SAT Grammar: Boundaries — Punctuation

Master periods, commas, semicolons, colons, dashes, and apostrophes on the SAT Reading & Writing test

Punctuation is a key concept in SAT grammar. Mastery allows you to control meaning, avoid run-ons and fragments, set off extra information, and clarify complex ideas. This guide covers how the SAT tests commas, semicolons, colons, dashes, and apostrophes.

What Is Punctuation?

Definition: Punctuation marks indicate boundaries within and between sentences. They separate ideas, show pauses or emphasis, clarify meaning, and organize information. The right mark depends on grammatical structure—not on how long a pause "feels."

Period (.) — Separates complete sentences (independent clauses).
Comma (,) — Used for lists, extra info (supplements), between adjectives, in dates, after introductions, and with FANBOYS to link clauses.
Semicolon (;) — Links two closely related independent clauses.
Colon (:) — Introduces a list, explanation, or emphasis after a complete sentence.
Dash (—) — Sets off supplements or extra info, or to create an emphatic break.
Apostrophe (') — Shows possession or contractions.

Formulas:

\(\text{Independent clause} . \ \text{Independent clause}\)
\(\text{Independent clause}, \ \text{FANBOYS} \ \text{Independent clause}\)
\(\text{Independent clause}; \ \text{Independent clause}\)
\(\text{Independent clause}: \ \text{list/explanation/emphasis}\)
\(\text{Main clause} \,\,—\,\, \text{non-essential info} \,\,—\,\, \text{rest of main clause}\)

Tip: Punctuation fixes should always be based on sentence structure, not by “how it sounds” when read aloud.

Common SAT Pitfalls & Tips

❌ Comma Splice: Never join two independent clauses with only a comma (I left, she stayed).
❌ Misused Semicolon: Never use ; before “and,” “or,” “but,” etc. (semicolon never combines with FANBOYS).
❌ Colon fragment: A colon must follow a complete sentence, not a fragment.
❌ Lone dash/comma: If you start a supplement or aside, you must close it with matching punctuation.
✅ If stuck, break it into short, declarative sentences. If you can't, re-examine for run-ons or fragments.
✅ Test alternatives by reading without the supplement—should still be grammatically correct.

Fully Worked SAT-Style Examples

Example 1 (Comma vs. Semicolon):

The museum opens at 10 a.m; the first tour begins at 10:30 a.m.

Both clauses are independent so use a semicolon, not a comma.

Example 2 (Comma + FANBOYS):

Leaves fall off the trees in autumn, but many evergreens keep their needles year-round.

Comma + “but” (a FANBOYS) connects two independent clauses.

Example 3 (Colon):

One factor makes flamingos pink: their diet, which is rich in carotenoids.

Colon follows a complete clause and introduces an explanation.

Example 4 (Dashes):

Her answer—completely unexpected—surprised the committee.

Both dashes enclose a removable supplement.

Example 5 (Apostrophe):

Even the children’s laughter didn’t wake the tired dog.

Apostrophe for plural possessive; never use an apostrophe for plurals alone.

Quick Reference Table: SAT Punctuation

Mark	Usage	Example
Period (.)	End sentence; link two indep. clauses	The birds returned. They built a nest.
Semicolon (;)	Link indep. clauses (no FANBOYS)	It rained; we stayed in.
Colon (:)	After complete clause, introduce list/explanation	I need just one thing: courage.
Comma (,)	Lists, after intro, with FANBOYS, set off supplements	Tall, green trees lined the path.
Dash (—)	Set off/insert supplements or for emphasis	We all agreed—the concert was fantastic.
Apostrophe (’)	Contractions/possession (never for plurals)	Maria’s chair / they’re going

Test-Day Strategies

1. Know what each mark does.
Don’t substitute marks based on “feel.” Base your decision on sentence structure.

2. If you see options with all different marks, check if you’re linking two sentences, adding a list, or setting off a supplement.

3. Eliminate comma splices and semicolon misuse first.
These are the SAT’s most common traps.

4. Use the “cross-it-out” trick for supplements. The sentence should work without the insert.

Key Takeaways

Punctuation marks set boundaries in sentences. The right choice depends on grammar, not speech rhythm.
Only semicolons, periods, or comma+FANBOYS link full sentences—never use just a comma.
Colons must follow a complete sentence.
Supplements require matching punctuation. No lone commas or dashes.
If unsure, return to basics: split into simple sentences and look for grammar breaks.

Strong punctuation skills will let you ace the SAT and write with clarity in any setting!