Fallacies A Fallacy is simply an error in reasoning: an argument that, for one reason or another, has no logical strength. In general, an argument without logical strength can be ignored.

But some types of error in reasoning are so common, and so persuasive, that they are worth singling out.

Fallacies A Fallacy is simply an error in reasoning: an argument that, for one reason or another, has no logical strength. In general, an argument without logical strength can be ignored.

But some types of error in reasoning are so common, and so persuasive, that they are worth singling out.

We will study several of these for 2 reasons: 1. Identifying them helps to avoid being tricked by them.

2. Identifying them clarifies what makes an argument logically strong.

We know that there are only two ways an argument can be bad:

irrelevant

premises: they do not support the conclusion

unacceptable

premises: they are not true, or not proper.

Fallacies with Irrelevant Premises Division

: inferring that a part or individual has a property simply because the whole or the group does.

Fallacies with Irrelevant Premises Division

: inferring that a part or individual has a property simply because the whole or the group does.

“Most tax comes from the middle class, so middle class people pay more in tax than the rich do.” Even though it is true that the group of middle class people pay more in tax than the group of rich people, it does not follow that any middle class person pays more than every (or even any) rich person.

Composition

: inferring that a whole or group has a property simply because its parts or members do.

Composition

: inferring that a whole or group has a property simply because its parts or members do.

“Sugar Bomb Triple Chocolate cereal is good for you because it has added vitamin C, and everyone knows vitamin C is good for you!” Even though it is true that Vitamin C is good for you, it does not follow that everything composed of Vitamin C is also good for you. It might contain bad things, or be on balance bad.

Appeal to the Person (Ad Hominem)

: rejecting a claim by criticizing the person who makes it rather than the claim itself.

U sing a negative trait of a speaker as evidence that his statement is false or that his argument is weak.

X says that P, but X has a negative trait, so X is wrong (or: X’s argument is not any good).

Abusive Ad Hominem

: rejecting someone’s claim or argument by verbally abusing them.

“Poet Allen Ginsberg has argued in favor of abolishing censorship of pornographic literature. But he is a pot smoking homosexual. So, his arguments are nothing but trash. Ginsberg’s argument might still be a good one, even if he is morally corrupt.

Tu Quoque Ad Hominem

: rejecting someone’s claim or argument by charging them with hypocrisy.

“I can’t believe George Bush is arguing for campaign finance reforms. He is one of the worst offenders ever. His arguments are worthless.” Even a hypocrite can have a good argument.

Poisoning the Well

: rejecting a person’s claims or argument by mentioning irrelevant facts about the arguer, in order to cast doubt on her argument.

“The publisher of Hustler has argued in favor of abolishing censorship of pornographic images. But he is hoping to cash in when the laws are further relaxed. So we shouldn’t listen to him.” The publisher’s argument might still be valid, even if he has a lot to gain by the truth of the conclusion.

NOTE: these fallacies involve someone responding to a person’s claim or

argument

by criticizing the

person

. But it can be OK to criticize a person, if the conclusion is about that person.

NOTE: these fallacies involve someone responding to a person’s

argument

by criticizing the

person

, and not the argument. But it can be OK to criticize a person, if the conclusion is about that person. “I can’t believe George Bush is arguing for campaign finance reforms. He is one of the worst offenders ever. So, he is such a hypocrite.” This does not commit any fallacy at all.

Equivocation

: using a word in two different meanings in the premises and/or conclusion.

“Letter grades are a simplistic and arbitrary method for evaluating students. So, students should not be graded.”   “Grade” is ambiguous: A particular system of evaluation.

Evaluation itself.

Subjectivism

: using the fact that one believes or wants a proposition to be true as evidence that it is true.

Often in cases of moral or religious beliefs.

E.g., “I was just brought up to believe that...” “I have just always believed that….” “It might be true for you, but it is not true for me that….” The fact that somebody believes something is not itself evidence that that belief is true. For anybody can make a mistake.

It is, of course, logically OK for somebody to use one of these phrases to express an opinion. But not if they are trying to give an argument for their opinion.

Appeal to popularity

: using the fact that many people believe a proposition as evidence that it is true.

E.g., “The US should stay in Iraq because most Americans believe that we should.”

Appeal to tradition

: “Privatized medicine is better for the US because it is our traditional way.” To say that a policy or practice is traditional is just to say that, in the past, most people believed in it. But even the majority can make a mistake.

Appeal to Emotion

: trying to get someone to believe a proposition on the basis of an emotion one makes them feel.

Patriotism

: “You should support the new Education policy because it is the American Way.”

Snobbery

: “Only the most discriminating appreciate the luxury of a Rolls Royce. You deserve one.”

Appeal to Emotion

: trying to get someone to believe a proposition on the basis of an emotion one makes them feel.

Patriotism

: “You should support the new Education policy because it is the American Way.”

Snobbery

: “Only the most discriminating appreciate the luxury of a Rolls Royce. You deserve one.” Of course, sometimes it is OK to appeal to emotions to convince someone that they ought to

do

something.

e.g., appealing to their shame, guilt or pity.

But, whether a proposition is true has nothing to do with how it makes you feel.

Appeal to Force

: trying to get someone to accept a proposition on the basis of a threat.

“If you don’t believe me, we’re through.”

Appeal to ignorance

: using the absence of proof for a proposition as evidence for the truth of the opposing proposition.

It is not proven that P is false So, P must be true.

E.g., The LA police investigating the Simpson murder did not discover any evidence linking anybody but O.J. Simpson to the murder. If someone else had committed the killings, the police would have found evidence. Since they found no evidence, it must be that O.J. Simpson is the murderer.

2 exceptions: SCIENCE: If attempts to prove or disprove some claim have been done in a systematic way, then the appeal to ignorance might not be fallacious.

e.g., the fact that scientists have been trying without success for years to prove that gold can be made from copper suggests that it cannot be done.

2 exceptions: SCIENCE: If attempts to prove or disprove some claim have been done in a systematic way, then the appeal to ignorance might not be fallacious.

e.g., the fact that scientists have been trying without success for years to prove that gold can be made from copper suggests that it cannot be done.

In a COURT of law: our system of justice holds that a suspect must be assumed to be innocent of a crime unless enough of the right kind of evidence can be found. e.g., what about the O.J. Simpson case?

Sometimes, and appeal to ignorance takes the form of a “Where do we draw the line?” argument: If we allow same sex marriage, then how can we prevent three way marriages or marriages between sisters and brothers, or parents and their children? Where would we draw the line?

Just because we do not know where to draw a certain line does not mean there is no line. This is an appeal to ignorance.

Diversion

: trying to support one proposition by arguing for another.

STRAW MAN

: the distorting weakening or oversimplifying of someone’s position so it can be more easily attacked or refuted.

“What I object to most about those people who oppose capital punishment is that they believe that the lives of convicted murderers are more important than the lives of the policemen and prison guards who protect us, and that is just false.”

RED HERRING

: the deliberate raising of an irrelevant issue during an argument.

“Critics of the automobile industry frequently claim that our cars are not as safe as they could be. What these critics so conveniently forget is that cars do not cause accidents. Accidents are caused by bad drivers.”

Unacceptable Premises Begging the Question

: trying to support a proposition with an argument in which that proposition is a premise.

C

apital punishment is sometimes a quite legitimate and appropriate form of punishment.

So, capital punishment is sometimes justified.

The argument simply says the same thing in the conclusion as it says in the premise. In effect, the arguer is simply supporting her conclusion by stating it in different terms. So, the only reason one would find this argument persuasive is if one already believed the conclusion.

Ford Motor Company clearly produces the best cars in America. We know they do because they hire the best designers and engineers. And they can do this because they make more profits than other companies. And they can afford higher salaries because they produce the best cars in America.” The arguer is going in a circle. The argument for the conclusion includes a premise which she in turn tries to support by appealing to that very conclusion.

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Complex Question

: asking a question in such a way that no matter how it is answered, the answer presupposes something controversial e.g., Have you stopped cheating on exams yet?

Answering YES, implies that you did cheat and have stopped.

Answering NO, implies that you have cheated and that you have not yet stopped!

So it is a trick question, intended to trap the respondent.

False Alternative

: excluding relevant possibilities without justification.

Either P or Q Not P Therefore Q.

This type of reasoning is a fallacy when P and Q are not the only possibilities.

False Alternative

: excluding relevant possibilities without justification.

Either P or Q Not P Therefore Q.

This type of reasoning is a fallacy when P and Q are not the only possibilities.

“Either Bill Clinton was telling the truth when he said he and Monica never had sexual relations or he was lying. We now know that they did have sexual relations. So, Clinton lied.” Maybe Clinton genuinely believed they did not have sexual relations. Lying requires not really believing what you say. So there are more possibilities here than this argument supposes.

Slippery Slope Argument

: Arguing, without good reasons, that taking a particular step will inevitably lead to a further, undesirable step or steps.

All Americans should be against laws permitting same-sex marriage. If we allow those, then soon we’ll have to allow three way marriages and even man-animal marriages too!

There may be good arguments against same sex marriage. But it is unlikely to produce these negative results.

Sometimes, a slippery slope argument looks like a “where do we draw the line argument”: If we allow people to drink when they are 20, then we might as well let them drink when they are 19, or even 18, and then where do we draw the line? We have to draw the line somewhere, so we should keep the drinking age at 21.

This is an appeal to ignorance and also a slippery slope argument. In either form it is not any good.

Hasty Generalization

: inferring a general proposition from an inadequate sample of particular cases.

General propositions: e.g., All Fords are reliable.

All ravens are black.

George is always late for class.

Something is true in these cases.

So, that thing is always true.

To decide whether George really is always late, one has to examine a large number of different kinds of cases: Is he always late for class, for meetings, for dinner, for bed, …..?

So a hasty generalization can result either from: too few cases not enough variety of cases.

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Appeal to Authority

: using testimony as evidence when the authority is not credible or when there are no possible authorities.

X says that P is true, and X is a credible authority, therefore P is true Testimony is credible only when it is: a. Appropriate: there are no experts on matters of taste, or personal preference, such as whether oysters taste good.

b. Competent: i) expertise: the witness must be properly trained in the relevant field.

ii) Informed: the witness must have studied the relevant facts of the case.

c. Unbiased: the witness must not be biased in any way.

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Appeal to Authority

: using testimony as evidence when the authority is not credible or when there are no possible authorities.

X says that P is true, and X is a credible authority, therefore P is true Testimony is credible only when it is: a. Appropriate: there are no experts on matters of taste, or personal preference, such as whether oysters taste good.

b. Competent: i) expertise: the witness must be properly trained in the relevant field.

ii) Informed: the witness must have studied the relevant facts of the case.

c. Unbiased: the witness must not be biased in any way. NOTE: even if the witness is not credible the testimony might still be true.

James W. Johnston, Chairman of R.J. Reynolds Tobacco Company, testified before Congress that tobacco is not an addictive substance and that smoking cigarettes does not produce any addiction. Since his company produces, tests and sells tobacco he probably knows what he is talking about. Therefore, we should believe him and conclude that smoking does not in fact lead to any addiction.

The argument’s structure: 1. Johnson says that tobacco is not addictive.

2. Johnson is a credible authority 3. Tobacco is not addictive.

The second premise is questionable .

James McDermott of Greenpeace, one of the leading environmental protection groups in the world, claims that the paper industry is destroying American forests by employing unsustainable harvesting practices. Mr. McDermott is a trained forest engineer who worked for 20 years with one of the largest American forestry companies before joining Greenpeace. We should believe what he says.

The argument’s structure: 1. McDermott says that the paper industry is ….

2. McDermott is a credible authority.

3. So, the paper industry is… Again, the second premise is questionable.

Not in text

Post Hoc

: using the fact that one event preceded another as sufficient evidence for the conclusion that the first caused the second.

A occurred before B So, A caused B Sometimes, it is just a coincidence that A occurred before B.

Not in Text

Post Hoc

: using the fact that one event preceded another as sufficient evidence for the conclusion that the first caused the second.

A occurred before B So, A caused B Sometimes, it is just a coincidence that A occurred before B.

“The economy rebounded after the tax cuts were voted in. They must be what caused the economy to turn around.” Though it is true that a cause precedes the effect, that is only part of what makes something a cause.

Faulty Analogy: An argument in which the things

being compared are not sufficiently similar in the relevant respects.

X is like Y Something is true of Y So:, that should be true of X too.

An argument by analogy is logically good only when:

• •

the compared things are

relevantly

similar.

the compared things are

sufficiently

similar.

The internet is just like any other highway, and so just as there are laws governing highways, so there should be laws governing the internet.

There are similarities between the internet and highways, but these are not

relevant

to the question of laws.

The war in Iraq is just like the war in Vietnam, and just as we lost that war, so we will lose this war.

There are relevant similarities between the two wars, but it is not clear that they are

sufficiently

similar, since there are important differences too.

I strongly object to the proposed sale of alcoholic beverages at County Golf Course. The idea of allowing people to drink wherever and whenever they please is positively disgraceful and can only lead to more alcoholism and all the problems it produces—drunk driving, perverted parties and who knows what else. I’m sure General Stuart, if he were alive today to see what has become of the land he deeded to the county would disapprove strenuously.

Nobody knows what really happened in the hotel room between Bill Clinton and Paula Jones. And we will never find out the truth because everybody is out to protect themselves or else to make money. So we should just assume that Bill Clinton is not guilty of sexual assault against Ms. Jones.

My opponents have argued against the need for new B-1 bombers, claiming that they are not reliable enough. But I reject these arguments. In my view, America needs a strong defense. We’d all like to live in peace with the other nations of this world, but we deceive ourselves if we think we can do without being prepared to defend ourselves and our allies, our rights and our interests. It is a dangerous world out there, and I’d be failing to do my duty to the people of this nation if I allowed us to lie down and cry “Uncle”. Do not let my opponent’s arguments persuade you.