FALLACIES

FALLACIES OF INSUFFICIENT EVIDENCE / WEAK INDUCTION

Last Updated: 4/7/09

Notes © Dwayne Mulder

WHAT IS A FALLACY?

• “Fallacy” means a common, frequently occurring, error in reasoning. Not every error in reasoning is a fallacy.

• “Fallacy” does not mean “false.” A bad argument, a fallacy (logical evaluation), can contain any combination of true and false statements (factual evaluation), including all true statements.

• Cognitive fallacies resemble perceptual illusions (see more here) in at least three ways:

-They are both “robust,” meaning that they often persist even after you have identified them. For a really robust perceptual illusion, check out the McGurk Effect!! (plus, just for fun, here’s a great site for 3-D stereo photos from around the world.)

-They are both the natural & predictable by-product of generally powerful, accurate systems. They are expected “glitches in the system.”

-We guard against them mainly by recognizing the contexts in which they are likely to occur

muller shepard-tables-illusion

The famous Müller-Lyer illusion is on the left above. The vertical line on the left appears shorter but is the same length as the line on the right. The illusion persists even after it has been explained to you. On the right is a more powerful illusion. The surfaces of the two tables are exactly the same shape and size. Measure them!

INDUCTIVE RELEVANCE:

• Relevance, Positive – A statement (A) is positively relevant to another statement (B) if and only if the truth of A increases the probability of B. For example, “Scott is a heavy smoker” (A) increases the probability of “Scott will get lung cancer” (B). Although (A) does not give high probability to (B), it increases the likelihood of (B).

• Relevance, Negative – (A) is negatively relevant to (B) if and only if (A) decreases the probability of (B). For example, “Scott is a heavy smoker” decreases the probability of “Scott will live to be 75.”

• Logical Irrelevance – (A) is logically irrelevant to (B) if and only if (A) has no influence on the probability of (B). For example, “Scott is a heavy smoker” does not affect the probability of “Scott’s birthday is in June.”

“The coin has come up heads the last five tosses” has no effect on the probability of, “Therefore, it will probably come up tails in the next toss.” It is logically irrelevant. Thinking it is relevant is called the Gambler’s Fallacy. People guilty of this fallacy say things like, “Tails is due” or “The law of averages has to kick in” or “What are the odds of getting six heads in a row?!” People routinely make too much of clusters of outcomes even in random events. Listen here.

• Inductive relevance or irrelevance, like inductive strength or weakness, is objective. It is a fact in the objective world, for example, that Scott’s being a heavy smoker increases his risk of getting lung cancer.

WHAT IS A FALLACY? (TOP)

FALLACIES OF INSUFFICIENT EVIDENCE / WEAK INDUCTION

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

FALLACIES OF (IR)RELEVANCE:

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

FALLACY:

• Ad Hominem – Personal attack (character attack)

–Rejecting an argument or expert testimony based on an irrelevant attack of the arguer’s character (disputing an alleged expert’s qualifications is relevant)

• Ad Hominem – Attacking the motive

–Rejecting an argument based on irrelevant criticism of the arguer’s motivation for giving the argument (usually charging the argument is motivated by self-interest). (Sometimes you see the reverse – a person uncritically accepting an argument just because it goes against the narrow self-interest of the person giving it. I don’t know of a good name for that one.)

• Ad Hominem – Look who’s talking

–Rejecting an argument or expert testimony because the arguer is being hypocritical (usually through practical inconsistency). Of course, if the argument itself contains a logical inconsistency, that is relevant to criticizing the argument.

CORRECT ARGUMENTATION:

•We should assess an argument on its own merits, rather than on where it came from.

•When assessing someone’s Testimony, given in a Report (review “Reports” as non-arguments in “Basic Concepts”):

–Character, motivation, consistency are relevant to assessing testimony.

–When assessing testimony, we should always ask whether the person giving the report is in a position to know what they claim to know.

–Logical inconsistency or practical inconsistency legitimately undermine someone’s testimony: If they say both “A” and “not-A,” you can’t rationally accept either claim based only on their testimony, and if they don’t “practice what they preach,” it might be because they don’t really believe what they are telling you.

•EXPERT TESTIMONY should be evaluated based on the qualifications of the expert, not on the authority’s personal character. We can sometimes question the motive, even of experts in some cases, but must do so cautiously. Logical inconsistency always undermines testimony, even of experts. Practical inconsistency generally is not relevant to assessing expert testimony. (Consider the case of an M.D. who advises you to eat a healthy diet and get more exercise even though he is overweight, eats junk food, and gets no exercise. The M.D. still has very good advise.) In some cases, however, a failure to “practice what they preach” can raise relevant concerns about the experts’ honesty or their expertise. (See also Inappropriate Appeal to Authority)

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

FALLACY:

•Two wrongs make a right

–Trying to justify a wrongful act by irrelevantly pointing to someone else’s equally wrong act

–This is sometimes a “twisted” argument by analogy, arguing that, since my wrong act is analogous to someone else’s wrong act, and they are not being punished, I should not be punished.

CORRECT ARGUMENTATION:

•Arguing that similar wrong acts should be handled in similar ways; arguing by analogy that they should be equally punished.

•The truth is that two wrongs don’t make a right (but three rights make a left)

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

FALLACY:

•Scare Tactics (irrelevant or manipulative appeal to fear, intimidation)

–Threatening harm (usually implicitly) for not accepting the arguer’s conclusion, or

–Appealing to irrelevant or exaggerated fears in your audience to support a conclusion. For example, “Your home might be struck by a meteor. Therefore you should buy our new and improved home meteor shield.”

–The influence that the expressions of a person in power have on the thinking of someone under them. Depends on power inequalities.

CORRECT ARGUMENTATION:

•Appealing to relevant, appropriate fears. (It’s all about relevance.) For example, “You should have an earthquake kit, because the risk of a major earthquake hear is significant.”

•Appealing to the “Force of Reason.” This force is relevant, and not scary. –Best used among equals

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

FALLACY:

•Appeal to Pity (irrelevant or manipulative appeal to emotion other than fear)

–Trying to support a conclusion with irrelevant emotional appeals (any emotion other than fear, not just pity)

CORRECT ARGUMENTATION:

•Proper, relevant appeals to emotion are logical. (It’s all about relevance.)

•Appeals for charity, for example, are generally relevant emotional appeals.

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

FALLACY:

•Bandwagon Argument / Appeal to the People

–Appealing to people’s desire to fit in, or be popular, to support your conclusion

–Peer pressure, conformism

–“groupthink”

–Appealing to common, widespread, belief

–“You should believe it because ‘everybody’ does.”

–Common expressions include, “Get with the program,” “Get on board” and “Fall in line/Toe the line”

–Widespread beliefs, such as urban legends, often have no basis (check out your favorite urban legends at www.snopes.com) See, for example, these widely believed medical myths.

–Internet “Echo Chambers” = “groupthink”

–Mindlessly following fashion is the bandwagon fallacy.

CORRECT ARGUMENTATION:

•Appealing to Common Knowledge, where “everybody” also knows the supporting evidence.

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

FALLACY:

•Straw man

–Misrepresenting, caricaturing, an opponent’s position (thesis) or argument

CORRECT ARGUMENTATION:

•You should face up squarely to opposing positions and arguments, i.e., any negatively relevant evidence

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

FALLACY:

•Red herring

–Diverting your audience onto a logically irrelevant point

–This generally catches fallacies of relevance that don’t fit into any more specific category

CORRECT ARGUMENTATION:

•Stay on the main topic

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

FALLACY:

•Begging the Question / Circular Reasoning

–Stating or assuming in your premises what you set out to prove

–Assuming in the argument anything that needs to be argued

–(See examples at the bottom of this web page, since the textbook doesn’t provide many good examples.)

CORRECT ARGUMENTATION:

•It’s deductively valid, but always useless

WHAT IS A FALLACY? (TOP)

FALLACIES OF INSUFFICIENT EVIDENCE / WEAK INDUCTION

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

FALLACIES OF INSUFFICIENT EVIDENCE / WEAK INDUCTION:

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

FALLACY:

•Inappropriate Appeal to Authority

–Using a witness, authority, or expert testimony that is not strong or relevant to the argument’s topic

–Using a source that is biased

–Includes appeal to claims that are controversial among the qualified experts

–Most often involves appealing to good authorities outside of their area of expertise (e.g., citing a famous scientist to support a claim about the best artist of the 20^th century). For example, Linus Pauling, who won two Nobel Prizes (one for chemistry, the other for peace), had no expertise in medicine. Yet millions of people believed his claims, which have never been supported in several controlled experiments, that large doses of vitamin C can decrease the incidence of the common cold and possibly even fight cancer. See UnSpun page 120

CORRECT ARGUMENTATION:

•Appropriate Appeal to Qualified Authority = Good Research, Relevant to your thesis

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

FALLACY:

•Appeal to Ignorance / Misplaced Burden of Proof

–“Accept my thesis because it has not been disproved”

–Any incorrectly identification of the Burden of Proof

CORRECT ARGUMENTATION:

•Appeal to Systematic Testing = it has not been disproved despite good efforts

–Requires correctly locating where the Burden of Proof lies

–Special legal case: “Presumed innocent until proven guilty” – burden of proof always on the prosecution

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

FALLACY:

•False Alternatives / The Either-or Fallacy

–Deductively valid: Argument by Elimination

–A fallacy when there are obviously more options

–Any clear oversimplification of an issue

CORRECT ARGUMENTATION:

•Examining the True Alternatives (all of them)

–CONTRADICTORY claims form a true pair of alternatives

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

FALLACY:

•Hasty Generalization

–Drawing a general conclusion from a small or biased sample of evidence

o When there is not enough evidence, you are pre-judging, or guilty of PREJUDICE.

o When the evidence is not representative, or slanted, or “skewed,” it is BIASED, and your judgment is BIASED. This can be the result of a selection bias – a method of “cherry-picking” (either consciously or unconsciously) only the favorable evidence.

o “Stereotyping” is also a name for hasty generalization, or over generalization based on inadequate or unrepresentative evidence.

o “Anecdotal Evidence” typically refers to evidence that is too small and potentially biased.

CORRECT ARGUMENTATION:

•Careful, Unhasty Generalization

–Correct, careful sampling (adequate data) should be large enough and representative. Random sampling, giving each member of the population an equal chance of being selected, is the best method we have of getting a representative sample. A large, representative sample will give you a small margin of error. A margin of error of ±3 percentage points or lower is a common professional standard for polls and surveys.

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

FALLACY:

•Weak Analogy

–Comparing things that aren’t really comparable

–Comparing Apples and Oranges – for example, “When a car gets too old or broken-down and expensive to maintain, we throw it on the junk heap. Similarly, people should be thrown out, killed, when they get too old or broken-down and expensive to maintain.”

CORRECT ARGUMENTATION:

•Strong Analogy

–Comparing Apples and Oranges! (Whether a comparison is relevant depends on the context. After all, apples and oranges are both fruit.) – For example, “To get the most out of your car, you should follow good maintenance practices and get regular professional check-ups. Similarly, to get the most out of life you should maintain a healthy body and get regular check-ups with your doctor.”

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

FALLACY:

•Questionable Cause

–Includes fallacies of Misplaced Blame, such as blaming the victim or shifting the blame.

–Mistaking correlation for causation – “The more churches a city has, the more crimes a city has. Therefore, churches cause criminal behavior.” “Every time I go to an A’s game, they win. I guess they should start paying me to go to their games.”

–Oversimplified cause – “Bush came into office in January 2001, and the economy tanked in the Spring of 2001 (the recession began in March 2001, according to the National Bureau of Economic Research). Therefore, Bush caused the recession.” “Gray Davis turned our surplus into a record budget deficit.”

–Misplaced cause – Someone says, “You parked too close to my car,” when in fact they parked overlapping the space that you had to park in. They caused the cars to end up too close to each other.

–Post Hoc Ergo Propter Hoc – “First we began skipping our worship and offerings to Demeter, then the drought started. Obviously, neglecting proper treatment of the gods causes drought.”

CORRECT ARGUMENTATION:

•Correct causal reasoning is inductive, never absolute proof–it’s Inference to the Best Explanation

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

FALLACY:

•Slippery Slope Fallacy = Weak Inductive Prediction of dire consequences

a. It always takes the form of “Don’t do ______, because that will lead to dire consequences.”

b. If the prediction is supported with an inductive analogy, it is an “Appeal to Precedent,” so Slippery Slope Fallacy = Weak “Appeal to Precedent” reasoning.

c. The prediction is always based on mere possibility, not probability.

–The “Domino Effect”; predicting a “chain reaction”

–Worst-case scenario thinking

––It’s a fallacy only if the slope does not really seem to be slippery

CORRECT ARGUMENTATION:

•Strong “Appeal to Precedent” reasoning (setting-a-precedent argument)

–Doing something once usually makes it easier to do that same thing again in the future, but it does not necessarily lead to other things.

•If the slope is really slippery

–Good causal prediction (“Don’t smoke that cigarette while you put gas in your car, because you could blow us all up.”)

The Gambler’s Fallacy | Ad Hominem | Two Wrongs | Scare Tactics | Appeal to pity

Bandwagon argument | Straw man | Red herring | Begging the question/circular reasoning

Inappropriate Appeal to Authority | Appeal to Ignorance | False Alternatives

Hasty Generalization | Weak Analogy | Questionable Cause | Slippery Slope

WHAT IS A FALLACY? (TOP)

FALLACIES OF INSUFFICIENT EVIDENCE / WEAK INDUCTION