Critical Thinking

By Ms Cheryl

Withaneachi

What is a GoodArgument?

By Ms Cheryl

Withaneachi

Learning Content

LearningObjective (L3.0)

By Ms Cheryl Withaneachi

Important Definitions

Keywords

0 Plausible Claims0 Begging theQuestion0 Valid argument0 Invalid argument0 Strong arguments0 Weak arguments

0 Conclusion thatfollows frompremises

the

By Ms Cheryl Withaneachi

Good Reason to Believe

0What makes an argumentgood?

By Ms Cheryl Withaneachi

Good arguments?0 Is it that it should convince someone?0 Who? Me, you?0 What if the person you are convincing is

sleepy, in a bad mood etc?

What is a Good Argument?0The premise gives a good reasonto believe the conclusion is true.

0What is good reason though?

Things to Remember!

Things to rememberIf we believe the premise, then there is a good reason for us to believe the conclusion right? So if we can’t find a reason to believe the premise then we won’t have a good reason to believe the conclusion.

Example:

False premise, false conclusionAll books are written by

woman[P1]So the author of this book is a wom

an [C].

0 False premise, true conclusionAll books are written by women [P2].So the author of this book is a human

being.[C]

Things to remember

False premise, false conclusionAll books are written by

woman[P1]So the author of this book is a wom

an [C].

False premise, true conclusionAll books are written by women [P2].So the author of this book is a human

being.[C]

Let’s Try This Ourselves:

False premise, false conclusion………………………………[P1]

……………………………………….[C].

False premise, true conclusion………………………………. [P2].

………………………………………….[C]

Plausible Claim

0 A claim is plausible[probable/possible] ifgood reason to believe it is true.

we have

It is less plausible, the less reason we have to believe itis true.

It is implausible or dubious if we have no reason tobelieve it its true.

Plausible Claim0 A claim is plausible[probable/possible] ifgood reason to believe it is true.

Let’s Test this theoryA claim is plausible/possible if we have a good reason

to believe it’s true;All good people go to heaven [P1]

So my brother will go to heaven[C]Let’s Analyze

If you have a good reason to believe the concept of heaven and hell, and that good people go to heaven, it is

likely the conclusion is true right?

we have

Plausible Claim

It is less plausible, the less reason we have to believe itis true. Let’s Test this theory

A claim is less plausible/not possible if we have a less reason to believe it’s true;

All aliens are intelligent beings that live in Mars[P1]So all intelligent beings are in Mars[C]

Let’s AnalyzeIf you have less reason to believe the fact that aliens

exists and that there are intelligent beings, is it likely that the conclusion is true or false??

Plausible Claim

It is implausible or dubious if we have no reason tobelieve it its true.

Let’s Test this theoryA claim is implausible/not possible at all if we have a no

reason to believe it’s true;All happy feet penguins fly everyday. [P1]

So all happy feet penguins can fly[C]Let’s Analyze

If you have NO reason to believe the fact that happy penguins fly everyday, would the conclusion be true or

false??

But is plausible enough?

0 Sometimes it is not, we will explore this furtherThat True?0 Even if you agree the premise is plausible

in Is

(possible/probable),conclusion.

it’s less plausible than the

Begging the Question0 An argument begs the question of one of

itsis no more plausible than the conclusion.

premises

0 This is bad (for any argument).

Begging the QuestionIs when the person arguing believes in truth of the conclusion

or presents is as one of the premises. But this is not sufficient because the premise should provide truth of the conclusion, not state the conclusion.

We should believe god exists because of the bible says he exists. And we should believe what the bible says because

it is the word of god.Analysis:

1. Supports each conclusion using another conclusion.2. Does not mean the ideas are not true but there is no

independent evidence for the statement given.3. It goes in circles, not really giving a solid reason.

By Ms Cheryl Withaneachi

Begging the Question

Why is abortion wrong? Because all murder is wrong.

Analyze!

By Ms Cheryl Withaneachi

Conclusion Follows fromPremise

Does this have plausible premises?

the

Dr.E teaches critical thinking.So Dr. E is bald

Analysis:The conclusion does not

follow the premises.The premises do not lead to, support or establish

conclusion.

the

0What is the bestconnection between

premises andconclusion?

Remember!

0 If there is no possibility that both the premise couldbe true and the conclusion false, then if the premiseare true, the conclusion has to be true too;

0 Every student at this school has paid tuition.0 Suzy is a student at this school.0 So Suzy has paid tuition.

wise.

Premises0 So if we have a good reason to believe that every student at this school has paid tuition, and also that Suzy is a student at this school, then we have a good

reasonother

to believe she has paid tuition- it couldn’t be

What is a Valid Argument?0 An argument is valid if the premise is true and the conclusion is true at the same time. Because there is no way that the premise could be true and the conclusion false at the same time.

A valid argumentgood.

need not be

Premise0 Every elected official in the US is under thirty-fouryears old.0 So

theold.

President of the US is under thirty-four years

Analysis:

0 This argument is valid. When the premise is true,there is no way the conclusion can be false even if thelaws change.

0 But if laws changed, and its prohibits people older than 34 from holding office, then it would be

impossible for the president to be older than0 But the argument is bad, since it has a false conclusion- because the premise is false.

34.

Some validargumentsbad.

are

Is every argument valid?

0 Danny heard this morning that parrot were on sale atthe mall. He knows his neighbor has a birdcage andwonder if it would be big enough.

Analysis

0 All parrot anyone I know has ever seen, or heard, or readabout are under 2 feet tall.0 Therefore all parrots on sale at the male are under 2 feet tall.

0 Premise could be true even if there is a possibility that theconclusion is false.0 The conclusion does follow from the premise, even thoughthe argument is not valid or less valid.

Strong & WeakArguments

0 An argument is strong if there is some way (chances are high)- premise is true even if its conclusion is false- although that is unlikely..0 An argument is weak, if its possible and not unlikely for its premises to be true, and its conclusion false (at the same time)

Weak/Bad Arguments

0Dick is a student.0So Dick doesn’t drive a motorcycle.

The conclusion follows fromthe premise means that theargument is valid or strong

How to evaluate anargument?

0 Imagine the possibilities.1. Every good argument is valid or strong.2. Not every valid or strong argument is good

premise could be implausible)(a

3. Only invalid arguments are classifiedweak.4. Every weak argument is bad.

from strong to

In any of these ways is the

conclusion false?

YES: VALIDHOW

LIKELY?NO= VALIDEVERY WAY THE PREMISES COULD BE TRUETHE CONCLUSION IS TRUE

VERYUNLIKELY: STRONG

NOT SOUNLIKELY: WEAK

Test for anArgument to be Good

0 What are the three tests?1. The premises are plausible.

2. The premises are more plausible conclusion.

than the

3. The argument is valid or strong.

Conditions:

0 Why do we evaluate if we don’t knowpremises are true?

0 Think house loan. Do you know if thestate is actually true?

whether the

income they

0 Each of this tests is independent of the others.0 Each can fail while the other two hold.

0 We can start with which is easier to determine.

0 Are the arguments valid? If not, whereon

the

the scale from strong to weak, doesexample lie? If the argument is valid

or strong, is it also good?

Analysis the following:

0 Dr.E is a philosophy professor.0 All philosophy professors are bald.

0 So Dr. E bald.

Let’s analysis the followingexamples in the nextslides…

few

Analysis

Is the argument valid? Y/N Remember there is no way the premise could be true

and the conclusion false at the same time. If the premise is true, the conclusion is true.

But it isis false.

a bad argument because the second premise

In any of these ways is the

conclusion false?

YES: VALIDHOW

LIKELY?NO= VALIDEVERY WAY THE PREMISES COULD BE TRUETHE CONCLUSION IS TRUE

VERYUNLIKELY: STRONG

NOT SOUNLIKELY: WEAK

0 Maria to her supervisor:

I was told that I would earn a bonus if I put in 100 hoursof overtime and had a perfect attendance record for twomonths. I have since put in 110 hours of overtime andhave a perfect attendance record forSo I’m entitle to a bonus.

the last ten weeks.

Analysis:

0 Is this a valid argument? Y/N0 It’s not possible for the premise to beconclusion false.

true and the

0 But we don’t know if the argument is good because wedon’t know if the premise is true.

0 Danny is a bachelor. So Danny was never married.

0 Is this argument valid? Y/N0 Danny could have been divorced.0 The argument is weak, so given what we know, chance

are that is unlikely the premise is true and theconclusion false. So the argument is bad.

Remember!

An argument is weak, if its possible and not unlikely for its premises to

be true, and its conclusion false (atthethe same time)

How do we show anargument is weak?

We describe at least one likely way in which thepremise could be true and the conclusion false.