Cheat sheet

LSAT Logical Reasoning Cheat Sheet

Core Argument Tasks

51%of exam

AssumptionFlawStrengthenWeakenCausation

Inference + Method

20%of exam

InferenceMethodAnalogyEvidenceConclusion

Formal Matching

8%of exam

ParallelConditionalQuantifiersContrapositiveStructure

Other LR Tasks

21%of exam

PrincipleRolePoint at IssueParadoxEvaluate

Quick Facts

Administrator
LSAC
Sections
Two scored LR
Time
35 min each
Questions
Varies, about 24-26
Score
120-180 overall
Standalone Pass
Not published
Official Weights
Not published
Unscored
LR or RC
Format
Short arguments

Assumption Tests

Negate necessary; bridge sufficient

Necessary: must holdSufficient: enough proofGap: missing link

Necessary vs Sufficient

Necessary

  • Required by argument
  • Fails if false
  • Often modest

Sufficient

  • Proves conclusion
  • May be strong
  • Closes gap

Needed vs enough

Attack Picker

  1. Conclusion adds termBridge(Connect terms)
  2. Cause from correlationAlternate cause(Weakens)
  3. Survey supports allSample check(Represent)
  4. Analogy supports resultDifference check(Relevant)
  5. Plan predicts outcomeFeasibility check(Can work)
  6. Expert supports claimAuthority check(Relevant field)
  7. Percent hides totalNumber check(Base rate)
  8. Before-after proofControl check(Other changes)

Assumption Tasks

Necessary
Required link
Sufficient
Guarantees conclusion
Bridge
Connects terms
Defender
Blocks threat
Negation
Tests necessity
Gap
Missing support
New term
Bridge likely

Causal Weakening

Cause? check alternate, reverse, third

Alternate causeReverse causeCoincidenceNo control

Strengthen vs Weaken

Strengthen

  • Supports link
  • May be partial
  • Helps conclusion

Weaken

  • Attacks link
  • May be partial
  • Hurts conclusion

Help vs hurt

Strengthen + Weaken

Strengthen
Helps gap
Weaken
Hurts gap
Alternative cause
Weakens cause
Controls
Strengthen cause
Counterexample
Weakens generalization
Representative sample
Strengthens survey
No difference
Strengthens comparison
Relevant difference
Weakens analogy

Flaw vs Weaken

Flaw

  • Labels error
  • Stimulus flawed
  • No new fact

Weaken

  • Adds fact
  • Damages support
  • Conclusion less likely

Describe vs attack

Flaw Patterns

Causation
Correlation leap
Sampling
Unrepresentative base
Equivocation
Meaning shift
Circularity
Assumes conclusion
Ad hominem
Attacks source
False choice
Missing options
Composition
Parts to whole
Division
Whole to parts
Reversal
Converse error
Negation
Inverse error

Conclusion Test

Because supports; therefore concludes

Because: premiseTherefore: conclusionBut: contrast

MBT vs MSS

MBT

  • Strictly follows
  • No outside assumptions
  • Often weak

MSS

  • Best supported
  • Can be probable
  • Still text-bound

Forced vs supported

Argument Roles

Premise
Support claim
Conclusion
Main claim
Intermediate
Supported support
Background
Context only
Concession
Admitted opposing point
Objection
Counterposition
Example
Illustration
Indicator
Direction cue

Method vs Role

Method

  • Whole argument
  • Reasoning pattern
  • Neutral description

Role

  • Specific statement
  • Premise/conclusion job
  • Local function

Whole vs part

Inference Tasks

MBT
Must follow
MSS
Best supported
Cannot infer
Outside support
Quantifier
Scope limiter
Causal claim
Needs support
Comparison
Same basis needed

Method Tasks

Method
Describes move
Principle
General rule
Analogy
Similar case
Counterexample
Refutes generalization
Elimination
Removes alternatives
Application
Rule to case
Explanation
Accounts for facts

Parallel Filters

Match force, direction, count

ForceDirectionTermsConclusion

Parallel vs Parallel Flaw

Parallel

  • Same structure
  • May be valid
  • Abstract terms

Parallel Flaw

  • Same error
  • Invalid structure
  • Ignore topic

Pattern vs error

Formal Logic Picker

  1. If P then QP then Q(Trigger)
  2. Given not QInfer not P(Valid)
  3. Given Q onlyNo inference(Converse)
  4. Given not PNo inference(Inverse)
  5. Only if appearsNecessary side(After phrase)
  6. Unless appearsNegate trigger(Other required)
  7. Most plus mostSome overlap(Shared base)
  8. Some appearsAt least one(No most)

Conditional Logic

Sufficient
Triggers rule
Necessary
Required result
Contrapositive
Reverse and negate
Only if
Necessary marker
If
Sufficient marker
Unless
Negate trigger
Some
At least one
Most
More than half
All
Every member

Quantifier Ladder

All > most > some

All: everyMost: over halfSome: at least one

Parallel Tasks

Validity
Match valid/flawed
Structure
Same skeleton
Quantifiers
Same force
Polarity
Match positive/negative
Terms
Same count
Conclusion
Same strength
Direction
Same conditionals

Principle Identify vs Apply

Identify

  • Find rule
  • Justifies argument
  • Generalizes facts

Apply

  • Use rule
  • Match conditions
  • Draw consequence

Choose vs use

Stem Picker

  1. Find required assumptionNecessary(Negate)
  2. Guarantee conclusionSufficient(Bridge gap)
  3. Make conclusion strongerStrengthen(Help link)
  4. Make conclusion weakerWeaken(Attack link)
  5. Describe reasoning errorFlaw(Name mistake)
  6. Explain surprising factsParadox(Both true)
  7. Find shared disputePoint at issue(Both speakers)
  8. Judge useful informationEvaluate(Test gap)

Other Tasks

Main conclusion
Primary claim
Role
Statement function
Point at issue
Shared disagreement
Paradox
Coexistence explanation
Evaluate
Tests assumption
Principle apply
Rule's consequence
Principle identify
Justifying rule
Agree/disagree
Speaker stance

Issue vs Paradox

Point at issue

  • Two speakers
  • Same claim
  • Opposite stances

Paradox

  • Two facts
  • Both accepted
  • Needs explanation

Dispute vs coexist

Common Traps

True but irrelevant

True statement Wrong task

Outside assumptions

Text supports World knowledge distracts

Causal shortcut

Correlation shown Cause not proven

Reversed conditionals

P triggers Q Q proves nothing

Stronger conclusion

Evidence modest Answer overclaims

Similar topic

Topic matches Structure differs

One speaker only

One addresses claim Other stays silent

Paradox denial

Facts stand Answer explains both

Last Minute

  1. 1.Find conclusion first
  2. 2.Name task before choices
  3. 3.Premises are accepted
  4. 4.Assumptions bridge gaps
  5. 5.Necessary? negate answer
  6. 6.Sufficient? prove conclusion
  7. 7.Weaken attacks support
  8. 8.Strengthen helps support
  9. 9.MBT avoids outside assumptions
  10. 10.Parallel ignores subject matter
  11. 11.Flaw labels bad reasoning
  12. 12.Paradox keeps both facts
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