Comma Splices

A comma splice happens when two complete sentences get joined by nothing but a comma. 'The kiln cooled overnight, the glaze cracked anyway' sounds fine because both halves read smoothly and the idea connects, but grammar doesn't care about smoothness. It cares about structure. Each half has its own subject and verb and could stand alone as a sentence, which means a comma alone can't hold them together. You need a period, a semicolon, or a comma plus a word like 'and' or 'but'.

The test for a splice is mechanical, not musical. Cover one side of the comma at a time and ask: does this have a subject and a verb, and could it end with a period? If both sides pass, the comma is doing too little work. This catches splices even when a word like 'then' sits right after the comma, since 'then' is not a conjunction and does nothing to the boundary. It also catches splices hidden by length, like a short four-word clause, or disguised by a long modifier sitting between the subject and verb, like a phrase about distance or temperature.

This topic sits next to run-ons and fragments because all three are about where one sentence legally stops. A run-on is the same error with no punctuation at all; a fragment is the opposite problem, a piece that can't stand alone being punctuated as if it could. Once you can test a clause for independence, you can diagnose all three boundary errors with the same move.