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What are run-on sentences?

This section introduces run-on sentences and shows how connecting words and phrases are used to join simple sentences to create complex ones.

The rule

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Run-on sentences are sometimes called ‘fused sentences’ or ‘comma splices’.

They usually happen when you join two simple sentences with:

  • a comma by itself


  • a comma with a conjunction that cannot be used to join sentences.

You can join two simple sentences with either:

  • a co-ordinating conjunction e.g. so, or, and, but


  • a subordinating conjunction e.g. because, although, if.

If you don’t use either a co-ordinating or subordinating conjunction, each sentence remains a sentence in its own right. You must use a full stop to show this.

Sentence run-on has nothing to do with the length of a sentence. Sentence run-on is a grammatical error. Sentences can be long and complex, and still be grammatically correct.