You’ve run your draft through every grammar checker, cleaned up the red underlines, and polished until there are no errors left. At least, according to the five AI checkers you just ran it through and your large language model.
So why does your writing still feel… off?
Here’s the truth: AI tools don’t always catch the most subtle mistakes. And one of the biggest culprits is a grammar slip-up that even seasoned writers miss.
Readers won’t flag it. They won’t leave a comment about it. But they will notice something’s wrong. Your sentences will feel rushed, unpolished, or amateurish, even if everything else is technically correct.
The mistake? The comma splice.
What Is a Comma Splice?
A comma splice happens when two complete sentences (independent clauses) are joined with just a comma and nothing else holding them together.
Example:
The sun was setting, we hurried home.
Both halves—“The sun was setting” and “We hurried home”—could stand alone as full sentences. This means that the comma, on its own, isn’t strong enough to glue them together.
And while AI grammar tools sometimes do catch this mistake, many don’t. To further complicate things, the sentence “sounds right” when read aloud, which tricks the algorithm and the writer, so reading it aloud may not even catch this mistake.
Why Readers Notice (Even If They Don’t Know Why)
Your audience doesn’t need to know the technical definition of a comma splice to feel its effect.
Sentences with splices read like run-ons: rushed, uneven, and sloppy. The rhythm is wrong. The professionalism slips.
And repeated comma splices make your prose feel jagged, pulling readers out of the story or message.
AI may shrug and say it’s fine. But your readers won’t.
Common Examples That Slide Past AI
Here are a few splice-heavy sentences that often escape detection:
- She loves thrillers, she reads one every week.
- I wanted to go to the party, I had already made plans.
- He’s a great writer, his grammar needs work.
- The rain poured down, we kept walking anyway.
At a glance, they look harmless. In casual conversation, they sound fine. But in writing, they chip away at flow and clarity.
How to Fix a Comma Splice (3 Easy Ways)
The good news? Splices are simple to fix. Here are three methods:
- Add a coordinating conjunction (FANBOYS):
The sun was setting, and we hurried home. - Break it into two sentences:
The sun was setting. We hurried home. - Use a semicolon for closely related ideas:
The sun was setting; we hurried home.
Each fix works—the best one depends on your rhythm and tone.
Why AI Won’t Save You From This Mistake
AI writing tools can polish your prose, fix typos, and even suggest smoother phrasing. But here’s the catch: many algorithms lean too heavily on what sounds conversational. If it flows, they’ll let it pass—even when the sentence is technically wrong.
That’s why grammar slips like comma splices so often slip under the radar. The AI “thinks” it’s fine, but your readers feel the difference. They may not know the rule, but they’ll sense that something in your writing is off—rushed, unpolished, or just a little awkward.
And readers always notice what algorithms don’t.
Bonus: When It’s Okay to Break the Rule
Yes, comma splices are usually mistakes. But skilled writers sometimes use them deliberately for effect—especially in dialogue or fast-paced narration.
- Dialogue:
“I don’t know, I just… I can’t.” - Narrative urgency:
The clock struck midnight, the city fell silent.
The difference? Intentionality.
You know the rule, you choose to break it. That’s not a mistake—that’s style.
The Real Fix
The solution isn’t to stop using AI—it’s to stop relying only on it. Use tools to catch the easy stuff, but trust your own editorial eye for the subtle fixes. Once you train yourself to spot errors like comma splices, you’ll have an advantage no algorithm can give you: writing that feels smooth, intentional, and professional.
Your readers will thank you—even if they can’t explain why your sentences just work.