The Essentials of Writing

The Hamilton College Style Sheet

Essentials of English Usage

Comma Splice ("cs")

Separate independent clauses with a comma only when they are joined by a coordinating conjunction.

This is not as complicated as it sounds.  A comma splice occurs when you use a comma without and, but, for, nor, or, so, or yet (these are the coordinating conjunctions) when joining two clauses.  Grammar-checkers won't always catch comma splices; however, you can correct a comma splice by dividing the two clauses into separate sentences, by replacing the comma with a semicolon, by subordinating one of the clauses, or by adding a coordinating conjunction.

 1. It snowed all night, none of the paths were plowed this morning.
[Comma splice. Try two sentences: It snowed all night. None of the paths were plowed this morning.]

 2. The students looked sleepier than usual, they had sat up most of the night studying for the exam.
[Comma splice. Try a coordinating conjunction: The students looked sleepier than usual, for they had....]

 3. I have been proofreading this paper all day, I can no longer see my errors.
[Apparently. Comma splice. Try subordinating the first clause:  Because I have been proofreading this paper all day, I can no longer....]

 4. She had eaten nothing but lettuce all week, however she still couldn't fit into her black pants.
[Comma splice. Try a semicolon: She had eaten nothing but lettuce all week; however, she still.... Note that however is a conjunctive adverb, not a coordinating conjunction. See Semicolon ("semi") for other conjunctive adverbs.]

See also Punctuation ("p"), Semicolon ("semi"), and Subordination ("su"), in this handbook. Refer also to Punctuation Patterns.