LSAT Lesson 1

• 1. Stimulus
• 2. Question Stem
• 3. Answer Choices

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*

• 1. Determine premises
• 2. Determine conclusion
• 3. Evaluate conclusion (i.e., determine validity of 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 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*

Unstated Premise

*Assumptions strengthen arguments

Type II Question: Strengthen/Assumption/Premise

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]."

• *Because
• *Since

• -For
• -After all
• -It can be proven by the fact that

• Therefore
• Consequently
• Thus
• Hence
• So
• It follows that
• It can be concluded that

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

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

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

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

• 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

Must be true/Conclusion/Inference

Stimulus (Premises) lead to Answer choice (Conclusion).

*Ask: Did they prove it?

*13.7% of LR Questions*

Strengthen/Premise/Assumption

Answer Choice (Premise) supports Stimulus (Conclusion)

*27% of LR Questions*

Weaken/Undermine

Answer Choice (Statement) weakens Stimulus (Conclusion)

*10.5% of LR Questions*

"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" 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

Introduces sufficient condition. Negate other part of statement for the necessary condition.

No cat barks.

C ---> B

*None

"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

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*

"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

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.*