What a comma splice is, how to spot one, and four ways to fix it
A comma splice joins two complete sentences with only a comma: "I finished the draft, it was too long." It is a classic thing for a copy editor to flag. Here is how to spot one, the "however" trap, four ways to fix it, and the rare times a comma splice is the right call.
How to spot one
Chicago's blog, CMOS Shop Talk, describes the rule most writers learn: do not join, or splice, two independent clauses with a comma alone. An independent clause is anything that could stand on its own as a sentence.
The test: cover the comma with your finger. If what is on each side could be its own sentence, and there is no joining word like "and," "but" or "so" after the comma, you have a comma splice.
- Splice: My editor sent notes, most of them were about chapter 3.
- Not a splice: My editor sent notes, and most of them were about chapter 3.
- Not a splice: My editor sent notes about chapter 3. (One clause, no comma needed.)
The however trap
Words like however, therefore, then and still look like joining words, but they are not. A comma before them still leaves a splice:
- Splice: The first draft was strong, however, the ending needed work.
- Fixed: The first draft was strong; however, the ending needed work.
- Also fixed: The first draft was strong. However, the ending needed work.
Search your manuscript for ", however," and ", then " to find these quickly.
Four ways to fix it
The Chicago blog lists the standard fixes (a period, a semicolon, or a coordinating conjunction) and notes that each one changes the emphasis, so context and tone decide which to use. A fourth option is to make one half depend on the other.
| Fix | Example | Effect |
|---|---|---|
| Period | I finished the draft. It was too long. | Two firm, separate points |
| Semicolon | I finished the draft; it was too long. | Keeps two closely linked ideas together |
| Comma plus and, but, so, or, yet, for, nor | I finished the draft, but it was too long. | Shows how the ideas relate |
| Make one part depend on the other | When I finished the draft, it was too long. | Puts the weight on one idea |
Examples written by Scribe Media.
Comma splice vs run-on
The Chicago blog notes that some grammarians separate a run-on, or fused sentence, which has no punctuation at all between the two clauses ("I finished the draft it was too long"), from a comma splice, which has just a comma. In practice, it says, comma splices are often grouped with fused sentences as run-ons. The fixes are the same.
When a comma splice is fine
The same post says a comma splice is sometimes the best choice, and that it can work when the clauses are short and repetitive, especially in an informal tone, as in its own example: "A comma splice isn't an error, it's an option." In dialogue, people speak in splices, and you can let them stand.
In the narration of a nonfiction book, though, most copy editors will fix them. If you use one on purpose, tell your editor so it is not "corrected." See what a copy editor does, and for other choices your editor will ask about, that vs which and the Oxford comma.
Start here: read one chapter aloud and stop at every comma. If you could put a period there and both halves would still be sentences, check for a joining word. No joining word, no comma alone.
Common questions
What is a comma splice?
Two complete sentences joined with only a comma: "I finished the draft, it was too long." Each half could stand alone as a sentence, so a comma is not enough to hold them together. It is also called a comma fault.
How do you fix a comma splice?
Four ways: use a period ("I finished the draft. It was too long."), a semicolon ("I finished the draft; it was too long."), a comma plus a joining word such as and, but or so ("I finished the draft, but it was too long."), or make one half depend on the other ("When I finished the draft, it was too long.").
What is the difference between a comma splice and a run-on sentence?
Some grammarians use "run-on" or "fused sentence" only for two sentences jammed together with no punctuation at all, and "comma splice" for two joined with just a comma. In practice, comma splices are often grouped with fused sentences as run-ons.
Is a comma splice ever acceptable?
Sometimes, for effect. Chicago's blog notes a comma splice is sometimes the best choice, especially with short, parallel clauses in an informal tone: "It isn't a mistake, it's a choice." In most book narration, though, editors will fix them.
Sources: CMOS Shop Talk (The Chicago Manual of Style's blog), Russell Harper, Comma Splices and Run-On Sentences (definition; comma fault; fixes and their effect on emphasis; run-ons and fused sentences; when a comma splice is acceptable), read November 1, 2026. The test, examples and guidance were written by Scribe Media. Published by Scribe Media.