The responder is thus “steered” toward the desired response.
Guilt by Association Fallacy
The guilt by association fallacy muddles the process of fairly evaluating an idea, person, or group by interjecting irrelevant and misleading negative material. Think of it as a kind of red herring (below). This fallacy tries to connect ideas or persons to something unsavory or untrustworthy in order to discredit them. Take, for example, this claim made by an individual running against the incumbent for the office of sheriff: “Our sheriff has breakfast every single week with the head of a white supremacist group.” The fact that this weekly breakfast is attended by thirty-five local businessmen, including the head of the white supremacist group, is selectively omitted here (See also “Stacking the Deck, below). Be on guard when you see phrases like these:
“has ties to…”
“is the parent company/subsidiary of…”
“was a member of…”
Hasty Generalization Fallacy
A hasty generalization draws an unwarranted conclusion from insufficient evidence (see also “Distribution fallacies,” above). It often happens when the sample is too small to support the conclusion. For example, data compiled from 1,000 households, all in Nebraska, would probably be insufficient to accurately predict the outcome of a national election. Hasty generalization occurs, as well, when the sample is too biased to support the conclusion: Ten million households, selected from all fifty states, but all of them Libertarian (or Democrat, or Republican), may also be insufficient to predict the result of a national election.
Another kind of hasty generalization occurs as the result of misleading vividness. For example, a man in Tonga who watched many American daytime dramas (“soap operas”) might conclude that people in the U.S. were more materially prosperous, more well-dressed, more vicious, more self-centered, and more immodest than most of them are.
Name-calling is not so much a fallacy (see “Ad hominem,” above) as it is a propaganda technique, a crude attempt to make mud stick. It does not pretend to thoughtfully address issues or prove anything.
“The femi-Nazis want to eliminate gender.”
“We don’t need any more right-wing theocrats (or leftist, activist judges) on the bench.”
“This administration is a bunch of lying, neo-Fascist colonialists (or liberal, atheistic social engineers).”
“America is the Great Satan.”
Negative Proof Fallacy or Argument from Ignorance
The negative proof fallacy declares that, because no evidence has been produced, that therefore none exists. For example, a theist might declare, “You atheists cannot prove God does not exist, therefore God exists.” On the other hand, the atheist declares, “You deists cannot prove that God exists, therefore God does not exist.” First of all, the lack of proof one way or the other does nothing to prove or disprove God’s existence; the deist and the atheist may just as well make simple assertions: “God exists,” and “God does not exit.” Second, the general rule is that the person who asserts something has the burden of proof to provide evidence to support that something. It is not sufficient to make the assertion and then shift the burden of proof to the listener to prove you wrong.
Poisoning the Well Fallacy
Poisoning the well is an ad hominem attack (see “Ad hominem,” above) on a person’s integrity or intelligence that takes place before the merits of a case can be considered. It redirects a discussion to the faults of one of the parties. “Of course she will oppose the tort reform bill—she’s a lawyer, isn’t she?” The speaker suggests that something (greed? law school?) has corrupted the lawyer’s thinking to a degree that she cannot evaluate the tort reform bill on its own merits. Now the discussion is no longer about the merits of the tort reform bill at all, but about the personal qualities and motives of the other party.
Questionable Cause Fallacy
A questionable cause fallacy is the result of incorrectly identifying the causes of events either by oversimplifying or by mistaking a statistical correlation for a cause. Oversimplifying occurs when complex events with many contributing causes are attributed to a single cause: “School shootings happen because bullying makes students ‘snap.’” Since at least some bullied students do not shoot their classmates, this would appear to be oversimplified. Mistaking correlation for cause can happen when unrelated events occur together, either by chance or because they are actually both results of yet another cause. For example, does eating more ice cream in the summer cause an increase in crime rates? The rates for ice cream eating and violent crime both rise each summer. However, the statistical correlation notwithstanding, eating ice cream does not cause violent crime to increase. Rather, ice cream eating and crime may rise together as a result of a common cause—hot weather.
There may be an evolutionary advantage to discerning cause and effect; we’re hard-wired to look for causes, even if wrongheadedly. The tendency for humans to “see” a pattern where none exists is called the clustering illusion, demonstrated by the Texas sharpshooter fallacy: The Texas sharpshooter fires a hundred shots randomly into the side of barn. He then paints a target around the thickest cluster of holes. He has taken statistically non-significant, random data and attributed to it a common cause. The perennial attempts to find meaningful, hidden codes in the works of Shakespeare or the Bible (or the works of Leonardo da Vinci) illustrate the clustering illusion.
Fallacy Based on Scare Tactics or Appeal to Fear
Scare tactics create appeal from emotion. For example, the following appeal to fear requires me to accept a certain standard of “businesslike” attitude and behavior on grounds of fear:
This company expects a high level of commitment; be here in the office finishing the proposal through the weekend. Don’t forget your employee review is Monday.
Whether we can agree on what an acceptably “high level of commitment” is will have to wait for another time, since my immediate problem is avoiding the implied threat of a poor employee review. A warning differs from scare tactics because a warning is relevant to the issue. For example, it would be foolish to ignore the following warning:
No late research papers will be accepted; you cannot pass the class without a passing grade on this paper.
Slippery Slope Fallacy
Slippery slope arguments conclude that, if an eventual, logical result of an action or position is bad, then the original action or position must be bad. It is characteristic of a slippery slope argument that the final badness arrives in increments; thus, even though the badness could have been foreseen and may even have been inevitable, most of us are taken by surprise. Slippery slope arguments are common in social change issues.
A slippery slope argument is not necessarily a fallacy. It becomes a fallacy when the chain of cause and effect breaks down. If I cannot show you the reason why a causes b, and b causes c, and c causes d, my argument is fallacious. Typically, the (fallacious) chain of “logical” intermediate events becomes improbably long and unlikely, exponentially increasing the unlikelihood of the final result.
Often a historical precedent is cited as evidence that the chain of increasingly bad effects will occur. For example, there exist several historical precedents for the confiscation of guns by oppressive governments: in both Marxist and Nazi states, for example, the government confiscated the guns of citizens based on the registration records of those guns. Gun aficionados in the U.S. argue that gun registration anywhere will inevitably lead to confiscation of guns by the government. However, as a simple matter of logic, a historical precedent alone does not make those results necessary (or even probable) in every case. Gun registration opponents could avoid the slippery slope fallacy if they could show the reason why registration leads inevitably to confiscation. Or, if gun registration opponents could demonstrate that the principle that favors registration of guns is the same principle that would allow confiscation of guns, the fallacy may be avoided.
Smokescreen or Red Herring Fallacy
The smokescreen fallacy responds to a challenge by bringing up another topic. Smokescreen or red herring fallacies mislead with irrelevant (though possibly related) facts:
“We know we need to make cuts in the state budget. But do you really think we should cut funds for elementary physical education programs?”
“Well, we have to cut something. This governor has turned a million-dollar surplus into a billion-dollar shortfall. And what’s up with that shady software deal he made?”
Why red herring? A herring (a salt-cured fish) has a very strong odor; drag one across the trail of an animal and tracking dogs will abandon the animal’s scent for the herring’s. (A satirical fictitious example is the “Chewbacca Defense,” first used on the television show South Park in 1998, in which a lawyer convinces a jury to convict (and later to acquit) by misleading them with irrelevant facts about Wookies; for more information, see http://en.wikipedia.org/wiki/Chewbacca_Defense.)
Stacking the Deck Fallacy
Stacking the deck is a fallacy of omitting evidence that does not support your position. Like the card shark who “stacks” the cards before dealing to favor his own hand, a person who stacks the deck of an argument is cheating. All the cards favor him, because he has arranged them so. On the contrary, honest treatment of a discussable issue should evaluate evidence both for and against one’s own position. Stacking the deck can achieve short term wins against the unwary, but eventually a card stacker’s credibility will suffer.
For example, look again at the claim made above (see “Guilt by Association”) by the person running against an incumbent for the office of sheriff: “Our sheriff has breakfast every single week with the head of a white supremacist group.” This assertion might win the challenger some votes; note that the incumbent cannot truthfully deny it and independent investigation would confirm it. However, the challenger has selectively omitted the fact that this weekly breakfast is attended by thirty-five local businessmen, including the head of the white supremacist group. Should someone effectively expose the cheat before the election, the challenger will appear in an unfavorable light.
Straw Man Fallacy
If I take a complex position and oversimplify it in order to more easily overcome it, I am guilty of the straw man fallacy. In a sense, a straw man fallacy is a type of red herring (above), in that it misleads by misrepresenting the opponent’s position. Complex ideas about family planning are misrepresented below:
“The nuns taught us family planning was a sin. We would have to keep having babies because babies were a blessing, no matter how many of them already were in the house.”
The speaker may go on to demonstrate how unnatural and medieval such ideas are, defeating the straw man he himself has created. Instead of defeating his opponent’s best argument, he takes a weak argument, falsifies it, and then “overcomes” it. Political parties often demonize each other, painting extreme caricatures of each other’s actual, more thoughtful, positions in order to argue more easily (in marketable sound-bites) against them.
The straw man fallacy works best if the characterization closely resembles the real one; that is, if I choose to misrepresent your position, I should not be too obvious about it.
Subjectivist or Relativist Fallacy
The subjectivist or relativist fallacy turns all disagreements into matters of opinion by claiming that what is true and what is false are different for different people. In matters of fact, such a claim cannot be made without making nonsense. In matters of opinion, however, there exists no single standard to prove one or another claim conclusively true or false. The rightness or wrongness of either opinion might very well depend on where you stand. But even for matters of opinion, if there is no “truth,” then any opinion seems as good as any another and all opinions seem essentially groundless and equally meaningless. On the contrary, it is a virtue of a “good” opinion that it has a basis in evidence and logic. For more, see the TIP Sheets “Objective and Subjective Claims” and “Deductive, Inductive, and Abductive Reasoning.”
A subjectivist fallacy on a factual matter puts an end to rational discussion:
A: “The earth is roughly spherical, and goes once around the sun in about 365 days.
B: “That may be true for you, but it’s not true for me. And I have a right to my opinion.”
But a subjectivist claim even on a subjective matter (“It may be wrong for you, but it’s right for me!”) makes further discussion difficult by eliminating the common ground for discussion.
Fallacy Based on Transfer
Transfer is an emotional appeal that associates something or someone known (and therefore implied “good”) with a product, idea, or candidate. Celebrity endorsements are an example. Well-known objects and images can be used the same way, evoking an emotional response that sponsors hope will transfer to their cause. For example, images of Arlington National Cemetery might be used to help raise money for veterans’ groups. The image of Mount Everest is often used to help sell outdoor products (though relatively few of the products’ users will ever actually attempt to climb Everest).
Wishful Thinking Fallacy
Wishful thinking is choosing to believe something is true because we really, really want it to be true. We usually perpetrate wishful think on ourselves, but it also underlies many “positive thinking” philosophies: to believe in your dream is to make it come true. Though wishful (positive) thinking followed by action may help me achieve my goals, wishful thinking alone achieves nothing. Wishful thinking promotes comfort, but it does not promote reasoning.
2005 by Rosemary McKeever