BEING LOGICAL: The Sources of Illogical Thinking

Reminders
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
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Sound Argument
Relies on content and structure
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Statements are true or false Arguments are valid or invalid

Types of Argument
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 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.

Types of Argument
Conditional Argument If A then B If Flora is running, then Flora is moving. A, therefore B Flora is running, therefore Flora is moving. 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.

Types of Argument
Syllogistic Argument Every M is P. Every S is M. Therefore every S is P.

M P

Remember
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.

Relevant Premises
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.

Quality of Premises
Quality refers to whether a statement is affirmative or negative. When a conclusion is negative, at least one of the premises must negative No Americans are Canadian. Everyone from Washington is American. Therefore, no one from Washington is Canadian.

Quality of Premises
All affirmative premisesEveryone from Washington is American. I am from Washington. Therefore, I am not American. All negative premisesNo Canadians are American. No one from Washington is Canadian. Therefore no one from Washington is American.

Constructing an Argument
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 an argument

skepticism
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
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Evasive Agnosticism
If I am agnostic, what do I believe? Agnosticism = uncertainty Evasive Agnosticism is using agnosticism as an excuse Saying I don't know without trying to find out the answer It's okay to be uncertain, but we should not use this as an excuse for not trying
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Cynicism and nave Optimism

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

Narrow-Mindedness
Not open to other ideas, weak-sense critical thinking, refusing to consider alternatives that don't agree with your own prejudices
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Example: looking for your keys The solution: Open-mindedness?

In Class Reflection
To tolerate everything is to value nothing. What do you think of this statement? Do you agree or disagree? Why?
The object of opening the mind, as of opening the mouth, is to shut it again on something solid. ~G.K. Chesterton

BEING LOGICAL: The Principle Forms of Illogical Thinking (Fallacies)

Formal Fallacies
Formal fallacies structure 1. Denying the Antecedent
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If Louise is running, then she is moving. Louise is not running. Therefore, she is not moving.

Formal Fallacies
2. Affirming the Consequent If Louise is running, then she is moving. Louise is moving. Therefore, she is running.
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Formal Fallacies
3. The Undistributed Middle guilt by association Every M is P. Every S is P. Therefore every S is M.

M P

some Nazis were members of the music club. Joe was a member of the music club. Therefore, Joe was a Nazi.

Ad Hominem

Informal Fallacies
Either-Or Appeal to Popularity Searching for a Perfect solution Wishful Thinking Explaining by Naming Glittering Generality Begging the Question

Slippery slope Equivocation

Appeal to Emotion Straw man Appeal to Questionable Authority Red Herring

Informal Fallacies
Of course this mode of government is the best. We have had this government for over 200 years and no one has talked about changing it in all that time. So, it has got to be good.
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Informal Fallacies
Using and Abusing Tradition Things have always been done this way is not a good reason to do them that way
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Can apply to the opposite: it's not a good reason to not do them that way either.

Informal Fallacies
Bill borrows Janes expensive pen and doesnt return it. Jane therefore decides its okay not to return Bills book.
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Informal Fallacies
Two Wrongs Don't Make a Right It's all right to do X because Y has already been done.
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They did it first.

Informal Fallacies
Laughter as a Diversionary Tactic Tears as a Diversionary Tactic What do these both have in common?
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They are actually forms of the Appeal to Emotions fallacy!