SAT writing: how to spot and fix comma splices and run-ons
A comma splice joins two complete sentences with only a comma. A run-on (also called a fused sentence) joins them with nothing at all. The SAT Writing questions on sentence boundaries ask you to notice these and choose a clean fix. The skill is small and learnable: it comes down to recognizing when each side of a break can stand alone.
The one-question test
At any comma or break, ask: could the words on each side be a complete sentence by themselves? A complete sentence, or independent clause, has a subject and a verb and does not start with a word like because, although or when. If both sides pass, a comma alone is not enough.
Example
“The library closes at nine, we should leave at eight-thirty.”
“The library closes at nine” stands alone. “We should leave at eight-thirty” stands alone. Two sentences are joined by a comma, so this is a comma splice.
Five clean fixes
| Fix | Result |
|---|---|
| Period | The library closes at nine. We should leave at eight-thirty. |
| Semicolon | The library closes at nine; we should leave at eight-thirty. |
| Comma and a conjunction (for, and, nor, but, or, yet, so) | The library closes at nine, so we should leave at eight-thirty. |
| Make one side dependent | Because the library closes at nine, we should leave at eight-thirty. |
| Colon, when the second part explains the first | We should leave at eight-thirty: the library closes at nine. |
A semicolon needs a complete sentence on both sides, and a colon needs one before it. A semicolon already does the joining that “and” would do, so “; and” is not standard.
The however trap
Words like however, therefore, moreover, instead and for example look like connectors, but they are not conjunctions, and a comma before them does not join sentences.
Splice
The experiment was repeated twice, however the results did not change.
Fixed
The experiment was repeated twice; however, the results did not change.
Put the semicolon (or a period) before the transition word and the comma after it.
Not every comma is an error
- A dependent opener followed by a comma is correct: “Although the results did not change, the team repeated the test.”
- A comma plus a conjunction between two complete sentences is correct: “The footbridge opened in 1932, and it carried rail traffic for decades.”
- One subject with two verbs usually needs no comma: “The footbridge opened in 1932 and carried rail traffic for decades.”
- A dependent clause alone is a fragment, not a splice: “Although the results did not change.”
Practice question
Which choice completes the text so that it conforms to the conventions of Standard English?
The museum’s new exhibit features maps from the 1600s ______ visitors can compare them with satellite images taken this year.
- 1600s, visitors can
- 1600s; and visitors can
- 1600s, and visitors can
- 1600s and, visitors can
Show the answer and why
C. Both sides of the break are complete sentences, and a comma plus and joins them correctly.
A is a comma splice. B puts “and” after a semicolon, which is not needed and not standard. D puts a comma inside the conjunction and still has no clean boundary.
Check yourself
Which of these is a comma splice? (a) The bridge opened in 1932, it carried rail traffic for decades. (b) The bridge opened in 1932, and it carried rail traffic for decades. (c) The bridge opened in 1932 and carried rail traffic for decades. (d) The bridge opened in 1932, however it carried little traffic at first.
Show answers
(a) and (d) are comma splices. (a) joins two sentences with a comma; (d) uses however, which cannot join them. (b) and (c) are correct.