LOGICAL FALLACIES

Errors in Reasoning

LOGIC

The science of how to evaluate arguments and The science of how to evaluate arguments and reasoningreasoning

Logic allows us to distinguish correct reasoning Logic allows us to distinguish correct reasoning from poor reasoningfrom poor reasoning

Logic helps us to reason correctlyLogic helps us to reason correctly

FALLACY (noun)

A failure in reasoning that makes an argument A failure in reasoning that makes an argument invalidinvalid

Fallacious (adjective) *wrong, untrue, inaccurate, Fallacious (adjective) *wrong, untrue, inaccurate, flawed flawed

WHAT IS AN ARGUMENT?

A connected series of statements intended to A connected series of statements intended to establish a definite assertionestablish a definite assertion

An argument is never made up of a simple An argument is never made up of a simple statement!statement!

An argument needs to offer reasons and An argument needs to offer reasons and evidence for the purpose of establishing the evidence for the purpose of establishing the truth.truth.

Argument cont.

Made of 3 parts: Made of 3 parts:

A) A) a claim/assertion a claim/assertion – the position statement – the position statement that can be proven true or falsethat can be proven true or false

B) a warrant – the statement after the claim, B) a warrant – the statement after the claim, that is used to support it or demonstrate that is used to support it or demonstrate evidence for itevidence for it

C) a conclusion – the final assertion in the C) a conclusion – the final assertion in the argumentargument

Ad Hoc

When you make up a defense to your argument When you make up a defense to your argument that does not really make sense for the counter that does not really make sense for the counter argument you have just been givenargument you have just been given

EX:EX:

CLAIM: That boy likes me.CLAIM: That boy likes me.

But, he has a girlfriend.But, he has a girlfriend.

WARRANT: He has a girlfriend and he is only dating WARRANT: He has a girlfriend and he is only dating her to make me jealous. her to make me jealous.

Ad Hominem

When you attack the character of the person When you attack the character of the person making the claimmaking the claim

EX: EX:

CLAIM: Sally says that people should never kill CLAIM: Sally says that people should never kill animals for food. animals for food.

WARRANT: Well, Sally is a sissy crybaby that loves WARRANT: Well, Sally is a sissy crybaby that loves animals too much. animals too much.

Hasty Generalization

When you use an idea based on a small When you use an idea based on a small sample of a larger populationsample of a larger population

EX: EX:

CLAIM: All short students are really smart. CLAIM: All short students are really smart.

WARRANT: All of the short students in my class WARRANT: All of the short students in my class are getting As in every subject.are getting As in every subject.

Slanting

When you emphasize one side of the evidence When you emphasize one side of the evidence (usually the favorable info)(usually the favorable info)

EX:EX:

CLAIM: Polar bears are not becoming extinct.CLAIM: Polar bears are not becoming extinct.

WARRANT: The number of polar bears in this WARRANT: The number of polar bears in this small Alaskan town has reached record high small Alaskan town has reached record high numbers. numbers.

Begging the Question

When you make the assumption that something is When you make the assumption that something is correct because something else is correctcorrect because something else is correct

EX: EX:

CLAIM: These rules are important and must be CLAIM: These rules are important and must be followed. followed.

WARRANT: If these rules were not important enough to WARRANT: If these rules were not important enough to be followed, then no one would have invented be followed, then no one would have invented them. them.

Straw Man

When you misrepresent an argument to make When you misrepresent an argument to make it easier to attackit easier to attack

EX:EX:

CLAIM: You want our country to be taken over. CLAIM: You want our country to be taken over.

WARRANT: You said you believe that our WARRANT: You said you believe that our country should spend more money on country should spend more money on education. This means that you want the education. This means that you want the military to suffer.military to suffer.

Slippery Slope

When you say that if A happens, then Z will When you say that if A happens, then Z will definitely happen. Therefore, A should not happen.definitely happen. Therefore, A should not happen.

EX: EX:

CLAIM: Students should have homework even on CLAIM: Students should have homework even on the weekends. the weekends.

WARRANTL: Students that do not complete weekend WARRANTL: Students that do not complete weekend homework become lazy and unmotivated. homework become lazy and unmotivated.

Post Hoc Ergo Propter Hoc (Post Hoc)

When you assume that because something When you assume that because something occurred before another, the first caused the occurred before another, the first caused the secondsecond

(After this, therefore, because of this)(After this, therefore, because of this)

EX: EX:

CLAIM: This charm made me do well on my tests. CLAIM: This charm made me do well on my tests.

WARRANT: After I bought the charm, I did well on a WARRANT: After I bought the charm, I did well on a test. test.

False Analogy

When you make a comparison of two things When you make a comparison of two things which is inaccuratewhich is inaccurate

EX:EX:CLAIM: Women are like delicate flowers. CLAIM: Women are like delicate flowers.

WARRANT: Women, like flowers, must be cut WARRANT: Women, like flowers, must be cut from their foundations and placed into crystal from their foundations and placed into crystal vases. vases.

Red Herring

When you introduce a totally different topic in order When you introduce a totally different topic in order to take attention away from the real argumentto take attention away from the real argument

EX: EX:

CLAIM: Hunting must be outlawed to preserve CLAIM: Hunting must be outlawed to preserve wildlife in California. wildlife in California.

WARRANT: Hunting causes thousands of accidents WARRANT: Hunting causes thousands of accidents every year that takes the lives of young children.every year that takes the lives of young children.

Questionable Cause

The idea that if 2 things always occur The idea that if 2 things always occur together, then 1 must cause the othertogether, then 1 must cause the other

EX: EX:

CLAIM: Rap music causes violence.CLAIM: Rap music causes violence.

WARRANT: ever since rap became popular, WARRANT: ever since rap became popular, kids have become more violent. kids have become more violent.

Appeal to the Consequences of a Belief

Something is true because if it were not, then Something is true because if it were not, then there would be negative consequencesthere would be negative consequences

Also known as Wishful thinkingAlso known as Wishful thinking

EX: EX:

CLAIM: Unicorns exist.CLAIM: Unicorns exist.

WARRANT: Unicorns exist, because if they did not, WARRANT: Unicorns exist, because if they did not, millions of children would be very sad.millions of children would be very sad.

Appeal to Authority

Using an “expert” to prove a claimUsing an “expert” to prove a claim

• EX: EX:

• CLAIM: One Direction is the best boy band CLAIM: One Direction is the best boy band ever. ever.

• WARRANT: My little sister, Mary, is obsessed WARRANT: My little sister, Mary, is obsessed with all boy bands and she says that One with all boy bands and she says that One Direction is the best!Direction is the best!

Appeal to Common Practice• The idea that ‘everyone’ does something and that The idea that ‘everyone’ does something and that

makes it okaymakes it okay

• EX: EX:

• CLAIM: At St. Anthony’s, I donCLAIM: At St. Anthony’s, I don’’t have to tuck in my t have to tuck in my shirt. shirt.

• WARRANT: I know I donWARRANT: I know I don’’t have to tuck in my shirt, t have to tuck in my shirt, because most of the kids in my class don’t tuck because most of the kids in my class don’t tuck theirs in. theirs in.

Appeal to Emotion

• The idea that something feels good and that The idea that something feels good and that makes it okay to domakes it okay to do

• EX: EX:

• CLAIM: Drinking Gatorade makes you feel CLAIM: Drinking Gatorade makes you feel good. good.

• WARRANT: Drinking Gatorade will make you a WARRANT: Drinking Gatorade will make you a better athlete because it makes you feel better athlete because it makes you feel stronger and faster. stronger and faster.

Appeal to Fear

• The idea that if something scares you, you The idea that if something scares you, you should not do itshould not do it

• EX: EX:

• CLAIM: Children should never be taught to CLAIM: Children should never be taught to use a stove.use a stove.

• WARRANT: Children that use stoves will WARRANT: Children that use stoves will definitely burn themselves. definitely burn themselves.

Appeal to Flattery

• The idea that a compliment makes something rightThe idea that a compliment makes something right

• EX: EX:

• CLAIM: Mr. Brown, you are the best teacher ever!CLAIM: Mr. Brown, you are the best teacher ever!

• WARRANT: Mr. Brown should totally give us extra WARRANT: Mr. Brown should totally give us extra points because we think he is the best.points because we think he is the best.

Appeal to Tradition/Appeal to Novelty• The idea that all old or The idea that all old or

new things are always new things are always betterbetter

• EX: EX:

• CLAIM: This restaurant CLAIM: This restaurant is the best. is the best.

• WARRANT: My family WARRANT: My family has been eating here has been eating here for five generations! for five generations!

• EX: EX:

• CLAIM: This restaurant CLAIM: This restaurant is really good. is really good.

• WARRANT: I heard they WARRANT: I heard they use this new cooking use this new cooking technology that does technology that does not even use heat to not even use heat to cook the food. cook the food.

Burden of Proof

• The introduction of a claim that the other side The introduction of a claim that the other side must provemust prove

• EX: EX:

• CLAIM: Unicorns exist. CLAIM: Unicorns exist.

• WARRANT: You cannot prove that unicorns do WARRANT: You cannot prove that unicorns do not exist, so they must be real.not exist, so they must be real.

QUIZ TIME!