How to Fix Run-On Sentences and Comma Splices

A sentence can be long without being a run-on, and short without being correct. What matters is how two complete thoughts are joined. Once you can recognise a complete thought, called an independent clause, run-ons and comma splices become easy to find and even easier to fix.

What counts as a complete thought?

An independent clause contains a subject and a verb and makes sense on its own:

• The game ended.
• She played the Q on a triple-letter square.

A dependent clause also has a subject and a verb, but it starts with a word like because, when, although or if, which makes it lean on another clause:

• because the game ended (incomplete on its own)

Run-ons and comma splices only happen when two independent clauses are joined incorrectly.

The two errors

Run-on (fused sentence):

The bag was empty the game was over.

Two complete thoughts collide with nothing between them.

Comma splice:

The bag was empty, the game was over.

A comma is too weak to hold two independent clauses together on its own. Comma splices are far more common than fused sentences, because the comma feels like a natural pause.

Five ways to fix them

Take the splice The bag was empty, the game was over. Each fix below is correct; the best one depends on the relationship between the ideas.

1. Use a full stop

The bag was empty. The game was over.

The simplest fix. It works well when the ideas are related but you want each to land separately.

2. Use a semicolon

The bag was empty; the game was over.

A semicolon joins two closely related independent clauses. It signals that the second idea follows directly from the first. See our lesson on semicolons and colons for more.

3. Add a comma and a coordinating conjunction

The bag was empty, so the game was over.

The seven coordinating conjunctions are for, and, nor, but, or, yet, so, often remembered as FANBOYS. A comma plus one of these can join two independent clauses.

4. Make one clause dependent

Because the bag was empty, the game was over. The game was over because the bag was empty.

Adding a subordinating word such as because, since, when, although or after turns one clause into a supporting idea. This often makes the relationship clearest.

5. Rewrite the sentence

With the bag empty, the game was over.

Sometimes the neatest solution is to restructure the sentence so that only one independent clause remains.

The "however" trap

Words like however, therefore, moreover, otherwise and meanwhile are conjunctive adverbs, not conjunctions. They cannot join two independent clauses with just a comma:

• ✗ I wanted to play, however, the board was full.
• ✓ I wanted to play; however, the board was full.
• ✓ I wanted to play. However, the board was full.

If you can move the word to another spot in the clause (the board, however, was full), it is an adverb and needs a semicolon or full stop before it.

How to find run-ons in your own writing

1. Read aloud. Where your voice drops and you take a breath, check whether a new independent clause starts.
2. Look at every comma. Ask: could the words on both sides stand alone as sentences? If yes, and there is no FANBOYS word after the comma, you have a splice.
3. Watch the pronouns. Splices often hide before it, he, she, they and this: The rule is simple, it applies to everyone.
4. Check transitions. Every however or therefore in the middle of a sentence deserves a second look.

Long is not the same as wrong

A long sentence can be perfectly correct if its clauses are joined properly:

When the last tile was drawn, the players counted their scores, and although the margin was only three points, everyone agreed it had been the best game of the night.

This sentence has several clauses, but each one is connected with a subordinating word or a comma plus a conjunction. Length alone never makes a run-on.

Practice quiz