Eng 111Eng 111

Dana FriersonDana Frierson

Fall 1998Fall 1998

Types of Reasoning (Logic)Types of Reasoning (Logic)

DeductiveDeductive Inferring particular “fact” from general Inferring particular “fact” from general

assumptionsassumptions General to specificGeneral to specific

InductiveInductive Moving from evidence to conclusionsMoving from evidence to conclusions Specific to GeneralSpecific to General

DeductionDeduction Chain of reasoning involving premises and Chain of reasoning involving premises and

conclusionconclusion Three part chain of reasoning: syllogismThree part chain of reasoning: syllogism

All humans are mortal. (major premise)All humans are mortal. (major premise) Socrates is a human. (minor premise)Socrates is a human. (minor premise) Socrates is mortal. (Conclusion)Socrates is mortal. (Conclusion)

InductionInduction

Based on fair Based on fair sample of sample of evidenceevidence

You taste 30 You taste 30 green apples.green apples.

Each one is sour.Each one is sour. You generalize You generalize

that green apples that green apples are sour.are sour.

Fallacious ReasoningFallacious Reasoning Error in logicError in logic Often designed to Often designed to

trick or fool trick or fool audienceaudience

Sometimes, used Sometimes, used unintentionallyunintentionally

Avoid them in your Avoid them in your argumentargument

Common fallaciesCommon fallacies

Non Sequitur: Conclusion does not Non Sequitur: Conclusion does not logically follow its premiselogically follow its premise Jones will make a good senator Jones will make a good senator

because he is a man.because he is a man. Post hoc: Claim there is a cause-effect Post hoc: Claim there is a cause-effect

relationship when there is not.relationship when there is not. SuperstitionsSuperstitions

Common FallaciesCommon Fallacies Allness: Imply that something is true for Allness: Imply that something is true for

an entire class or groupan entire class or group Daughters have a special bond with Daughters have a special bond with

their mothers.their mothers. Begging the Question: Say the same thing Begging the Question: Say the same thing

in different words.in different words. Abortion is murder because it is the Abortion is murder because it is the

intentional killing of a human beingintentional killing of a human being..

Common FallaciesCommon Fallacies Either/Or: State that there are only two Either/Or: State that there are only two

alternativesalternatives America, love it or leave it!America, love it or leave it! If you think education is expensive, try If you think education is expensive, try

ignorance. ignorance. Faulty Authority: “authority” lacks Faulty Authority: “authority” lacks

credibility or expertise to support claimcredibility or expertise to support claim Most commercials that use celebrities!Most commercials that use celebrities!

Common Fallacies-DistractionsCommon Fallacies-Distractions Ad Hominem: Ad Hominem:

attack the character attack the character of opponentof opponent

How dare How dare Congressman Smith Congressman Smith advocate population advocate population control when he has control when he has six children?six children?

Red Herring: Red Herring: Divert attention by Divert attention by irrelevant issueirrelevant issue

What difference What difference does it make does it make whether Clinton is whether Clinton is guilty of perjury guilty of perjury when the economy is when the economy is doing so well? doing so well?

Fallacies, Cont.Fallacies, Cont.

False Analogy: two cases are not False Analogy: two cases are not sufficiently parallel.sufficiently parallel. Johnny Cochran’s analogy Johnny Cochran’s analogy

Bandwagon: Appeal to people’s urge Bandwagon: Appeal to people’s urge to belongto belong ““Wouldn’t you like to be a pepper Wouldn’t you like to be a pepper

too?”too?”

Fallacies, Cont.Fallacies, Cont.

Slippery Slope: If we take one step, it Slippery Slope: If we take one step, it will lead to extremewill lead to extreme If I make an exception for you; I have If I make an exception for you; I have

to make an exception for everyone.to make an exception for everyone. Loaded Question: Question will cast Loaded Question: Question will cast

guilt no matter how opponent responds.guilt no matter how opponent responds. When did you stop abusing your wife?When did you stop abusing your wife?

Name that fallacy!Name that fallacy!

Employees are like nails. Just as nails must Employees are like nails. Just as nails must be hit in the head in order to make them be hit in the head in order to make them work, so must employees.work, so must employees.

False AnalogyFalse Analogy

Name that Fallacy!Name that Fallacy!

Chicken soup Chicken soup cures colds. I ate cures colds. I ate some chicken some chicken soup and two soup and two days later, my days later, my cold disappeared.cold disappeared.

Post HocPost Hoc

Name that Fallacy!Name that Fallacy!

If guns are outlawed, only outlaws will have If guns are outlawed, only outlaws will have guns.guns.

Slippery SlopeSlippery Slope

The Bible is true because it is inspired by God.

The Bible is true because it is inspired by God.

Begging the questionBegging the question

Name that Fallacy!Name that Fallacy!

All wars are not wrong. The people who All wars are not wrong. The people who say so are cowards.say so are cowards.

Ad HominemAd Hominem

Essay AssignmentEssay Assignment Read EssayRead Essay As you read, note As you read, note

errors in reasoning.errors in reasoning. Try to label Try to label

fallacies, if you can.fallacies, if you can. Don’t be surprised Don’t be surprised

when I call on you when I call on you to share your to share your discoveries!discoveries!

Final Draft Due Tuesday!Final Draft Due Tuesday!