-
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 Argument-Type 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.*
|
|
