logical fallacies persuasive argument courtesy of:

Logical Fallacies

Persuasive Argument

Courtesy of: http://www.unc.edu/depts/wcweb/handouts/fallacies.html

Argument

When arguing, we use syllogisms and enthymemes to lay out our ideas.

Syllogism: 3 part logical structure

Enthymeme: 2 part, with an assumption

Syllogism in Argument

A formula for presenting an argument logically.

In its simplest form, it consists of three divisions: a major premise, a minor premise, and a conclusion

Examples of Syllogisms

Major premise: All humans are mortal (An irrefutable generalization)

Minor premise: Socrates is human (A particular instance of the generalization).

Conclusion: Therefore, Socrates is mortal.

Major premise: All public libraries should serve the people.

Minor premise: This is a public library.

Conclusion: Therefore, this library should serve the people.

Enthymeme in Argument

A syllogism in which one of the propositions, usually a premise, is understood but not stated; a rhetorical syllogism which is probable and persuasive but may not be valid.

EX: "With a name like Smucker's, it has to be good."

Example of Enthymeme

Major premise: People who own plasma TVs are rich (unstated above).

Minor premise: You own a plasma TV.

Conclusion: You are not poor.

“I trust you, you’re a teacher.”

Major premise: All teachers can be trusted.

Minor premise: You are a teacher.

Conclusion: You can be trusted.

Problems with Syllogisms/Enthymemes Major premise: All dogs are good pets.

Minor premise: Spot is a dog.

Conclusion: Spot is a good pet.

Is this always going to be true? No- there is a weakness that can lead to a fallacy.

What is Fallacy?

Fallacies are defects that weaken arguments.

First, fallacious arguments are very, very common and can be quite persuasive, at least to the causal reader or listener. You can find dozens of examples of fallacious reasoning in newspapers, advertisements, and other sources.

Second, it is sometimes hard to evaluate whether an argument is fallacious.

Different Types of Fallacies

Fallacies of Ethical Argument

Fallacies of Logical Argument

Fallacies of Emotional Argument

What does this remind you of?

Fallacies of Emotional Argument

Very common Exaggerate possible dangers well beyond

their statistical likelihood .

Example: If you don’t support the President’s tax plan, your entire family will suffer in poverty.

Either – Or / False Dichotomy

A false dilemma asserts that a complex situation can have only two possible outcomes and that one of the options is necessary or preferable.

Either go to college or forget about making money.

This falsely implies that a college education is a pre-requisite for financial success.

Was it her college education that made Britney tons of money?

Slippery Slope

Definition: The arguer claims that a sort of chain reaction, usually ending in some dire consequence, will take place, but there's really not enough evidence for that assumption. The arguer asserts that if we take even one step onto the "slippery slope,"

we will end up sliding all the way to the bottom; he or she assumes we can't stop halfway down the hill.

Example: "Animal experimentation reduces our respect for life. If we don't respect life, we are likely to be more and more tolerant of violent acts like war and murder. Soon our society will become a battlefield in which everyone constantly fears for their lives. It will be the end of civilization. To prevent this terrible consequence, we should make animal experimentation illegal right now." Since animal experimentation has been legal for some time and civilization

has not yet ended, it seems particularly clear that this chain of events won't necessarily take place.

Also known as “the Camel’s

Nose

Sentimental Appeal

Definition: The appeal to pity takes place when an arguer tries to get people to accept a conclusion by making them feel sorry for someone.

Example: "I know the exam is graded based on performance, but you should give me an A. My cat has been sick, my car broke down, and I've had a cold, so it was really hard for me to study!" The conclusion here is "You should give me an A." But the criteria for getting

an A have to do with learning and applying the material from the course; the principle the arguer wants us to accept (people who have a hard week deserve A's) is clearly unacceptable.

Example: “Exxon Mobil’s oil spill killed thousands of baby seals, therefore we should no longer depend on oil as an energy source.”

Bandwagon Appeal

Encourages the audience to agree because everyone else is doing so.

Example: Everyone in society is supporting gay marriage, therefore you should support gay marriage too.

Fallacies of Ethical Argument

Appeal to False Authority

Definition: Often we add strength to our arguments by referring to respected sources or authorities and explaining their positions on the issues we're discussing. If, however, we try to get readers to agree with us simply by

impressing them with a famous name or by appealing to a supposed authority who really isn't much of an expert, we commit the fallacy of appeal to authority.

Example: "We should abolish the death penalty. Many respected people, such as actor Guy Handsome, have publicly stated their opposition to it." While Guy Handsome may be an authority on matters having to

do with acting, there's no particular reason why anyone should be moved by his political opinions--he is probably no more of an authority on the death penalty than the person writing the paper.

Poisoning the Well

Discredit what a person might later claim by presenting unfavorable information about the person.

Example: Of course, this liar will tell you that he didn’t steal my stuff. You can’t believe a thief. Go ahead and ask him. He’ll deny it.

Straw Man

Definition: A person simply ignores a person’s actual position and substitutes a distorted, exaggerated or misrepresented version of that position.

Example:

A: We need to regulate access to handguns B: My opponent believes that we should ignore the rights guaranteed to

us as citizens of the United States by the Constitution. Unlike my opponent, I am a firm believer in the Constitution,and a proponent of freedom.

Ad Hominem Latin for to the man

Directly attacks someone’s appearance, personal habits, or character rather than focusing on the merit of the issue at hand. The implication is that if something is wrong with this person, whatever he/she says must be wrong.

How can you say he’s a good musician when he’s been in and out of rehab for three years?

Fallacies of Logical Argument

Hasty Generalization A hasty generalization is a conclusion based on

insufficient or unrepresentative evidence. Stereotyping and Sexism are forms of this fallacy.

Take, for example common dumb blonde jokes:

Q: What do you call a blonde skeleton in the closet?

A: Last year's hide-and-go-seek winner.

Faulty Causality/Post Hoc Fallacy

This fallacy assumes that just because B happened after A, it must have been caused by A.

Politicians love this one.

Faulty Causality (Post hoc)

This fallacy gets its name from the Latin phrase "post hoc, ergo propter hoc," which translates as "after this, therefore because of this."

Definition: Assuming that because B comes after A, A caused B. Of course, sometimes one event really does cause another one that comes

later--for example, if I register for a class, and my name later appears on the roll, it's true that the first event caused the one that came later. But sometimes two events that seem related in time aren't really related as cause and event. That is, correlation isn't the same thing as causation.

Examples: "President Jones raised taxes, and then the rate of violent crime went up. Jones is responsible for the rise in crime.“ The increase in taxes might or might not be one factor in the rising crime

rates, but the argument hasn't shown us that one caused the other.

Faulty Causality ExampleSince Governor Bush took office, unemployment of minorities in the state has decreased by seven percent. Governor Bush should be applauded for reducing unemployment among minorities.

Before we pat the governor on the back, the

speaker must show that Bush’s policies are responsible for the decrease in unemployment. It is not enough to show the decrease came after his election.

Begging the Question

This is a kind of circular argument where the support only restates the claim.

Wrestling is dangerous because it is unsafe.

Jogging is fun because it is enjoyable.

Unsafe means the same thing as dangerous and fun means the same thing as enjoyable. This makes the reasoning circular.

(Latin for “It doesn’t follow”) is a statement that does not logically relate to what comes before it. An important logical step may be missing in such a claim.

Example: If those protesters really loved their country, they wouldn’t question the government.

OR:

Claim: You must not love me…

Reason: …b/c you haven’t bought me that bike.

Warrant: Buying bikes for children is essential to loving

them.

False Analogy

Definition: Many arguments rely on an analogy between two or more objects, ideas, or situations. If the two things that are being compared aren't really alike in the relevant respects, the analogy is a weak one, and the argument that relies on it commits the fallacy of weak analogy.

Example: "Guns are like hammers--they're both tools with metal parts that could be used to kill someone. And yet it would be ridiculous to restrict the purchase of hammers--so restrictions on purchasing guns are equally ridiculous." While guns and hammers do share certain features, these

features (having metal parts, being tools, and being potentially useful for violence) are not the ones at stake in deciding whether to restrict guns. Rather, we restrict guns because they can easily be used to kill large numbers of people at a distance. This is a feature hammers do not share--it'd be hard to kill a crowd with a hammer. Thus, the analogy is weak, and so is the argument based on it.

False Analogy Example

If we can put a man on the moon, why can’t we find the cure for the common cold?

While both things being compared here are related to science, there are more differences than similarities between space and biological advancements.

Red Herring

Definition: Partway through an argument, the arguer goes off on a tangent, raising a side issue that distracts the audience from what's really at stake. Often, the arguer never returns to the original issue.

Example: "Grading this exam on a curve would be the most fair thing to do. After all, classes go more smoothly when the students and the professor are getting along well." Let's try our premise-conclusion outlining to see what's wrong with this argument: Premise: Classes go more smoothly when the students and the professor are getting

along well. Conclusion: Grading this exam on a curve would be the most fair thing to do.

When we lay it out this way, it's pretty obvious that the arguer went off on a tangent--the fact that something helps people get along doesn't necessarily make it more fair; fairness and justice sometimes require us to do things that cause conflict. But the audience may feel like the issue of teachers and students agreeing is important and be distracted from the fact that the arguer has not given any evidence as to why a curve would be fair.

Can you name this Fallacy?

1) It is ridiculous to have spent thousands of dollars to rescue those two whales trapped in the Arctic ice. Why look at all the people trapped in jobs they don’t like.

RED HERRING


2) Plagiarism is deceitful because it is dishonest.

BEGGING THE QUESTION


3) Water fluoridation affects the brain. Citywide, student’s test scores began to drop five months after fluoridation began.

FALSE CAUSALTY


4) I know three redheads who have terrible tempers, and since Annabel has red hair, I’ll bet she has a terrible temper too.

HASTY GENERALIZATION


5) Supreme Court Justice Byron White was an All-American football player while in college, so how can you say that athletes are dumb?



6) Why should we put people on trial when we know they are guilty?

BEGGING THE QUESTION


7) You support capital punishment just because you want an “eye for an eye,” but I have several good reasons to believe that capital punishment is fundamentally wrong…

STRAW MAN


8) The meteorologist predicted the wrong amount of rain for May. Obviously the meteorologist is unreliable.



9) You know Jane Fonda’s exercise video’s must be worth the money. Look at the great shape she’s in.

FALSE CAUSALTY


10) We have to stop the tuition increase! The next thing you know, they'll be charging $40,000 a semester!

SLIPPERY SLOPE


11) The book Investing for Dummies really helped me understand my finances better. The book Chess for Dummies was written by the same author, was published by the same press, and costs about the same amount, so it would probably help me understand my finances as well.

FALSE ANALOGY


12) Look, you are going to have to make up your mind. Either you decide that you can afford this stereo, or you decide you are going to do without music for a while.

EITHER-OR


13) I'm positive that my work will meet your requirements. I really need the job since my grandmother is sick.

SENTIMENTAL APPEALS

logical fallacies persuasive argument courtesy of:

Documents

conclusion slide

assumption slide

rhetorical syllogism

college education

fallacious arguments

logical structure enthymeme

fallacious reasoning

good pets