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Components of a Logical Reasoning Question
 1. Stimulus
 2. Question Stem
 3. Answer Choices

Types of Stimulus
1. Argument: Conclusion and Premises ISO conclusion
*70% of questions are arguments*
2. Set of Facts: group of statements without conclusion
*Must consciously decide if a question is an argument or set of facts*

3 Steps to Evaluate an ArgumentType Stimulus
 1. Determine premises
 2. Determine conclusion
 3. Evaluate conclusion (i.e., determine validity of conclusion)

Valid Conclusion
A statement that must be true according to the premises.
*80% of LSAT arguments are invalid*
*Soundness (factual accuracy) does not affect answer choices*

Sufficient and Necessary Conditions
Sufficient Condition: what is enough to make something true
Necessary Condition: what is required to make something true
*A sufficient condition is by definition necessary, but not the other way around*
*Negating a necessary condition always negates the sufficient, but not the other way around*

Assumption
Unstated Premise
*Assumptions strengthen arguments
Type II Question: Strengthen/Assumption/Premise

Structural Indicator
Words that create relationships between other words or statements
Arguments do not require structural indicators:
"That movie sucked [C]. The acting was bad [P]."
"(Since) the acting was bad [P], (it follows that the movie sucked [C]."

Structural Indicators: Premises
 For
 After all
 It can be proven by the fact that

Structural Indicators: Conclusions
 Therefore
 Consequently
 Thus
 Hence
 So
 It follows that
 It can be concluded that

Invalid Forms of Argumentation: Incorrect Negation
If it's an apple, then it's a fruit.
A>F
If it's not an apple, then it's not a fruit.
A > F: WRONG

Invalid Forms of Argumentation: Incorrect Reversal
If it's an apple, then it's a fruit.
A>F
If it's a fruit, then it's an apple.
F > A: WRONG

Contrapositive
Correct form of argumentation.
Reverse and negate.
If it's an apple, then it's a fruit.
A > F
If it's not a fruit, then it's not an apple.
F > A

And/Or Rule
To convert to the contrapositive in statements with multiple sufficient or necessary conditions, change all and's to or's and all or's to and's

Breaking Down And/Or Statements
 A > B and C
 ≠
 A > B
 A > C
 A > B or C
 ≠
 A > B
 A > C
 A or B > C
 ≠
 A > C
 A > C
 A and B > C
 ≠
 A > B
 A > C

Type I Logical Reasoning Question
Must be true/Conclusion/Inference
Stimulus (Premises) lead to Answer choice (Conclusion).
*Ask: Did they prove it?
*13.7% of LR Questions*

Type II Logical Reasoning Question
Strengthen/Premise/Assumption
Answer Choice (Premise) supports Stimulus (Conclusion)
*27% of LR Questions*

Type III Logical Reasoning Question
Weaken/Undermine
Answer Choice (Statement) weakens Stimulus (Conclusion)
*10.5% of LR Questions*

If Formula
"If" introduces the sufficient condition.
If it's an apple, then it's a fruit.
A > F
I won't play again if he keeps hogging the ball.
HB > P
 *When, Whenever, As long as
 *Where, Wherever

All Formula
"All" introduces the sufficient condition.
All dogs bark.
D > B
*Each, every*
Any at the beginning of a sentence has the same meaning.
"Any bird has feathers" = B > F
"Would any of you like cake?" NOT SAME

No Formula
Introduces sufficient condition. Negate other part of statement for the necessary condition.
No cat barks.
C > B
*None

Only If Formula
"Only if" introduces the necessary condition.
"You can enter the club only if you have a membership."
EC > HM
"Only if you drive will I come to the movies."
CM > YD
*Only by itself refers to the necessary condition, but does not necessarily introduce it.
*Only if/when/where introduce the necessary.
*"The only" introduces the sufficient condition.
"The only fruits are apples."
F > A
"Only fruits are apples."
A > F

Not Both Formula
One variable is the sufficent. Negate the other for the necessary.
She cannot run and walk at the same time.
* Implies that at least one of two variables must be absent"*
*Both variables can be absent*

Unless Formula
"Unless" introduces the necessary condition. Negate the other part for the sufficient."
We will lose unless we play like a team.
L > PT
Unless we get air support, this mission will fail.
F > GAS
*"Not...unless" = "Only if"*
Only if we get air support can the mission succeed.
MS > GAS
The mission cannot succeed unless we get air support.
MS > GAS

Either/Or Rule
Negate one part for the sufficient. Other part is necessary.
Either she eats, or she dies.
*Implies at least one variable must be present.*
* Can have both.*

