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Common mistake Punctuation and style

Joining two sentences (no comma splice)

Comma splice: what it is and how to fix it

Two full sentences joined only by a comma, or run together with no punctuation (for example "Prices rose, people bought less."). In short: A comma cannot join two full sentences.

This guide is for writers moving from B1 to B2 or from B2 to C1.

The rule for comma splice

A comma cannot join two full sentences. Use a full stop, a semicolon, or a joining word such as and, but, so or because. Put a full stop or a semicolon before “however” and “therefore”.

Pattern: Use a full stop, a semicolon, or a joining word: and, but, so, because, although. "However" and "therefore" need a full stop or a semicolon before them.

Used correctly: two full sentences correctly joined with a full stop, a semicolon, or a linking word (for example "Prices rose; as a result, people bought less.").

Use this when you put two full sentences, each with its own subject and verb, side by side. A comma alone cannot join them.

Comma splice: wrong and right examples

  • Wrong My phone died, I could not call you.

    Right My phone died, so I could not call you.

  • Use a semicolon

    Wrong The museum is free, however, few people visit it.

    Right The museum is free; however, few people visit it.

More right sentences

  • Prices rose. People bought less.
  • Prices rose; as a result, people bought less.
  • Prices rose, so people bought less.

Traps to avoid with comma splice

  • Not "The plan is cheap, however it is slow." Write "The plan is cheap; however, it is slow."
  • "It" and "this" often start a new sentence: "I like the city. It is lively."

Skills that train comma splice

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