Comma splice

A comma splice occurs when two independent clauses are joined with nothing but a comma. An independent clause is a group of words that could stand alone as a complete sentence, and a bare comma is not strong enough to connect two of them. "The test starts at nine, you should arrive early" is a comma splice: each half is a complete sentence.

There are several standard fixes. You can split the clauses into two sentences with a period. You can replace the comma with a semicolon if the ideas are closely related. You can keep the comma but add a coordinating conjunction — one of the FANBOYS (for, and, nor, but, or, yet, so): "The test starts at nine, so you should arrive early." Or you can subordinate one clause: "Because the test starts at nine, you should arrive early."

Watch out for conjunctive adverbs like however, therefore, and moreover. They feel like conjunctions but cannot glue clauses together with just a comma — "I studied hard, however I failed" is still a splice. Correct punctuation uses a semicolon before the adverb and a comma after it: "I studied hard; however, I failed."

Comma splices are a staple of the English and writing sections of the ACT, SAT, and CLT. These exams present a spliced sentence among the answer choices and ask you to select the properly punctuated version, so learn to spot two independent clauses quickly and know all the legal ways to join them.