Notes from the Proofreader: The Comma Splice

Welcome to “Notes from the Proofreader”: a semimonthly discussion of grammar, usage, and punctuation pitfalls. In this post, we’ll be discussing the pesky comma splice (aka the run-on sentence).

The comma is a useful little piece of punctuation. Among it’s many jobs, it can separate coordinate adjectives and items in a series. It can also set off elements: introductory phrases, parenthetical information, nonrestrictive clauses and phrases, names used in direct address, etc. The 16th edition of The Chicago Manual of Style 6.16–6.53 offers a more comprehensive list of its uses.

What a comma cannot do is hold together independent clauses all by itself.* It’s just not strong enough. The comma requires the help of a conjunction to successfully join them. Or it can be replaced by a stronger piece of punctuation. Or the offending splice can be revised so that there’s only one independent clause.


  • Take for example this comma splice: “Fill out this short survey, we’ll send you a $100 credit.” Each clause in this splice is an independent clause and can function as a complete sentence on its own. The poor little comma is not up to the task of holding the clauses together. Here are some easy ways to fix this splice.
  • Fill out this short survey, and we’ll send you a $100 credit. (Add a coordinating conjunction.)
  • Fill out this short survey; we’ll send you a $100 credit. (Replace comma with the stronger semicolon. Typically avoided in marketing copy.)
  • Fill out this short survey—we’ll send you a $100 credit. (Replace comma with an em dash. CMoS is silent on this usage, but it occurs often in marketing copy.)
  • Fill out this short survey. We’ll send you a $100 credit. (Replace comma with a period and separate into two sentences.)
  • If you fill out this short survey, we’ll send you a $100 credit. (Revise so only one clause is independent. See CMoS 6.30 and 6.31)


Let’s make sure we don’t give the comma more than it can handle.

*Except in “those rare case when one has a trio of short independent clauses that all have the same grammatical subject: He came, he saw, he conquered.” (Amy Einsohn. The Copyeditor’s Handbook, 2nd Ed. [University of California Press, 2006], 80)