A comma splice happens when two complete sentences — each one grammatically able to stand alone — get joined with nothing but a comma. A comma isn't strong enough to do that job on its own, which is why splices read as rushed or run-on even when every individual word is spelled correctly.
Check whether the text on either side of the comma could stand alone as its own sentence. If both halves make complete sense by themselves — "I finished the report." and "I sent it to my manager." — a lone comma between them is a splice.
Short, punchy, parallel clauses in informal or literary writing sometimes use splices deliberately for rhythm — "I came, I saw, I conquered" is technically a comma splice, and nobody minds. The rule matters most in formal, academic, and professional writing, where a splice reads as a mistake rather than a stylistic choice.
Comma splices often happen when you're writing quickly and the two ideas feel connected in your head, so the pause of a comma feels sufficient even though grammatically it isn't. An AI proofreading tool catches this reliably because it isn't relying on how the sentence "feels" — it's checking sentence structure directly.
Check your writing for comma splices →