A comma splice happens when two complete sentences, each with its own subject and verb, are joined by a comma alone:
- The meeting ran long, we missed the train.
- I love this café, the coffee is excellent.
Each half could stand on its own as a sentence. Grammarians call such a half an independent clause. A comma is not strong enough to hold two of them together, so the sentence reads as if it trips over itself. A comma splice is one kind of run-on sentence.
Four ways to fix a comma splice
- Make two sentences. The meeting ran long. We missed the train. The plainest fix, and often the best one.
- Use a semicolon. The meeting ran long; we missed the train. A semicolon says the two thoughts are closely linked.
- Add a joining word after the comma. The meeting ran long, so we missed the train. The seven coordinating conjunctions are for, and, nor, but, or, yet and so, easy to remember as FANBOYS.
- Make one clause depend on the other. Because the meeting ran long, we missed the train. Words like because, although, when and since turn a clause into one that can no longer stand alone.
Which one to choose depends on the relationship you want to show. A full stop keeps the two ideas separate, a semicolon pairs them, and a conjunction or a subordinate clause spells out how they are connected: cause, contrast, time.
The however trap
Words such as however, therefore, moreover and otherwise feel like joining words, but they are not conjunctions. They are adverbs, and a comma in front of them still leaves a splice:
- Splice: The forecast was bad, however we went sailing.
- Fixed: The forecast was bad; however, we went sailing.
- Also fixed: The forecast was bad. However, we went sailing.
If you can move the word to another place in the clause (we went sailing, however), it is an adverb and needs a semicolon or a full stop before it.
When writers break the rule on purpose
Very short, parallel clauses are sometimes joined with commas for rhythm, and most readers accept it: I came, I saw, I conquered. Novelists use splices in dialogue and in fast-moving passages, too. In emails, reports, essays and anything formal, the reader will take a splice as a mistake, so it is safest to fix it.
How to find them in your own writing
Look at each comma in a long sentence and ask whether the words on both sides could be full sentences on their own. If they could, and nothing but the comma sits between them, you have found a splice. Reading the text aloud helps: where you naturally pause and drop your voice, as at the end of a sentence, a comma is usually not enough.
How the spell checker helps
Comma splices are hard for any automatic check, because it has to work out where one clause ends and the next begins, and a sentence can be correct with the very same comma in it. The Spell Checker covers the spelling, grammar and punctuation around them; for sentence structure like this, the AI Spell Checker, which reads text in context, is the one to try, followed by your own read-through.