Critical Thinking/Ethics

Relevance of Premises and Fallacies

Relevance of Premises

• We describe the premises of an argument in terms of how much evidence they provide to the truth or falsity of the conclusion.

–Relevance is a matter of degree.

• Some premises are more or less relevant than others

• The more evidence a premise provides to the truth or falsity of the conclusion, the more relevant it is.

Fallacies

• A Fallacy is a category of bad argument that has been identified and is a common mistake or misuse of logic.

–These are bad arguments that are so common they’ve been given names for easy reference and identification

Types of Deductive Arguments & Related

Fallacies

• Denying a Disjunct

• Fallacy: False Dichotomy

• Modus Ponens

• Fallacy: Denying the Antecedent

• Modus Tollens

• Fallacy: Affirming the Consequent

• Tri-Conditional

Disjunctions and Conditionals

• Disjunctions are statements of the form “Either…or…”

• The two propositions on either side of the ‘or’ are called the disjuncts.

• Conditionals are statements of the form “If…then…”

• What comes after the ‘if’ and before the ‘then’ is called the antecedent. What comes after the ‘then’ is called the consequent.

Denying a Disjunct

(1) I will have apples or cheese for lunch today.

(2) I will not have cheese for lunch.

Therefore

(3) I will have apples for lunch.

(1) Either we have free will or it makes little sense to punish criminals for their wrongs.

(2) We don’t have free will.

Therefore

(3) It makes little sense to punish criminals for their wrongs.

(1)S1 or S2 (or both)

(2)Not S1

Therefore

(3) S2

Fallacy: False Dichotomy

• The Fallacy of False Dichotomy occurs when a premise of an argument with a disjunction is false because there are other alternatives besides the two presented in the premise.

• This is a failure of the truth of the premises rather than a failure of form.

Example

(1)She either has an MA in Philosophy, or an MFA in Creative Writing.

(2)She doesn’t have an MFA in Creative Writing.

Therefore,

(3) She has an MA in Philosophy.

Evaluate this argument using the Proper Form and True Premise tests.

Modus Ponens

• 1) If today is Sunday, then we don’t have class.

• 2) Today is Sunday.

Therefore

• 3) We don’t have class.

(1) If S1, then S2.(2) S1.Therefore,(3) S2.

Fallacy: Denying the Antecedent

• 1) If President Obama is a French citizen, then he is a human being.

• 2) President Obama is not a French citizen.

Therefore

• 3) President Obama is not a human being.

(1) If S1, then S2.(2) Not S1.Therefore,(3) Not S2.

• 1) If she’s not in the garage, then she’s in the garden.

• 2) She’s in the garage.

Therefore

• 3) She’s not in the garden.

Denying the Consequent

• 1) If there is fire in here, there is oxygen in here.

• 2) There is no oxygen in here.

Therefore

• 3) There is no fire in here.

(1) If S1, then S2.(2) Not S2.Therefore,(3) Not S1.

• 1) If killing is always wrong, then war is never justified.

• 2) Sometimes war is justified.

Therefore

• 3) Killing isn’t always wrong.

Fallacy: Affirming the Consequent

• 1) If I have the flu, then I have a fever.

• 2) I have a fever.

Therefore

• 3) I have the flu.

(1) If S1, then S2.(2) S2.Therefore,(3) S1.

• 1) If you get an A, then you must have gotten a B on all the quizzes.

• 2) You got a B on all the quizzes.

Therefore

• 3) You’ll get an A.

Tri-Conditionals• 1) If Jules shoots

Butch, Butch will die.

• 2) If Butch dies, Marcellus will be happy.

Therefore

• 3) If Jules shoots Butch, Marcellus will be happy.

(1) If S1, then S2.(2) If S2, then S3.Therefore,(3) If S1, then S3.

Standardizing and Evaluating

• That’s either Mozart or Bach. It can’t be Bach because there’s an electric guitar. It must be Mozart.

• Provided that you complete all the homework assignments on time and get at least a 75% average on all the quizzes and tests, you’ll end up with a B in the course. You didn’t complete all the homework assignments on time. So, you won’t get a B in the course.

Identify the Argument Kind• My mother once told me that either I go to

college or I’d end up with a low-paying job at McDonald’s. I went to Harvard. Hence, I won’t end up with a low-paying job at McDonald’s.

• If you get an A in the course then you must have gotten at least a B on the final exam. You got a B on the final exam. Therefore, you got an A in the course.

• Either you pay me the money or I’ll break your face. You didn’t pay me the money. So, I’m going to break your face.

More Fallacies…

• Remember, fallacies are bad arguments.

Non Sequitur• An argument that contains a premise

or premises that are irrelevant to the conclusion is sometimes said to contain a “non sequitur.“

– “Non sequitur” is Latin for “it doesn’t follow.”

• Remember that relevance can be a matter of degree.

– The premise of an argument can be more or less relevant to its conclusion.

– The more support a premise provides for a conclusion, the more relevant it is to the conclusion.

– Example: People like to put their feet in the sand when they go to the beach. Therefore, putting sand in people’s homes is a good idea.

Fallacy: Easy Target

• The Easy Target Fallacy occurs in three steps

– someone makes an inaccurate claim about the views held by someone else

– the person argues that the inaccurately described view is false

– the person asserts that this argument shows that the accurate view is false

• This is also called the Straw Man Fallacy

Easy Target Fallacy1) S2, a distorted version of S1, is false.Therefore,2) S1 is false.

Suppose Carson makes the following argument:1) Foods that are high in fat and sugar lead are a contributory cause to childhood obesity.2) Reducing childhood obesity is beneficial to society.Therefore,3) School lunches should be made with less fat and less sugar.

Then, suppose Jen attempts a refutation of Carson’s argument with the following:1) If the government decided what people could eat, we wouldn’t be able to have a hot dog at the ball park or buttery popcorn at the movies.2) We should be able to have a hot dog at the ball park and buttery popcorn at the movies.Therefore,3) The government shouldn’t decide what people can eat.Therefore, 4) School lunches shouldn’t be made with less fat and less sugar.

Fallacy: Appeal to Popularity

• The Appeal to Popularity Fallacy occurs when someone argues that a view is true on the grounds that it’s popular

–The fact that most people approve or believe something doesn’t mean that it’s true.

Appeal to Popularity1) Most people approve of or believe S.Therefore,2) S is true. Example:

1) 99.9% of Americans believe the President of the United States is a terrorist.Therefore,2) Barack Obama is a terrorist.

Example 2:1) Billions of people across the globe enjoy smoking cigarettes.Therefore,2) Smoking must be healthy.

In the media: "My fellow Americans...there has been some talk that the government is overstepping its bounds by allowing police to enter peoples' homes without the warrants traditionally required by the Constitution. However, these are dangerous times and dangerous times require appropriate actions. I have in my office thousands of letters from people who let me know…that they heartily endorse the war against crime in these United States. Because of this overwhelming approval, it is evident that the police are doing the right thing."

Fallacy: Appeal to Novelty or Tradition

• The fallacy of Appeal to Novelty or Tradition occurs when someone argues that a statement is true because people have either believed it for a short time (novelty) or for a long time (tradition).

– Things are not automatically true because they have been believed for a long or short period of time

Appeal to Tradition

Example:1) Marriage has for a long time been defined as a commitment made between a man and a woman.Therefore,2) We should not allow homosexuals to marry.

1) S has been believed/done by people for a short/long time.Therefore,2) S is true/we should S.

Consider another example: pretend this argument was being delivered by a mid-19th-century bigot:1) Our country has prospered for nearly a century now and African Americans haven’t been able to vote all along.Therefore,2) African Americans shouldn’t be allowed to vote.

Fallacy: Ad Hominem

• A person commits the Ad Hominem Fallacy when someone attacks a person instead of arguing against the view the person asserts.

–Never use the person who is arguing as a basis for an attack on the argument, or to support it.

–The moment you do, you are committing this fallacy.

Ad Hominem1) H asserts statement S.2) There is something objectionable about Person H.Therefore,3) H’s arguments for S are bad arguments.

In other words: “Your argument is bad because YOU SUCK!”

Example:“President Clinton’s foreign policy is misguided. I mean, just look at howmuch of a scumbag the guy is. He cheated on his wife with an unpaid summer intern at the White House. Obviously, his views on sending troops to Iraq are false.”

Ad Hominems occur ALL THE TIME in the political arena.

Fallacy: Guilt by Association

• The Fallacy of Guilt by Association is a form of the Ad Hominem Fallacy.

– occurs when people are attacked based on their association with a person, group or view that’s considered objectionable

• For example

– If you asserted that a view is false because it was held by someone who interviewed terrorists, you’d be committing the Fallacy of Guilt by Association.

Fallacy of Guilt by Association

“Barack Obama’s economic policy must be awful. Some online sources provide evidence that Obama is a Muslim. Osama Bin Laden was also a Muslim and look at what he did to our country.”

“Mitt Romney can’t be trusted. The guy is a Mormon, which means he literally believes that God came down from heaven in the early 19th century and handed a man named Joe a couple golden plates that gave instructions to humanity for living the good life.

Fallacy: Appeal to Ignorance

• The fallacy of Appeal to Ignorance is committed when a statement is claimed to be true because it hasn’t been shown to be false.

–In an Appeal to Ignorance the evidence being offered in the premises is actually the lack of evidence.

Appeal to Ignorance1) It has not been shown that S is false.Therefore,2) S is true. Example 1:

1) Science has not proven that God doesn’t exist.Therefore,2) God exists.

Example 2:1) Science has not proven that God exists.Therefore,2) God does not exist.

Example 3:“Since no one has been able to prove Iraq doesn’t have weapons of mass destruction, we can conclude that Iraq must have them.”

Fallacy: Begging the Question

• The Fallacy of Begging the Question occurs when the premise of an argument is the same as the conclusion of an argument.

– Note that the “question” in question here is not an interrogative, but rather the topic at hand - the thing the argument is trying to support.

Begging the Question1) S.Therefore,2) S.

Example:“When an abortion occurs, one person, the pregnant woman, has killed an innocent person without any justification. Therefore, abortion is a type of murder.”

Example 2:1) When two people marry, a man and a woman commit to each other for a lifetime.2) Marriage between two gay people is not a commitment between a man and a woman.Therefore,3) Gay marriage is not marriage.

The Naturalistic Fallacy

• The Naturalistic Fallacy occurs when someone confuses what is the case for what ought to be the case.

• Examples:

“Animals kill and eat each other in the wild, so we’re justified in killing and eating them.”

“Being gay just isn’t natural. So it’s wrong.”

Red Herring

• A Red Herring is something that misleads or distracts from a relevant or important issue.

Example: Billy: How could the universe be 6000 years old when we know the speed of light, the distance of astronomical objects (13+ billion light years away), and the fact that the light has reached us[1]?

Marty: 6000 years is not a firm number.  The universe can be as old as about 10,000 years.

Billy: How do you figure that?...

• Explanation: Marty has succeeded in avoiding the devastating question by introducing a new topic for debate... shifting the young-earth creation timeline where it does not necessarily coincide with the Bible.

Appeal to Fear

• An Appeal to Fear occurs when fear, not evidence or reason, is being used as the primary motivator to get others to accept an idea, proposition, or conclusion.

•Example: Logical Form:

1) If you don’t believe X, something terrible will happen to you.

2) Therefore, X must be true.