being logical 4

8/4/2019 Being Logical 4

http://slidepdf.com/reader/full/being-logical-4 1/27

BEING LOGICAL:BEING LOGICAL:

TheThe SourceSources of Illogicals of IllogicalThinkingThinking



Extra Credit Assignment may be turned in at any

time before finals week

Up Next: Final Exam Review

The Final Exam will be on Monday september

26th from 1:00 p.m. - 4:00 p.m. In PC214

(that's here)

Today: Being Logical Parts 4 and 5

Reminder Reminder ss

s



Relies on content and structure

Statements are true or false

Arguments are valid or invalid

Sound ArgumentSound Argument

s



You don't need to know the names of these, but you

should understand how they work.

Conjunctive Argument – Both A and B are true

A and B, Therefore A

Kimi is a student at Payap University and she is

majoring in business management.

In this type of argument, both A and B must be true!

Types of ArgumentTypes of Argument



Disjunctive Argument – A or B

Denny either took the train to Bangkok or he took the

bus.

Mutually exclusive

Denny took the train, therefore he did not take the bus.

Denny took the bus, therefore he did not take the train.

Denny did not take the train, therefore he took the bus.

Denny did not take the bus, therefore he took the train.




Conditional Argument – If A then B

If Flora is running, then Flora is moving.

A, therefore B → Flora is running, therefore Flora ismoving.

Not B, therefore not A → Flora is not moving, therefore

Flora is not running.

Be careful! Not A, therefore not B is an invalid

argument. → Flora is not running, therefore Flora is

not moving.




Syllogistic Argument – Every M is P.

Every S is M.Therefore every S is P.


S M

P



A true statement and a valid argument are the same

thing!

False premises in a valid argument will create false

conclusions.

Every athlete is a ballet dancer.Ben Franks is an athlete.

Therefore, Ben Franks is a ballet dancer.

Remember Remember



Every member of the All Blacks is very successful.

Ben Franks is a member of the All Blacks.

Therefore, Ben Franks should be elected governor.

Ben Franks is a member of the All Blacks.

Ben Franks is 183 cm tall.

Ben Franks could beat you up.Therefore, Ben Franks should be elected governor.

Relevant PremiRelevant Premisesses



Quality refers to whether a statement is affirmative or

negative.

When a conclusion is negative, at least one of thepremises must negative

No Americans are Canadian.

Everyone from Washington is American.Therefore, no one from Washington is Canadian.

Quality of PremisesQuality of Premises



All affirmative premises-

Everyone from Washington is American.

I am from Washington.

Therefore, I am not American.

All negative premises-

No Canadians are American.

No one from Washington is Canadian.Therefore no one from Washington is American.

Quality of PremisesQuality of Premises



The Truth of Premises – get the facts straight

-if even some of the facts are wrong, the entire

argument will be called into question

The strength of Premises – Only choose the best!

-weed out weaker premises

-fewer premises sharpen the focus of anargument

ConConstructing an Argumentstructing an Argument



Is it good to be skeptical?

Extreme skepticism – There is no truth

Moderate skepticism – There may be truth, but the

human mind cannot grasp it. (In the end, this has the

same result as extreme skepticism)

In critical thinking, skepticism should be selectively

employed → we reserve judgment, but only for a time

skepticismskepticism

s



If I am agnostic, what do I believe?

Agnosticism = uncertainty

Evasive Agnosticism is using agnosticism as anexcuse

Saying “I don't know” without trying to find out the

answer

It's okay to be uncertain, but we should not use thisas an excuse for not trying

Evasive AgnosticismEvasive Agnosticism

s



Cynical – bitterly distrustful, contemptuous, or

pessimistic. (Dictionary.com)

Optimistic - disposed to take a favorable view of events or conditions and to expect the most

favorable outcome. (Dictionary.com)

Opposite points of view that make the same mistake

Prejudiced → pre-judge → judge before knowing the

facts

Blinds us to possibilities, creates self-fulfilling

prophecies or disappointment

Cynicism and naïveCynicism and naïve

OptimismOptimism

s



Not open to other ideas, weak-sense critical thinking,

refusing to consider alternatives that don't agree with

your own prejudices

Example: looking for your keys

The solution: Open-mindedness?

Narrow-Mindedness Narrow-Mindedness

s



To tolerate everything is to valueTo tolerate everything is to value

nothing.nothing.

What do you think of this What do you think of this

statement? Do you agree orstatement? Do you agree or

disagree? Why?disagree? Why?

“The object of opening the mind, as of opening the mouth, is to

shut it again on something solid.” ~G.K. Chesterton

In Class Reflection



BEING LOGICAL:BEING LOGICAL:

The PrincipleThe Principle Forms ofForms ofIllogical ThinkingIllogical Thinking

(Fallacies)(Fallacies)



Formal fallacies – structure

1. Denying the Antecedent

If Louise is running, then she is moving.

Louise is not running.

Therefore, she is not moving.

Formal FallaciesFormal Fallacies

s



2. Affirming the Consequent

If Louise is running, then she is moving.Louise is moving.

Therefore, she is running.

Formal FallaciesFormal Fallacies

s



Every M is P.

Every S is P.Therefore every S is M.

some Nazis were members of the music club.

Joe was a member of the music club.

Therefore, Joe was a Nazi.

Formal FallacieFormal Fallaciess

S M

P

3. The Undistributed Middle → guilt by association



Ad Hominem

Slippery slope

Equivocation

Appeal to Emotion

Straw man

Appeal to Questionable

Authority

Red Herring

Informal FallaciesInformal Fallacies

s

Either-Or

Appeal to Popularity

Searching for a Perfectsolution

Wishful Thinking

Explaining by Naming

Glittering Generality

Begging the Question



Of course this mode of government is the best. We haveOf course this mode of government is the best. We have

had this government for over 200 years and no one hashad this government for over 200 years and no one hastalked about changing it in all that time. So, it has got totalked about changing it in all that time. So, it has got to

be good. be good.


s



Using and Abusing Tradition

“Things have always been done this way” is not a

good reason to do them that way

Can apply to the opposite: it's not a good reason to

not do them that way either.


s



Bill borrows Jane’s expensive pen and doesn’t return it.Bill borrows Jane’s expensive pen and doesn’t return it.Jane therefore decides it’s okay not to return Bill’s book.Jane therefore decides it’s okay not to return Bill’s book.


s



Two Wrongs Don't Make a Right

“It's all right to do X because Y has already beendone.”

They did it first.


s



Laughter as a Diversionary Tactic

Tears as a Diversionary Tactic

What do these both have in common?

They are actually forms of the Appeal to Emotions

fallacy!


s

being logical 4

Documents