Critical ThinkingCritical Thinking

““The Art of Reasoning The Art of Reasoning Well”Well”

Critical ThinkingCritical Thinking

Reasoning Well Involves Reasoning Well Involves ArgumentsArguments

Argument Argument does notdoes not mean a mean a verbal verbal disputedispute

An Argument Is A Series Of An Argument Is A Series Of Statements, Called Statements, Called Premises, Leading To A Premises, Leading To A ConclusionConclusion

ArgumentsArguments

Logic:Logic: The study of the formal principles of reasoning

ArgumentsArguments

Deductive Deductive ArgumentArgument:: the the truth of the truth of the premises premises guarantees the guarantees the truth of the truth of the conclusionconclusion

Inductive Inductive ArgumentArgument:: the the truth of the truth of the premises makes premises makes the truth of the the truth of the conclusion more conclusion more probable probable

Deductive ArgumentsDeductive Arguments

Example (Valid):Example (Valid): 1. If it snows, then 1. If it snows, then

it is cold (premise) it is cold (premise) 2. It snows 2. It snows

(premise) (premise) 3. Therefore, it is 3. Therefore, it is

cold (conclusion) cold (conclusion)

VALID DEDUCTIVE VALID DEDUCTIVE ARGUMENTARGUMENT:: The The argument is in the argument is in the proper formproper form

Deductive ArgumentsDeductive Arguments

Example (Invalid):Example (Invalid): 1. If it snows, then it 1. If it snows, then it

is cold (premise) is cold (premise) 2. It is cold 2. It is cold

(premise) (premise) 3. Therefore, it 3. Therefore, it

snows (conclusion)snows (conclusion)

Deductive ArgumentsDeductive Arguments INVALID INVALID :: The The

argument is not in the argument is not in the proper form.proper form.

Informal  testing for Informal  testing for deductive validity: deductive validity:

Can You Think of a Can You Think of a counter example?counter example?

If yes, the argument is If yes, the argument is invalid.invalid.

Deductive ArgumentsDeductive Arguments

If Tom Cruise is a If Tom Cruise is a bulldog then he bulldog then he has four legs has four legs (Premise) (Premise)

Tom Cruise is a Tom Cruise is a bulldog (Premise) bulldog (Premise)

Therefore, Tom Therefore, Tom Cruise has four Cruise has four legs (Conclusion) legs (Conclusion)

Is the Argument Valid?Is the Argument Valid?

Have we proven that Have we proven that Tom Cruise has four Tom Cruise has four legs?legs?

Deductive ArgumentsDeductive Arguments

If it is determined that the argument If it is determined that the argument is is validvalid it must next be determined it must next be determined if the argument is if the argument is soundsound..

A sound argument is A sound argument is valid valid argument with argument with true premisestrue premises..

Deductive ArgumentsDeductive Arguments

If Tom Cruise is a If Tom Cruise is a bulldog then he has bulldog then he has four legsfour legs

Tom Cruise is a Tom Cruise is a bulldogbulldog

Therefore Tom Therefore Tom Cruise has four legsCruise has four legs

Is the Argument Is the Argument Sound?Sound?

Inductive ArgumentsInductive Arguments

Examples:Examples:

1.All observed emeralds have been found to be green 1.All observed emeralds have been found to be green 2.Therefore, the next observed emerald will be green. 2.Therefore, the next observed emerald will be green.

1.In the past, sugar cubes have dissolved in water 1.In the past, sugar cubes have dissolved in water 2.Thus, this sugar cube will dissolve in water. 2.Thus, this sugar cube will dissolve in water.

1. 70% of BCCC students in the sample are from Bristol 1. 70% of BCCC students in the sample are from Bristol 2. Hence, 70% of BCCC students are from Bristol 2. Hence, 70% of BCCC students are from Bristol

Unstated PremisesUnstated Premises Many times Many times

arguments have arguments have one or more one or more unstated unstated premises that premises that need to be added need to be added to support the to support the conclusion.conclusion.

Sally’s dog is a Sally’s dog is a bloodhound therefore it bloodhound therefore it has a keen sense of has a keen sense of smellsmell

Unstated PremisesUnstated Premises It is February, so I will It is February, so I will

dress warmlydress warmly Drugs should not be Drugs should not be

legalizedlegalized

Analyzing ArgumentsAnalyzing Arguments

Reconstruct the ArgumentReconstruct the Argument

1. Find the conclusion. 1. Find the conclusion.

2. Find the premises 2. Find the premises

3. Find any unstated premises 3. Find any unstated premises

““The glove doesn’t fit so you The glove doesn’t fit so you must acquit”must acquit”

Conclusion:Conclusion:

Defendant should be acquittedDefendant should be acquitted Premise(s):Premise(s):

The glove doesn't fit the defendant The glove doesn't fit the defendant (premise - stated) (premise - stated)

Unstated premises:Unstated premises:

If evidence does not fit the If evidence does not fit the defendant, then the defendant should defendant, then the defendant should be acquitted (premise - unstated) be acquitted (premise - unstated)

The glove is evidence (premise - The glove is evidence (premise - unstated) unstated)

Analyzing ArgumentsAnalyzing Arguments

Evaluate the argumentEvaluate the argument

1. Is the argument valid? 1. Is the argument valid? (Can I think of a counter (Can I think of a counter example?)example?)

2. Are the premises true? 2. Are the premises true?

Evaluating the ArgumentEvaluating the Argument

1. Is the argument 1. Is the argument valid? valid?

(Can I think of a (Can I think of a counter counter example?)example?)

2. Are the premises 2. Are the premises true?true?

– If evidence does not If evidence does not fit the defendant, then fit the defendant, then the defendant should the defendant should be acquittedbe acquitted

– The glove is evidence The glove is evidence – The glove doesn't fit The glove doesn't fit

the defendant the defendant – Therefore, defendant Therefore, defendant

should be acquittedshould be acquitted

Logical FallaciesLogical Fallacies

Mistakes in logic when presenting our Mistakes in logic when presenting our arguments.arguments.

Formal Fallacy: An invalid argumentFormal Fallacy: An invalid argument

Informal Fallacy: Type of bad reasoning Informal Fallacy: Type of bad reasoning that can only be detected by examining the that can only be detected by examining the content of the argumentcontent of the argument..

Informal FallaciesInformal Fallacies

Begging the Begging the QuestionQuestion

Assuming what you Assuming what you are trying to proveare trying to prove

“ “Capital punishment Capital punishment is wrong because it is is wrong because it is immoral”immoral”

Informal FallaciesInformal Fallacies

Ad Hominem AttackAd Hominem Attack Attack on your Attack on your

opponent rather that opponent rather that his or her argumenthis or her argument

““The only reason that The only reason that you think Capital you think Capital punishment is wrong is punishment is wrong is because you are a because you are a bleeding heart liberal”bleeding heart liberal”

Informal FallaciesInformal Fallacies

Red Herring:Red Herring:

Sidetracking the Sidetracking the argument with an argument with an irrelevant issueirrelevant issue

““Honda makes the Honda makes the best cars” --- “No they best cars” --- “No they don’t their workers are don’t their workers are treated poorly”treated poorly”

Informal FallaciesInformal Fallacies

Hasty Generalization:Hasty Generalization:

Drawing general Drawing general conclusions from a conclusions from a small samplesmall sample

““A number of A number of professional athletes have professional athletes have been convicted of crimes been convicted of crimes therefore all professional therefore all professional athletes are criminals”athletes are criminals”

ArgumentsArguments George bush is a good George bush is a good

presidentpresident George Bush is a bad George Bush is a bad

presidentpresident