SAT® punctuation rules: commas, semicolons, colons and dashes
Most punctuation questions on the digital SAT come down to one decision: is each side of the punctuation mark a complete sentence or not? Learn to spot independent clauses, and the rules below cover nearly every question.
The short version
- Two complete sentences can be joined by a period, a semicolon, or a comma plus and, but, or, nor, for, so, yet. Never by a comma alone.
- A colon or a dash needs a complete sentence before it. After it can come a list, an explanation or another sentence.
- Extra information in the middle of a sentence takes matching marks on both sides: two commas, two dashes or two parentheses.
- No single comma between a subject and its verb, or a verb and its object.
First, find the independent clauses
An independent clause has a subject and a verb and can stand alone as a sentence: the river flooded. A dependent clause starts with a word like because, although, when, which or that and can’t stand alone: because the river flooded. Before you pick an answer, cover the punctuation mark and ask whether the words on each side could be their own sentence.
Rule 1: joining two complete sentences
| Works | Doesn’t work |
|---|---|
| The museum opened at nine. The line was already long. | The museum opened at nine, the line was already long. (comma splice) |
| The museum opened at nine; the line was already long. | The museum opened at nine the line was already long. (run-on) |
| The museum opened at nine, but the line was already long. | The museum opened at nine; but the line was already long. |
| The museum opened at nine; however, the line was already long. | The museum opened at nine, however, the line was already long. |
The last row is the one students miss most. Words like however, therefore, moreover and for example are not joining words. Between two complete sentences they need a semicolon or a period before them and a comma after.
Rule 2: colons and single dashes
A colon (or a single dash, which does the same job) says “here is what I mean.” The part before it must be a complete sentence.
Wrong: The recipe needs: flour, butter and two eggs.
Right: The recipe needs three things: flour, butter and two eggs.
The words before the colon must stand alone. "The recipe needs" doesn’t, so the colon is wrong there.
Rule 3: extra information takes a matching pair
A phrase you could lift out without breaking the sentence is set off on both sides, with the same mark each time.
Wrong: Dr. Okafor, the lead engineer on the bridge — signed the final plans.
Right: Dr. Okafor, the lead engineer on the bridge, signed the final plans.
A comma opens the extra phrase, so a comma must close it. Mixing a comma with a dash is never right.
Test it: remove the phrase between the marks. Dr. Okafor signed the final plans still works, so both commas belong.
Rule 4: no comma between a subject and its verb
Wrong: The students who finished the survey early, received a second page.
Right: The students who finished the survey early received a second page.
The subject is "the students who finished the survey early" and the verb is "received". One comma between them is wrong, however long the subject.
The same goes for a verb and its object, and for a word like that right before its clause.
Rule 5: restrictive or not
If a clause tells you which one, it is essential and takes no commas. If it only adds detail about something already identified, set it off with commas.
- The volunteers who arrived first got the best jobs. (Which volunteers? The ones who arrived first: no commas.)
- Maya, who arrived first, got the best job. (We already know who Maya is: commas.)
Apostrophes, briefly
- One owner: the student’s notes. Several owners ending in s: the students’ notes.
- Its shows ownership; it’s means it is. Same pattern for their and they’re.
- Plurals never take an apostrophe: three sections, not three section’s.
A fast method for any punctuation question
- Find the subject and verb on each side of the blank.
- Decide: complete sentence + complete sentence, complete sentence + list or explanation, or one sentence with extra information.
- Cross out every choice that breaks the matching rule above, then read the survivor in full.
Practice this on Peakscor’s Boundaries lessons, then drill Boundaries at any difficulty. Every question comes with an explanation of the rule it tests. Not sure which skills to work on first? The free 20-question diagnostic shows your level in every domain.
All examples on this page were written by Peakscor. Peakscor is an independent practice tool and is not affiliated with College Board.
Questions
What punctuation is tested on the SAT?
Commas, semicolons, colons, dashes, periods and apostrophes, mostly where one part of a sentence ends and the next begins. These questions are part of Standard English Conventions in the Reading and Writing section.
What is a comma splice?
Two complete sentences joined by only a comma, as in "The bus was late, we walked." Fix it with a period, a semicolon, or a comma plus a word like and, but or so.
When do you use a semicolon instead of a comma?
Use a semicolon between two complete sentences that are closely related and not joined by and, but, or, so or yet. A comma alone can’t do that job.
Can a colon follow an incomplete sentence?
No. On the SAT, the words before a colon must be a complete sentence. What comes after it can be a list, a phrase or another sentence.
Is it OK to put a comma between a subject and its verb?
No. A single comma should never separate a subject from its verb or a verb from its object, however long the subject is.
Practice Boundaries
Learn the rules with worked examples, then drill them at any difficulty. The first lesson of every module is free.
Open the Boundaries lesson