An independent clause can stand alone as a sentence. A dependent clause cannot. Both have a subject and a verb. The difference is a word like because, although, or when at the front of the dependent clause, which leaves the reader waiting for more. On the SAT, telling the two apart decides the punctuation: a dependent clause that comes first takes a comma, and it can never stand alone after a period or a semicolon.
This page follows the rules in our lesson on joining an incomplete clause to a complete sentence. You can practice them in our Digital SAT question banks, sorted by test date.
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Video: Four Jobs and Job Two. From the Mr. O series Joining an Incomplete Clause to a Complete Sentence.
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What College Board tests
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Start 1-day free trial →Clause questions belong to the Boundaries skill in the Standard English Conventions domain. College Board's framework says that for Boundaries, "students must edit text to ensure that sentences are conventionally complete." Under its Within Sentences testing point, students "coordinate clauses within a sentence or elements in a series using appropriate punctuation and, in some cases, a conjunction or conjunctive adverb" and "recognize circumstances in which no punctuation is needed to set off sentence elements" (Assessment Framework for the Digital SAT Suite). That last part matters: some of the right answers on this skill have no punctuation at all.
Sentence or not? Three groups of words
| Words | Stands alone? | What is missing |
|---|---|---|
| The bridge was repaired in May. | Yes | Nothing. It has a subject, a working verb, and a finished thought. |
| Because the bridge was repaired in May | No | "Because" leaves you waiting. Because it was repaired, then what? |
| The bridge repaired in May | No | No working verb. "Repaired" only describes the bridge, so nothing happens in the sentence. |
The second line shows a word added to the front. The third line shows a verb taken away. Both breaks show up on the test, and they need different fixes. This page covers the first kind. Our guide to SAT sentence fragments covers the second.
The words that make a clause dependent
A subordinating word turns a full sentence into a clause that has to lean on another one. The clause keeps its subject and verb. It cannot finish on its own any more.
Common subordinating words: because, although, though, while, when, since, if, unless, after, before, whereas, until.
Relative words that start describing clauses: who, which, that, whose, where.
Our lesson notes sort every clause into one of four jobs. Name the job and the punctuation follows.
| Job | Signal words | Punctuation |
|---|---|---|
| 1. Stands alone (independent) | none | A period, a semicolon, or a comma plus for, and, nor, but, or, yet, so to join another one |
| 2. Attaches to the whole sentence | because, although, when, since, while, if, unless, whereas, though | Comma if it comes first. Usually none if it trails. |
| 3. Is the subject or object | that, what, which, whatever, whoever, how, why | None. It cannot be cut off or bracketed. |
| 4. Describes a noun | that, which, who | Commas only if you could delete the description and still know which one is meant |
Job 2: order decides the comma
| Order | Punctuation | Example |
|---|---|---|
| Dependent clause first | Comma where it ends | When the bell rang, the students packed their bags. |
| Dependent clause second | Usually no comma | The students packed their bags when the bell rang. |
The two ideas and the connecting word stay the same. Only the order changes the comma.
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Try it: a dependent clause that comes first
Although the jar was labeled as sample ______ pottery shard inside it came from a different dig site.
- B-17. The
- B-17, and the
- B-17, the
- B-17 the
Answer: C. "Although" starts a Job 2 clause, and that clause comes first, so a comma marks where it ends. Choice A puts a period after "Although the jar was labeled as sample B-17," which leaves that clause standing alone as a fragment. Choice B adds "and," which joins two clauses that can each stand alone, and the first one here cannot. Choice D gives no boundary at all.
Try it: a dependent clause that trails
A beekeeper can tell when a hive is about to swarm by watching the ______ the scouts leave in large numbers a day or two before the colony moves.
- entrance. Because
- entrance; because
- entrance because
- entrance, and because
Answer: C. The full sentence comes first, and the "because" clause trails behind it, so no mark is needed. Choices A and B put a strong mark in front of the "because" clause, which then has to stand alone, and it cannot. Choice D adds "and," but there is no second independent clause for it to join.
Video: Order Decides the Comma. From the Mr. O series Joining an Incomplete Clause to a Complete Sentence.
Drill: independent or dependent?
Decide whether each line could stand alone. Then check the answer column.
| # | Words | Answer |
|---|---|---|
| 1 | The bus left at noon. | Independent. It stands alone. |
| 2 | When the bus left at noon | Dependent. "When" leaves it waiting. |
| 3 | Because the storm knocked out the power | Dependent. It needs a main clause, such as "we used candles." |
| 4 | The storm knocked out the power. | Independent. |
| 5 | Although Mia studied all week | Dependent. |
| 6 | Mia studied all week, so she felt ready. | Two independent clauses joined by a comma and "so." |
| 7 | Which surprised everyone. | Dependent. A statement that starts with "which" is a fragment. |
| 8 | The coach who trained us retired. | Independent. It contains the clause "who trained us," which tells you which coach. |
Job 3: when the clause is the subject
Words like that, what, and which can start a clause that fills the subject slot. Then the clause is not hanging off the sentence. It is the sentence's subject, and you never put a mark between a subject and its verb. The test from our notes: read to the end of the clause, then look at the next word. If it is a verb with no subject in front of it, the clause is the subject.
That the old barn was built without a single ______ the engineers who inspected it.
- nail, surprised
- nail surprised
- nail; surprised
- nail. Surprised
Answer: B. The whole clause "That the old barn was built without a single nail" is the subject of "surprised." Choice A puts a comma between the subject and its verb. Choices C and D leave "surprised the engineers" with no subject.
Compare the two openers. "Although the barn was built without nails, it still stands" needs a comma. "That the barn was built without nails surprised everyone" takes none. Different job, different rule.
Job 4: when the clause describes a noun
One question decides the comma: could you delete the clause and still know which one the sentence means? If deleting it loses which one, the clause is essential and takes no comma, even when it starts with "who." If the meaning survives, the clause is extra and takes a comma on each side.
The museum hires many guides each summer, but it gives the tower keys only to the guide ______ finished the fire safety course.
- , who has
- who has
- . Who has
- ; who has
Answer: B. Without the clause, you would not know which guide gets the keys. The clause is essential, so it takes no comma. Choices C and D cut "who" loose from "guide," which leaves a fragment.
How the clause type decides the punctuation
| What sits on each side | What works | What fails |
|---|---|---|
| Independent + independent | Period, semicolon, or comma plus and, but, so (and the other FANBOYS words) | A comma alone (comma splice) |
| Dependent first + independent | Comma | Period or semicolon after the dependent clause |
| Independent + dependent second | Usually no mark | Period or semicolon before the dependent clause |
| Clause as subject + its verb | No mark | Any mark between them |
| Extra describing clause in the middle | A comma on each side | One comma with no partner |
For the first row in depth, read our period rule for independent clauses and punctuating clauses on the Digital SAT. For phrases that open a sentence, see the SAT comma rule for introductory phrases, and for every rule on one page, the SAT grammar rules cheat sheet.
Practice next
The Sentence Boundaries lesson notes cover fragments and extra information, and they need a free account. The June 2026 English question bank is free to open. When you want a timed check, create a free account and take one full-length adaptive practice test free.
Frequently Asked Questions
What is the difference between an independent and a dependent clause?
Both have a subject and a verb. An independent clause finishes its thought and can stand alone. A dependent clause starts with a word like because, although or when, so it must attach to an independent clause.
Which words make a clause dependent?
Subordinating words such as because, although, though, while, when, since, if, unless, after, before, whereas and until. Relative words such as who, which and that also start clauses that cannot stand alone as statements.
Do you put a comma after a dependent clause?
Yes, when the dependent clause comes first: When the bell rang, the students packed their bags. When it comes second, it usually takes no comma: The students packed their bags when the bell rang.
Can a dependent clause follow a period or a semicolon?
Not by itself. A period or semicolon needs a complete sentence after it. A dependent clause on its own after one of those marks is a fragment.
Can a whole clause be the subject of a sentence?
Yes. In That the barn was built without nails surprised everyone, the that clause is the subject of surprised, so no comma goes between them.