A comma splice happens when a writer joins two complete sentences with just a comma. Purdue OWL defines comma splices as compound sentences that are not punctuated correctly, and Merriam-Webster defines a comma splice as the error of using a comma between coordinate main clauses not connected by a conjunction.

❌ I finished the report, I sent it to the client.

This is a comma splice because both clauses are independent. Purdue explains that one common fix is to separate them into two sentences.

✅ I finished the report. I sent it to the client.

✅ I finished the report; I sent it to the client.

✅ I finished the report, and I sent it to the client.

Purdue OWL lists these as standard ways to repair a comma splice.

❌ The deadline was tight, we still finished on time.

✅ The deadline was tight, but we still finished on time.
✅ The deadline was tight; we still finished on time.

The most common mistake is thinking that a comma is strong enough to join any two related ideas.

It isn’t.

A comma works well for:

But when you have two full independent clauses, you usually need:

Another common mistake is confusing a comma splice with any long sentence. The real issue is not sentence length. The issue is whether two complete thoughts are being joined with only a comma.

Use this fast test:

Ask yourself:

If the answer is yes to both, then a comma by itself is probably not enough. Purdue’s guidance says you can usually fix the problem by using a period, a semicolon, or a comma with a coordinating conjunction.

A simple memory trick:

Two full sentences? One comma is not enough.