The most basic logic rule is the Conditional (which is just a phrase like A → B). We can diagram conditionals by abbreviating them and then using an arrow (→) to join the statements.

1. Followers:

If A, then B.

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

1. SUFFICIENT CONDITIONS

Now were going to delve into the specifics of how to identify necessary and sufficient conditions on the LSAT and then diagram them.

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: 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]…. (that phrase is the sufficient conditionthe first part).

3. Abbreviate it: PRT (phone rings theater)

4. Locate the necessary “result” in the conditional:  …[people will glare at you] (that’s the necessary conditionthe second part).

5. Abbreviate it: PGY (people glare you)

6. Put abbreviations into a sufficientnecessary diagram: PRTPGY

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

If every member of a group has a trait, then you can just do (group [sufficient]) (trait [necessary]).

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

All dogs are mammals

D → M

Every person who has gone to Yosemite remembers it.

GTY → RI

Whenever I speak to my boss I get nervous.

STB → GN

Every LSAT student wants to master formal logic.

LS → WMFL

1c. Sufficient: No / None

Meet the tilde: ~

That squiggly line (~) or a slash through symbolizes the opposite or an inversion. In this course, we use both the tilde and the slash because you’ll see both versions in LSAT courses. For no/none, we put the tilde on the necessary condition.

No human has stepped foot on Mars.

Diagram of Quote

H →  ~SFM
(SFM symbolizes “stepped foot on Mars.”)

None of the canned jellybeans are purple.

Diagram of Quote

CJs →  ~P
(CJ abbreviates “canned jellybeans.”)

No Great White Sharks are vegetarians.

Diagram of Quote

GWS →  ~V
(GWS abbreviates “Great White Shark.”)

1d. Sufficient: Never

You’ll typically use the ~ symbol in “never” statements on the necessary condition.

“If you can’t beat them, join them.”

“If you can count your money,
you don’t have a billion dollars.”
-J. Paul Getty

2. NECESSARY CONDITIONS

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

See at 4:25 in the video:
~sufficient → [nec. indicator] necessary
(when you build this you have to put a tilde in front of the sufficient).
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]. (that phrase is the necessary conditionthe second part of the diagram).

3. Abbreviate it: R26 (run 26)

4. Locate the sufficient in the conditional:  …[To finish a marathon.] (that’s the sufficient conditionthe first part of the diagram).

5. Abbreviate it: FM (finish marathon)

6. Put abbreviations 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]. (that phrase is the necessary conditionthe second part of the diagram).

3. Abbreviate it: R26 (run 26)

4. Locate the sufficient in the conditional:  …[you can’t finish a marathon.] (that’s the sufficient conditionthe first part of the diagram).

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

6. Since we are using, we put a tilde in front of it: ~(~FM) note: the double negatives cancel out.

7. Put abbreviations 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.

Ricky up → coffee

Only dogs bark at vacuum cleaners. 

bark at vacuum cleaner → dog

“It is only the ignorant
who despise education.”
-Publilius Syrus

Diagram of Quote

Despise education → Ignorant
DE → I

“The only truth is music.”
-Jack Kerouac

Diagram of Quote

Truth → Music
T → M

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Next LSAT: September 21st