The most basic logic rule is the Conditional (which is a phrase in the form of A → B).

1. Followers:

If A, then B.

If James competes, then Macro must go to the race as a coach.

The item on the left in an If… then… statement is called the Sufficient, and the item on the right is the Necessary. The LSAT buries these conditionals in convoluted language. They are rarely stated bluntly as “if… then….

We can diagram conditionals by abbreviating the necessary and sufficient phrases and then using an arrow (→) to join them.

[sufficient condition][necessary condition]

Conditionals Video Summary

  • 00:24 – Mastering conditional logic is important for passing the LSAT since 38% of the Logical Reasoning questions use conditional statements or conditional logic.
  • 00:52 – A conditional statement is in the form of X → Y.
  • 1:08 – The left side of the conditional statement is the sufficient condition and the right side the necessary condition.
  • 2:15 – Solving causal arguments involves putting the statements into the form of a conditional statement (X → Y).
  • 4:20 – The conditional statements in the Logical Reasoning section may take the form of a syllogism:
    If A → B, and B → C, then A → C.
  • 5:10 – LSAT questions revolve around taking away one of the parts of this syllogism and asking you to find it.

“If you can dream it,
you can do it.”
-Walt Disney

DREAM → DO

“A person is not old until they let regrets
take the place of their dreams.”
John Barrymore

O → LRTPD

1. SUFFICIENT CONDITIONS

Now, we are going to delve into the specifics of how to identify necessary and sufficient conditions and diagram conditional statements on the LSAT.

Sufficient Conditions Video Summary

  • 0:23 – The sufficient condition is the one on the left side of a conditional statement (if-then relationship).
  • 0:53 – Language cues or indicator words are terms used to recognize whether a condition is a sufficient one or a necessary one.
  • 2:07 – The sufficient indicators help us determine a sufficient condition. These keywords are listed on the LSAT Sufficient Indicators sub-section.
  • 2:24 – For example: The dog barks every time someone knocks on the door. The sufficient indicator keyword “every” helps us determine the sufficient condition “. . . someone knocks on the door.
  • 2:52 – Diagram the statement where “. . . someone knocks on the door” (K) is on the left side of the conditional while “The dog barks . . .” (B) is on the right side. The diagram becomes: K → B.
  • 2:58 – Another example: Whoever is kind is loved. The keyword “whoever” tells us that the sufficient condition is the phrase “. . . is kind . . .,” so the necessary condition is the phrase “. . . is loved.
  • 3:44 – Diagram this statement as follows: K → L.
  • 4:02 – Another example: Flowers were the only decorations. The indicator “the only” tells us that “. . . decorations” (D) is the sufficient condition, while “Flowers…” (F) is the necessary condition.
  • 4:25 – Diagram this as: D → F.

LSAT Sufficient Indicators: these are keywords that indicate a sufficient condition.

  • If
  • If only
  • All
  • Any
  • Each
  • Every
  • When
  • Whenever
  • Whoever
  • Whatever
  • Whenever
  • People who
  • In order
  • Any

1a. Diagram Sufficient Conditionals

Sufficient indicator phrases like if… then or when are straightforward to diagram. They use the basic structure:
sufficient indicator [sufficient] → [necessary]

Diagram: When your cell phone rings in a theater, people will glare at you.

1. Locate the sufficient indicator (This will help tell you what the sufficient condition is.): When your cell phone rings in a theater, people will glare at you.

2. Locate the conditional phrase after the sufficient indicator: When your cell phone rings in a theater . . .” (This phrase is the sufficient conditionthe first part of the conditional.)

3. Abbreviate it: PRT (phone rings theater)

4. Locate the necessary result in the conditional:  “. . . people will glare at you. (This is the necessary conditionthe second part of the conditional.)

5. Abbreviate it: PGY (people glare you)

6. Join these two conditions into a sufficientnecessary diagram:

PRTPGY

Next LSAT: January 13th

1b. Sufficient: Each, If, Every, Any

If every member of a group has a trait, you can diagram the conditional in the form: (group [sufficient]) (trait [necessary]).

All A’s are B’s is the same thing as A → B.

All dogs are mammals.

2. Locate the phrase after the sufficient indicator

“. . . dogs . . .” (The phrase after the sufficient indicator is the sufficient condition.)

Abbreviate the sufficient condition: D

3. Locate the necessary condition

“. . . are mammals.” (The phrase other than the sufficient condition is the necessary condition.)

Abbreviate the necessary condition: M

4. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

D → M

Every person who has gone to Yosemite remembers it.

2. Locate the phrase after the sufficient indicator

“. . . person who has gone to Yosemite . . .” (The phrase after the sufficient indicator is the sufficient condition.)

Abbreviate the sufficient condition: GTY

3. Locate the necessary condition

“. . . remembers it.” (The phrase other than the sufficient condition is the necessary condition.)

Abbreviate the necessary condition: RI

4. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

GTY → RI

Whenever I speak to my boss I get nervous.

2. Locate the phrase after the sufficient indicator

“. . . I speak to my boss . . .” (The phrase after the sufficient indicator is the sufficient condition.)

Abbreviate the sufficient condition: STB

3. Locate the necessary condition

“. . . I get nervous.” (The phrase other than the sufficient condition is the necessary condition.)

Abbreviate the necessary condition: GN

4. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

STB → GN

Every LSAT student wants to master formal logic.

2. Locate the phrase after the sufficient indicator

. . . LSAT student . . .” (The phrase after the sufficient indicator is the sufficient condition.)

Abbreviate the sufficient condition: LS

3. Locate the necessary condition

. . . wants to master formal logic.” (The phrase other than the sufficient condition is the necessary condition.)

Abbreviate the necessary condition: WMFL

4. Final conditional

Combine the two conditions in the form of: sufficient → necessary

LS → WMFL

1c. Sufficient: No / None

Meet the tilde: ~

A tilde (~) and a slash both symbolize a negation or inversion. In this course, we use both the tilde and the slash because you’ll see both versions in LSAT courses. For statements that use the conditional indicators no/none, we put the tilde on the necessary condition.

None of the canned jellybeans are purple.

2. Locate the phrase after the sufficient indicator

. . . of the canned jellybeans . . .” (The phrase after the sufficient indicator is the sufficient condition.)

Abbreviate the sufficient condition: CJ

3. Locate the necessary condition

. . . are purple.” (The phrase other than the sufficient condition is the necessary condition.)

Abbreviate the necessary condition: P

4. Negate the necessary condition

Using the sufficient indicator “none” means negating the necessary condition using a tilde (~): ~(P) = ~P

5. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

CJ →  ~P

No human has stepped foot on Mars.

2. Locate the phrase after the sufficient indicator

. . . human . . .” (The phrase after the sufficient indicator is the sufficient condition.)

Abbreviate the sufficient condition: H

3. Locate the necessary condition

. . . has stepped foot on Mars.” (The phrase other than the sufficient condition is the necessary condition.)

Abbreviate the necessary condition: SFM

4. Negate the necessary condition

Using the sufficient indicator “no” means negating the necessary condition using a tilde (~): ~(SFM) = ~SFM

5. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

H →  ~SFM

No great white sharks are vegetarians.

2. Locate the phrase after the sufficient indicator

. . . great white sharks . . .” (The phrase after the sufficient indicator is the sufficient condition.)

Abbreviate the sufficient condition: GW

3. Locate the necessary condition

. . . are vegetarians.” (The phrase other than the sufficient condition is the necessary condition.)

Abbreviate the sufficient condition: V

4. Negate the necessary condition

Using the sufficient indicator “none” means negating the necessary condition using a tilde (~): ~(V) = ~V

5. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

GWS →  ~V

1d. Sufficient: Never

If you can’t beat them, join them.

2. Locate the phrase after the sufficient indicator

. . . you can’t beat them . . .” (The phrase after the sufficient indicator is the sufficient condition.)

Abbreviate the sufficient condition: ~B

3. Locate the necessary condition

. . . join them.” (The phrase other than the sufficient condition is the necessary condition.)

Abbreviate the necessary condition: J

4. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

~B → J

If you can count your money, you don’t have a billion dollars.

-J. Paul Getty

2. Locate the phrase after the sufficient indicator

. . . you can count your money . . .” (The phrase after the sufficient indicator is the sufficient condition.)

Abbreviate the sufficient condition: CYM

3. Locate the necessary condition

. . . you don’t have a billion dollars.” (The phrase other than the sufficient condition is the necessary condition.)

Abbreviate the necessary condition: ~B

4. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

CYM → ~B

2. NECESSARY CONDITIONS

Necessary Conditions Video Summary

  • 0:24 – The necessary condition is on the right side of a conditional statement (if-then relationship).
  • 1:38 – Note: Avoid reversing the direction of conditional statements because they are not equivalent statements.
  • 1:50 – There are keywords that help you identify necessary conditions. These are called necessary indicators and they are listed on the LSAT Necessary Indicators sub-section.
  • 2:02 – For example: Only if Liam goes to the movie premiere will Lily go. The keywords “only if” tells us that the phrase “. . . Liam goes to the movie premiere . . .” is the necessary condition, so the phrase “. . . will Lily go.” is the sufficient condition.
  • 2:34 – Note: In cases where the words start with the same letter, use the whole words when diagramming to avoid confusion.
  • 3:04 – Diagram the conditional statement as follows: Lily → Liam.
  • 3:10 – For example: A successful landing on Mars depends on entering the atmosphere at 14°. The necessary indicator “depends on” tells us that the phrase “. . . entering the atmosphere at 14°” (14°) is the necessary condition, while the phrase “A successful landing on Mars . . .” (SL) is the sufficient condition. We can diagram this as: SL → 14°.
  • 3:50 – Another example: You don’t deserve praise for something unless you did it deliberately.
  • 3:56 – The keyword “unless” gives us the necessary condition “. . . you did it deliberately” (D), but it also requires us to apply a negation to the sufficient condition. It belongs to a set of unique keywords that functions similarly with others such as “until” and “except”. The sufficient condition is “You don’t deserve praise for something . . .” (~P).
  • 4:44 – Diagram this as follows: ~(~P) → D; simplify as P →D.

LSAT Necessary Indicators
sufficient → [necessary indicator] necessary
Only
Only if
Only when
Relies on
Depends on
Must
Requires

See at 3:56 in the video:
~sufficient → [necessary indicator] necessary
(When these necessary indicators are used, you also have to negate the sufficient condition.)
Unless
Until
Except

2a. Diagram Necessary Conditionals

To finish a marathon you must run 26 miles.

 [sufficient] → necessary indicator [necessary]

1. Locate the necessary indicator: To finish a marathon you must run 26 miles.

2. Locate the necessary phrase after the necessary indicator: “. . . must run 26 miles. (This phrase is the necessary conditionthe second part of the conditional.)

3. Abbreviate it: R26 (run 26)

4. Locate the sufficient in the conditional: “To finish a marathon . . .(This phrase is the sufficient conditionthe first part of the conditional.)

5. Abbreviate it: FM (finish marathon)

6. Join these two conditions into a sufficientnecessary diagram:

FMR26

Unless you run 26 miles, you can’t finish a marathon.

~[sufficient] → necessary indicator [necessary]

Note that unless, except, and until require a negation of the sufficient as explained in video above (4:26).

1. Locate the necessary indicator: Unless you run 26 miles . . .

2. Locate the necessary phrase after the necessary indicator: Unless you run 26 miles . . . (This phrase is the necessary conditionthe second part of the conditional.)

3. Abbreviate it: R26 (run 26)

4. Locate the sufficient in the conditional:  “. . . you can’t finish a marathon. (This phrase is the sufficient conditionthe first part of the conditional.)

5. Abbreviate it: ~FM (can’t finish marathon)

6. Since we are using unless, we must negate the sufficient condition using a tilde (~): ~(~FM) = FM (note: the double negatives cancel out)

7. Join these two conditions into a sufficientnecessary diagram:

FM → R26

2b. Necessary: Only / Only If

Only indicates the necessary condition (the second item in the conditional).

Only coffee can get Ricky up in the morning.

2. Locate the phrase after the necessary indicator

. . . coffee . . .” (The phrase after the necessary indicator is the necessary condition.)

Abbreviate the necessary condition: C

3. Locate the sufficient condition

. . . get Ricky up in the morning.” (The phrase other than the necessary condition is the sufficient condition.)

Abbreviate the sufficient condition: RUM

4. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

RUM → C

Only dogs bark at vacuum cleaners. 

2. Locate the phrase after the necessary indicator

“. . . dogs . . .” (The phrase after the necessary indicator is the necessary condition.)

Abbreviate the necessary condition: D

3. Locate the sufficient condition

. . . bark at vacuum cleaners.” (The phrase other than the necessary condition is the sufficient condition.)

Abbreviate the sufficient condition: BVC

4. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

BVC → D

It is only the ignorant who despise education.

-Publilius Syrus

2. Locate the phrase after the necessary indicator

. . . the ignorant . . .” (The phrase after the necessary indicator is the necessary condition.)

Abbreviate the necessary condition: I

3. Locate the sufficient condition

. . . who despise education.” (The phrase other than the necessary condition is the sufficient condition.)

Abbreviate the sufficient condition: DE

4. Final conditional

Combine the two conditions in the form of: sufficient → necessary

DE → I

The only truth is music.

-Jack Kerouac

2. Locate the phrase after the necessary indicator

. . . truth . . .” (The phrase after the necessary indicator is the necessary condition.)

Abbreviate the necessary condition: T

3. Locate the sufficient condition

. . . is music.” (The phrase other than the necessary condition is the sufficient condition.)

Abbreviate the sufficient condition: M

4. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

M → T

2c. Examples

You can use the funds in my other bank account only in cases of emergency.

1. Locate the keyword indicator

Only (necessary indicator)

2. Locate the phrase after the keyword indicator

. . . in cases of emergency.” (This is the necessary condition.)

Abbreviate the necessary condition: CE

3. Locate the other conditional phrase

You can use the funds in my other bank account . . .” (This phrase is the sufficient condition.)

Abbreviate the sufficient condition: UFBA

4. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

UFBA → CE

Going to another country requires having a passport.

1. Locate the keyword indicator

requires (necessary indicator)

2. Locate the phrase after the keyword indicator

. . . having a passport.” (This phrase is the necessary condition.)

Abbreviate the necessary condition: HP

3. Locate the other conditional phrase

Going to another country . . .” (This phrase is the sufficient condition.)

Abbreviate the sufficient condition: GAC

4. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

GAC → HP

The candidate who I will vote for depends on my political leanings.

1. Locate the keyword indicator

depends on (necessary indicator)

2. Locate the phrase after the keyword indicator

. . . political leanings.” (This phrase is the necessary condition.)

Abbreviate the necessary condition: PL

3. Locate the other conditional phrase

The candidate who I will vote for . . .” (This phrase is the sufficient condition.)

Abbreviate the sufficient condition: CIV

4. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

CIV → PL

The company won’t reconnect their service unless you pay the overdue bill.

1. Locate the keyword indicator

unless (necessary indicator)

2. Locate the phrase after the keyword indicator

. . . you pay the overdue bill.” (This phrase is the necessary condition.)

Abbreviate the necessary condition: POB

3. Locate the other conditional phrase

The company won’t reconnect their service . . .” (This phrase is the sufficient condition.)

Abbreviate the sufficient condition: ~CRS

4. Negate the sufficient condition

Using the necessary indicator “unless” means negating the sufficient condition using a tilde (~): ~(~CRS) = CRS

5. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

CRS → POB

I may be able to attend the party only if they announce the date and time asap.

1. Locate the keyword indicator

only if (necessary indicator)

2. Locate the phrase after the keyword indicator

. . . they announce the date and time asap.” (This phrase is the necessary condition.)

Abbreviate the necessary condition: ADT

3. Locate the other conditional phrase

I may able to attend the party . . .” (This phrase is the sufficient condition.)

Abbreviate the sufficient condition: AP

4. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

AP → ADT

Every student taking a master’s degree has a bachelor’s degree.

1. Locate the keyword indicator

Every (sufficient indicator)

2. Locate the phrase after the keyword indicator

. . . student taking a master’s degree . . .” (This phrase is the sufficient condition.)

Abbreviate the sufficient condition: TMD

3. Locate the other conditional phrase

. . . has a bachelor’s degree . . .” (This phrase is the necessary condition.)

Abbreviate the necessary condition: HBD

4. Final Conditional

Combine the two conditions in the form of: sufficient → necessary

TMD → HBD

2d. Examples from famous quotes

“Whenever people agree with me I always feel I must be wrong.”

-Oscar Wilde

1. Locate the keyword indicator

Whenever (sufficient indicator)

2. Locate the phrase after the keyword indicator

“. . . people agree with me . . .” (This is the sufficient condition.)

Abbreviate the sufficient condition: PA

3. Locate the other conditional phrase

“. . . I always feel I must be wrong.” (This phrase is the necessary condition.)

Abbreviate the necessary condition: FW

4. Final Conditional

Combine the two conditions in the form: sufficient → necessary

PA → FW

“When you have eliminated the impossible, whatever remains, however improbable, must be the truth.”

-Sherlock Holmes

1. Locate the keyword indicator

When (sufficient indicator)

2. Locate the phrase after the keyword indicator

“. . . you have eliminated the impossible . . .” (This is the sufficient condition.)

Abbreviate the sufficient condition: EI

3. Locate the other conditional phrase

“. . . whatever remains, however improbable, must be the truth.” (This phrase is the necessary condition.)

Abbreviate the necessary condition: RT

4. Final Conditional

Combine the two conditions in the form: sufficient → necessary

EI → RT

“If you tell the truth, you don’t have to remember anything.”

-Mark Twain

1. Locate the keyword indicator

If (sufficient condition)

2. Locate the phrase after the keyword indicator

“. . . you tell the truth . . .” (This is the sufficient condition.)

Abbreviate the sufficient condition: TT

3. Locate the other conditional phrase

“. . . you don’t have to remember anything.” (This phrase is the necessary condition.)

Abbreviate the necessary condition: ~RM (“. . . do not have to remember anything . . .”)

4. Final Conditional

Combine the two conditions in the form: sufficient → necessary

TT → ~RM

“I can resist everything except temptation.”

-Oscar Wilde

1. Locate the keyword indicator

except (necessary indicator)

2. Locate the phrase after the keyword indicator

“. . . temptation.” (This is the necessary condition.)

Abbreviate the necessary condition: T

3. Locate the other conditional phrase

“I can resist everything . . .” (This phrase is the sufficient condition.)

Abbreviate the necessary condition: RE

4. Negate the sufficient condition

Using the necessary indicator “except” means we have to negate the sufficient condition using at tilde (~): ~(RE) = ~RE

5. Final Conditional

Combine the two conditions in the form: sufficient → necessary

~RE → T

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Next LSAT: January 13th