# LSAT Lesson 1

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1. Components of a Logical Reasoning Question
• 1. Stimulus
• 2. Question Stem
2. 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. 3 Steps to Evaluate an Argument-Type Stimulus
• 1. Determine premises
• 2. Determine conclusion
• 3. Evaluate conclusion (i.e., determine validity of conclusion)
4. 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*

5. 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*
6. Assumption
Unstated Premise

*Assumptions strengthen arguments

Type II Question: Strengthen/Assumption/Premise
7. 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]."
8. Structural Indicators: Premises
• *Because
• *Since

• -For
• -After all
• -It can be proven by the fact that
9. Structural Indicators: Conclusions
• Therefore
• Consequently
• Thus
• Hence
• So
• It follows that
• It can be concluded that
10. 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
11. 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
12. 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
13. 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
14. 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
15. Type I Logical Reasoning Question
Must be true/Conclusion/Inference

*13.7% of LR Questions*
16. Type II Logical Reasoning Question
Strengthen/Premise/Assumption

Answer Choice (Premise) supports Stimulus (Conclusion)

*27% of LR Questions*
17. Type III Logical Reasoning Question
Weaken/Undermine

Answer Choice (Statement) weakens Stimulus (Conclusion)

*10.5% of LR Questions*
18. 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
19. 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
20. No Formula
Introduces sufficient condition. Negate other part of statement for the necessary condition.

No cat barks.

C ---> B

*None
21. 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
22. Not Both Formula
One variable is the sufficent. Negate the other for the necessary.

She cannot run and walk at the same time.

• R ---> W
• W ---> R

*Implies that at least one of two variables must be absent"*

*Both variables can be absent*

23. 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
24. Either/Or Rule
Negate one part for the sufficient. Other part is necessary.

Either she eats, or she dies.

• E ---> D
• D ---> E

*Implies at least one variable must be present.*

*Can have both.*
 Author: apwu ID: 231386 Card Set: LSAT Lesson 1 Updated: 2013-08-26 15:27:03 Tags: Logical Reasoning Logic Games Folders: Description: Lesson 1 Show Answers: