Logic 2: Fallaciestothzit.weebly.com/uploads/1/0/6/7/10676184/0117_logic2.pdf · Logic 2: Fallacies Jan. 17, 2014. What is a fallacy?Fallacies of RelevanceDefective InductionFallacies

What is a fallacy? Fallacies of Relevance Defective Induction Fallacies of Presumption Ambiguity Summary

Logic 2: Fallacies

Jan. 17, 2014

Logic 2: Fallacies Jan. 17, 2014


Overview IWhat is a fallacy?

DefinitionFormal and Informal Fallacies

Fallacies of RelevanceAppeal to EmotionAppeal to PityAppeal to ForceArgument Against the PersonIrrelevant conclusionSummary

Defective InductionFallacy of IgnoranceAppeal to Inappropriate AuthorityFalse CauseHasty Generalization



Overview IISummary

Fallacies of PresumptionFallacy of AccidentComplex QuestionBegging the QuestionSummary

AmbiguityEquivocationAmphibolyFallacy of CompositionFallacy of DivisionSummary

Summary


What is a fallacy? Fallacies of Relevance Defective Induction Fallacies of Presumption Ambiguity SummaryDefinition Formal and Informal Fallacies

When an argument goes wrong. . .

An argument can go wrong in many ways.some (or all) of the premises are obviously falsethe conclusion does not follow — it has the wrong form(invalid argument)inductive arguments can also go wrong in many waysBut sometimes these mistakes are very subtle and hard tonotice.

Fallacy:When the premises of an argument appear to support theconclusion, but do not in fact do so, we say that the argument isfallacious. By ‘fallacy’ we mean typical errors that often occur, andare often deceiving.


What is a fallacy? Fallacies of Relevance Defective Induction Fallacies of Presumption Ambiguity SummaryDefinition Formal and Informal Fallacies

Formal and Informal Fallacies

Note: all we will talk about here are informal fallacies, that is,cases where the argument goes wrong in some obvious way, and wedo not need formal logic to discover the fallacy. (This means thatthere are also formal fallacies, and we will treat them later.)


What is a fallacy? Fallacies of Relevance Defective Induction Fallacies of Presumption Ambiguity SummaryAppeal to Emotion Appeal to Pity Appeal to Force Argument Against the Person Irrelevant conclusion Summary

Example“As all clear-thinking residents of our fine state have alreadyrealized, the Governor’s plan for financing public education isnothing but the bloody-fanged wolf of socialism cleverly disguisedin the harmless sheep’s clothing of concern for children. Therefore,the Governor’s plan is bad public policy.”

What’s wrong with this? Does the conclusion follow? Why?

Appeal to emotion — ad populumThe argument relies on emotion rather than on reason: In place ofevidence, it uses expressive language to excite enthusiasm for oragainst some cause. But the occurrence of this enthusiasm hasnothing to do with the truth of the conclusion.



Example“I am a single parent, solely responsible for the financial support ofmy children. If you give me this traffic ticket, I will lose my licenseand be unable to drive to work. If I cannot work, my children and Iwill become homeless and may starve to death. Therefore, youshould not give me this traffic ticket.”

What’s wrong now? Can the premises be true and theconclusion false?

Appeal to pity — ad misericordiamAgain, the argument relies on emotion rather than on reason: ittries to convince you by pointing out the unfortunate consequencesthat will otherwise follow, for which we would then feel sorry. Thetruth of the premises, again, has nothing to do with the truth ofthe conclusion.



Example“If you do not agree with my opinions, you will receive a grade ofF for this course. I believe that Aristotle was the greatestphilosopher of all times. Therefore, Aristotle was the greatestphilosopher of all times.”

Can the premises be true and the conclusion false? What ifthe conclusion is also true?

Appeal to force — ad baculumSomeone in a position of power threatens to bring aboutunfortunate consequences for anyone who dares to disagree withhis/her proposition. While this might be an effective way to getyou to agree (or at least to pretend to agree) with my position, itoffers no reasons for believing it to be true.



Example“Before he died, poet Allen Ginsberg argued in favor of legalizingpornography. But Ginsberg’s arguments are nothing but trash: hesmoked marijuana and was an advocate of the drug culture.”

It is one of the most common fallacies; very often occurs, andwe don’t even notice it.

Argument against the person — ad hominemInstead of arguing against someone’s opinion, the argumentattacks the person who holds that opinion by showing him asdisreputable in some way. So it is saying that the opinion must befalse because of the person who believes it to be true. (But again,personality is irrelevant to truth!)



Example“All children should have ample attention from their parents.Parents who work full-time cannot give ample attention to theirchildren. Therefore, mothers should not work full-time.”

Do we have an argument here? Does the conclusion follow?Why?

Irrelevant conclusion — ignoratio elenchiThe speaker tries to establish the truth of a proposition by offeringan argument that actually provides support for an entirely differentconclusion. It can often distract the audience, and we don’t noticethat the conclusion just misses the point.



2 especially common cases of irrelevant conclusion:

Red herring:A deliberate attempt to change the subject ordivert the argument from the real question atissue to some side-point.

Example“I should not pay a fine for reckless driving. There are many otherpeople on the street who are dangerous criminals and rapists, andthe police should be chasing them, not harassing a decenttax-paying citizen like me.”



2 especially common cases of irrelevant conclusion:

Straw man:An attempt to establish a conclusion byoverstating, exaggerating, or over-simplifyingthe arguments of the opposing side.

ExampleI say: “New York should increase funding to unemployed singlemothers during the first year after childbirth because they needsufficient money to provide medical care for their newbornchildren.” The other side: “My opponent believes that someparasites who don’t work should get a free ride from the tax moneyof hard-working honest citizens. I’ll show you why he’s wrong . . .”



Summary: Fallacies of Relevance

Fallacies of relevance are bald mistakes; they might better becalled fallacies of irrelevance: they point to the absence of any realconnection between the premises and the conclusion of theargument.

Since there is no connection, the premises cannot possiblyestablish the truth of the conclusion.But the premises are usually psychologically relevant: theyhave some emotional impact on the readers.



Summary: Fallacies of Relevance

1 Appeal to emotion2 Appeal to pity3 Appeal to force4 Argument against the person5 Irrelevant conclusion


What is a fallacy? Fallacies of Relevance Defective Induction Fallacies of Presumption Ambiguity SummaryFallacy of Ignorance Appeal to Inappropriate Authority False Cause Hasty Generalization Summary

Example“No one has conclusively proven that there is no intelligent life onthe moons of Jupiter. Therefore, there is intelligent life on themoons of Jupiter.”

Again, the conclusion does not follow; the opposite has notbeen proven either.Notice that the procedure is sometimes used rightly! E.g., incourt.

Fallacy of ignorance — ad ignorantiamThe speaker asserts something only because the opposite has notbeen proven. But from this, the conclusion does not follow: theopposite might still be true, just no proof found (yet), or maybe itcannot be proven for some reason.



Example“The former Governor believes that aliens have landed in theArizona desert, so aliens must have landed in the Arizona desert.”

Why does it matter what the Governor believes?

Appeal to inappropriate authority — ad verecundiamTries to establish a conclusion by appeal to an improper authority,such as a famous person or a source that may not be reliable forsome reason (e.g., biased authority). Since we know the person, orbelieve that he has some sort of knowledge, we assume that he hasknowledge about things outside his expertise too.



Example“A black cat crossed my path at noon. An hour later, my motherhad a heart-attack. So the black cat must have caused the badluck.”“The death penalty in the US has given us the highest crime rateand greatest number of prisoners per 100,000 population in theindustrialized world.”

From the fact that one event was before another one, can weinfer that the latter was caused by the former?

False cause — post hoc, ergo propter hocA fallacy that occurs when the writer mistakenly assumes that,because the first event preceded the second event, it must meanthe first event caused the later one. Sometimes it does, butsometimes it doesn’t. But if it does, we have to establish it insteadof just assuming.



Example“Take my son, Martyn. He’s been eating fish and chips his wholelife, and he just had a cholesterol test, and his level is below thenational average. What better proof could there be than a fryer’sson?”

Is the sample a good sample? Did we examine enough /representative cases before drawing the conclusion?

Hasty generalization — dicto simpliciterDraws a general conclusion without examining all the relevantdata. Of course, very often we can’t examine everything; but still,the sample must be carefully selected, and large enough.



Summary: Fallacies of Defective Induction

Unlike in the previous category (fallacies of relevance), in this casethe premises are relevant to the conclusion. The problem is thatthey are inadequate: they are simply insufficient to establish theconclusion.

1 Fallacy of ignorance2 Appeal to inappropriate authority3 False cause4 Hasty generalization


What is a fallacy? Fallacies of Relevance Defective Induction Fallacies of Presumption Ambiguity SummaryFallacy of Accident Complex Question Begging the Question Summary

Example“Suppose that a friend in his right mind has deposited arms withme and asks for them when he is not in his right mind. Ought I togive the weapons back to him? Of course: everyone agrees thatyou should give back what you borrow.”

Is the general rule correct? How general is it?

Fallacy of accidentIt occurs when one applies a general rule to a particular case whenaccidental circumstances render the general rule inapplicable.What is true in general might not be true absolutely universallyand without qualification.



Example“With all of the hysteria, and phony science, could it be thatman-made global warming is the greatest hoax ever perpetrated onthe American people?”

What kind of question is it? What answer is the speakerexpecting?

Complex question fallacyA question is asked in a way that presupposes the truth of someproposition hidden within the question. The question is oftenrhetorical, no answer is genuinely asked. But if we analyze it, itmight turn out that the questioner is presupposing something false.



Example“To allow every man unbounded freedom of speech, must alwaysbe, on the whole, advantageous to the state; for it is highlyconducive to the interests of the community that each individualshould enjoy a liberty, perfectly unlimited, of expressing hissentiments.”

Which are the premise and the conclusion? Do they reallydiffer?

Begging the question — petitio principiiOccurs when one assumes the truth of what one tries to prove.Can be very obvious, but not always! Also occurs in circulararguments, when I show that a is true because of b, b is truebecause of c, and c is true because of a.



Summary: Fallacies of Presumption

These are arguments that are based on some tacit (thereforeunjustified) assumption. The assumption might even be true, butif it is unjustified, it cannot help to establish the conclusion. Thatthe assumption is implicit might be either deliberate (when theauthor tries to hide some questionable claims), or just anoversight. It also might be the case that the author thinks theassumption is obvious, when in fact it is not.

1 Fallacy of accident2 Complex question3 Begging the question


What is a fallacy? Fallacies of Relevance Defective Induction Fallacies of Presumption Ambiguity SummaryEquivocation Amphiboly Fallacy of Composition Fallacy of Division Summary

Example“An elephant is an animal. Therefore, a small elephant is a smallanimal.”“Apples are fruits. My computer is an apple. Therefore, mycomputer is a fruit.”

What is funny in these arguments?

EquivocationOccurs when a term or phrase is used in different senses in thepremises and in the conclusion. It often occurs with relative terms(‘small’, ‘tall’, etc.), and those cases can be harder to notice.



Example“The tour guide said that standing in Greenwich Village, theEmpire State Building can easily be seen. Thus, the Empire StateBuilding is in Greenwich Village.”

What is the misleading point here?

Amphiboly — “two in a lump”Depends on an amphibolous statement, the meaning of which isindeterminate because of the way its words are combined. Anamphibolous statement might be true in one interpretation andfalse in another; when it is used in the premise in oneinterpretation, and the conclusion is drawn based on the other one,that’s a fallacy.



Example“Since a bus uses more gas than an automobile, therefore all busesuse more gas than all automobiles.”“Since every part of a helicopter is lightweight, it follows that thewhole helicopter is lightweight.”

Why does not the conclusion follow? Are there cases when itwould follow?

Fallacy of CompositionAn inference from the property of the parts to the property of thewhole. Sometimes such inference is a valid one, but not always —we need to check whether it works in the actual context.



Example“American Indians are disappearing. That man is an AmericanIndian. Therefore, that man is disappearing.”“Many people have dogs. Afghan hounds are dogs. Therefore,many people have Afghan hounds.”

Why does not the conclusion follow? Are there cases when itdoes?

Fallacy of DivisionThe opposite of the fallacy of composition; here, it argues thatwhat is true of a whole must also be true of its parts. Again,sometimes such an argument works, but we must be very carefulwith the form of the argument.



Summary: Fallacies of Ambiguity

The meaning of words of phrases may shift as a result ofinattention, or deliberately within a course of an argument: a termmay have one sense in a premise, but a different sense in theconclusion. If the inference depends on such changes in meaning,the argument is fallacious.

1 Equivocation2 Amphiboly3 Fallacy of composition4 Fallacy of division



Summary: The ways an argument can go wrong

Fallacies of relevance1 Appeal to emotion2 Appeal to pity3 Appeal to force4 Argument against the

person5 Irrelevant conclusion

Fallacies of presumption1 Fallacy of accident2 Complex question3 Begging the question

Fallacies of defective induction1 Fallacy of ignorance2 Appeal to inappropriate

authority3 False cause4 Hasty generalization

Fallacies of ambiguity1 Equivocation2 Amphiboly3 Fallacy of composition4 Fallacy of division


Documents

Logic 2: Fallaciestothzit.weebly.com/uploads/1/0/6/7/10676184/0117_logic2.pdf · Logic 2: Fallacies Jan. 17, 2014. What is a fallacy?Fallacies of RelevanceDefective InductionFallacies