LOGIC 101: Introduction to Persuasive Methods

What is a PREMISE and how does it relate to a CONCLUSION?

How could a FALSE PREMISE lead to an INVALID CONCLUSION?

Errors in LOGIC (Logical Fallacies)

Red HerringThe name of this fallacy comes from the

sport of fox hunting in which a dried, smoked herring, which is red in color, is dragged across the trail of the fox to throw the hounds off the scent.

Thus, a "red herring" argument is one which distracts the audience from the issue by introducing something that is irrelevant.

The Red Herring fallacy occurs where someone introduces an irrelevant point into an argument. He may think (or he may want us to think) it proves his side, but it really doesn’t.

Here’s how it works:Topic A is under discussion.Topic B is introduced under the guise of

being relevant to topic A (when topic B is actually not relevant to topic A).

Topic A is abandoned.

Examples of Red Herring:Grizzly bears can’t be dangerous – they look

so cute.You shouldn’t give us homework - it’s

raining and its supposed to be a bad storm!"I think there is great merit in making the

requirements stricter for the graduate students. I recommend that you support it, too. After all, we are in a budget crisis and we do not want our salaries affected."

Slippery SlopeArgues that A will cause B, then C, D,

E….. all the way downhill to Z!Much of it is based on assumption.

Examples of slippery slope arguments:

Kids start out using the internet to do their schoolwork, but it isn’t long before they start surfing the net and chatting with perverts wearing leather and using fake names in chat rooms. Next thing you know, they start meeting pedophiles in malls and end up dead. So, I don’t let my kids use the internet.

Today its gay marriage, and tomorrow they’ll be asking to legalize polygamy. Then marriage between family members. What about to pets? After all, animals have rights too, don’t they?

One more slippery slope… “If you give us homework, then I’m going to

have to stay up late. If I do that, I’m probably going to get sick just like my little sister who has a fever of 106 and is throwing up everything. Then , I’m going to do horrible at baseball tryouts, and I’ll never make Varsity. So, I’ll have to forget the major leagues, abandon my childhood dreams, and resign myself to collecting cans for a living. But, if you want to go ahead and give us homework, I can’t stop you; you’re the teacher.”

OversimplificationArguer claims that A causes B to occur,

when in fact several causes may be responsible for event B to occur.

Examples of oversimplification:Only 72% of high school kids graduate from

college in our town. The teachers are just not doing their jobs!

Over the past ten years, the crime rate has been rising, and so has the number of illegal immigrants crossing the border. As soon as they come over, that’s when the problems start.

Signal of oversimplification:The arguer makes a complex problem sound

simple and easy to fix

Either/or reasoningThe arguer illegitimately claims that there are only 2

alternatives in a situation when there are actually more

Examples of either/or reasoning:

“Eat your vegetables. You don’t want to die of malnourishment, do you?”

“Are you going to stay in college, or are you going to scrape around forever looking for a good job?” (It is possible to get a good job and not go to college)

“We either fight back and invade Iraq, or we let the terrorists have their way.”

Circular logicThe argument claims to prove a conclusionBUTThe conclusion has already been assumed as

a premise

Examples of circular logic:McDonald’s is the best place to eat because

so many people eat there and so many people don’t eat at a restaurant if its not the best place to eat.

Bush on unity of the Republican party: “I am confident there will be (unity). I’m confident people are coming together. And the reason I believe this is because our party is united.”

More Examples of circular logic

Senator Flummox on gay marriage: “I oppose gay marriage because two people of the same sex should not be entitled to the same privileges that married couples are entitled to.”

Bush on whether he will run for president: “There is a lot of speculation and I guess there is going to continue to be a lot of speculation until the speculation ends.” (Austin American-Statesman, October 18, 1998).

Signals of circular logic:An arguer keeps repeating a claim as if he has

given evidence to support a conclusion.This is actually a ploy to avoid giving any

justification

Begging the question:Called “begging the question” because at the

end of an argument the careful listener still has questions such as , “but how do you know…?”

This kind of logic is false because the arguer assumes part of the conclusion in one of the premises.

Examples of begging the question:God exists because the Bible says so. The

Bible was written by God. That restaurant has the best food in town,

because it has the best chef. It attracted the best chef in town because it had the best reputation. It got the best reputation by serving the best food.

I am not a liar

The Bare Assertion Definition: to close a debate with a

simple declaration that it's over simply because you say so.

Example: Son: Dad, can I have the car tonight? Father: Nope. Son: Why not? Father: Because I said so.

These phrases are bare assertions

Because I said so. That's just the way it is. That's all there is to it. Trust me.

Other Examples of Bare Assertion

Literature. The bare assertion is common in literature (The play Twelve Angry Men is loaded with fallacies. Juror #3 offers the bare assertion to another juror, number 4, when he says, "Now listen to this man (Juror #4), he knows what he's talking about.")

Expository writing. Often bare assertions are given instead of evidence or support for a point. A student essay might read: "Though some people don't agree that smoking causes cancer, they are wrong and that's all there is to it."

BIAS and Persuasive techniques

What is Bias?

Some ways evidence may be misused in order to persuade…

Bandwagon Appeal (Impressing with large numbers)

Assumes that “if everybody’s doing it, it must be good/ right/ okay”

Examples of bandwagon appeal:“McDonald’s Hamburgers, billions sold”Have you seen Spiderman III? The lines at

the theatre are a block long! It must be really good!

Remember, everybody does it is the opposite of thinking for yourself.

Critical thinkers think for themselves!

Appeal to tradition

Argues “this is how it has been done in the past” as a reason for why something should continue to be done

Irrelevant Appeals to authority

An arguer claims he/ she is knowledgeable enough in a subject to make a judgment, but actually is not.

Often used in advertising

Examples of irrelevant appeals to authority:Actresses selling cosmeticsAn Olympic athlete selling an over-

the-counter or prescription drugBob Dole as spokesperson for Viagra

Appeal to Ignorance

Arguer claims something has been proven based on a lack of evidence disproving it.

Examples of appeals to ignorance:You can’t prove that other forms of life don’t

exist in the universe. Therefore, other forms of life must exist in the universe.

And here’s a sensitive issue….Nobody has proven that Clarence has not

been stealing churros from the concession stand. Therefore, Clarence must be stealing churros.