The one rule that unlocks the whole section
Almost every SAT punctuation question reduces to a single yes-or-no question: is each side of the punctuation a complete sentence?
If you can answer that, you can answer the question, even when you don't remember the textbook rule. So that's where we'll start.
A complete sentence (also called an independent clause) has a subject and a verb and could stand alone. "The chef arrived." Complete. "After the chef arrived": not complete; it's leaning on something.
The four-square decision tree
| Left side | Right side | What works |
|---|---|---|
| Complete | Complete | Period · Semicolon · Comma + FANBOYS conjunction · Colon (if right side explains) |
| Complete | Fragment | Colon · Dash · Comma (sometimes) |
| Fragment | Complete | Comma (after intro phrase) |
| Fragment | Fragment | Usually nothing at all |
The big four punctuation marks, in plain English
Period and semicolon: the "full stop" twins
A semicolon is a period in a fancy outfit. If you can replace the semicolon with a period and have two grammatical sentences, the semicolon works. If not, it doesn't. That's the whole rule.
Wrong: "Although it rained; we played outside." ("Although it rained" isn't a complete sentence.)
Right: "It rained; we played outside anyway."
Comma: the most overused mark
Commas are the SAT's favorite trap because students sprinkle them like seasoning. The SAT only accepts commas in five situations:
- Between items in a list of three or more.
- After an introductory phrase.
- Around a non-essential clause (bookends).
- Before a FANBOYS conjunction (for, and, nor, but, or, yet, so) joining two complete sentences.
- To separate certain coordinate adjectives ("a tall, wooden door").
If you can't name which of those five rules applies, the comma is probably wrong. When in doubt, take the comma out and read the sentence again.
Colon: the "watch this" mark
A colon needs a complete sentence on its left. Whatever follows can be a list, a phrase, or another sentence; it just has to explain or specify what came before.
Right: "He wanted one thing: silence."
Right: "The verdict was unanimous: the bridge had to be rebuilt."
Wrong: "He wanted: silence." (Left side isn't complete.)
Dash: the dramatic mark
For SAT purposes, a dash is interchangeable with a colon when introducing a phrase, and interchangeable with a comma when bookending a non-essential clause, with one important rule: matched bookends. If a non-essential clause opens with a dash, it must close with a dash. You can't open with a dash and close with a comma.
Non-essential vs. essential: the bookends rule
Information that could be removed without breaking the sentence's core meaning gets bookended in commas (or dashes, or parentheses). Information the sentence needs doesn't get bookended at all.
Removable: "My sister, who lives in Atlanta, is visiting." (You only have one sister.)
Necessary: "The student who scored highest will give the speech." (Which student? The clause tells us.)
The SAT trap is opening with one mark and closing with another, like a comma and a dash. Matched bookends always.
The list-with-internal-commas trick
When list items already contain commas, the SAT uses semicolons to separate them:
"The committee includes Maria Rodriguez, the chair; Devin Park, the treasurer; and Aisha Smith, the secretary."
Worked example
"Marie Curie discovered two new elements_____ polonium and radium."
Left side: complete sentence. Right side: a phrase (a list, not a sentence). What punctuation introduces an explanation or list after a complete sentence? A colon, or a dash. A comma is acceptable here too, because "polonium and radium" functions as an appositive renaming "two new elements." So the SAT will usually offer either a colon or a comma; what they will not offer is a semicolon, because the right side isn't a complete sentence.
Practice this skill efficiently
- For every punctuation question you miss, write the rule in your own words. By question 30, you'll have a personal cheat sheet of the rules you tend to forget.
- Read sentences aloud (in your head) and feel the natural pauses. The SAT's punctuation usually matches a careful reader's natural rhythm.
- When all four answers feel possible, ask which side of the punctuation is complete. The grid above almost always picks the winner.