Fragments, Run-Ons & Comma Splices

Three of the most-circled mistakes in the whole of writing are really the same skill wobbling in three different directions. Fragments, run-ons and comma splices are all about one thing: where one sentence ends and the next one begins. Once you can spot a complete sentence, all three fixes fall neatly into place — you're not learning three separate rules, you're learning one.

Why this happens to everyone

Here's the thing worth knowing: this isn't a sign you're bad at writing. It's usually a sign you're thinking faster than your sentences can join up. Your brain stacks whole ideas side by side and trusts the reader to keep up. When you're chatting or texting a friend, they can — they fill the gaps. But in an essay or a story, the reader only has the words on the page, and if the joins between your ideas aren't clear, they get lost. That's all these three errors are: joins that didn't quite work. Spot the join, and you can fix almost any of them in under a minute.

First: what makes a complete sentence?

Everything rests on this, so it's worth nailing down. A complete sentence needs two things:

• a subject (who or what the sentence is about), and
• a verb (what they do or are),

and it has to make sense standing on its own, with no one needing to ask "and then what?" The dog barked. ✓ That's complete — subject (the dog), verb (barked), and it stands up by itself. Once you can feel whether a group of words can stand alone, you can diagnose all three errors.

The three errors

1. Fragment — a piece, not a whole sentence. It's missing something, or it leaves you hanging:

• ✗ Because it was raining. (because it was raining, WHAT? We're left waiting)
• ✓ Because it was raining, we stayed in.

2. Run-on — two whole sentences jammed together with nothing between them. The reader has to invent the pause:

• ✗ It was raining we stayed in.
• ✓ It was raining. We stayed in.

3. Comma splice — two whole sentences joined with only a comma. A comma is a soft little breath, not strong enough to hold two sentences together:

• ✗ It was raining, we stayed in.
• ✓ It was raining**, so** we stayed in. (add a joining word)

One test for all three: plant a full stop

Here's the single test I want you to run every time. Look at the spot where you're unsure — where you put a comma, or where you put nothing at all. Now imagine planting a full stop right there, and ask two questions: could the words on the left stand alone as a sentence? Could the words on the right?

• If both sides can stand alone, you've got two complete sentences, and you need a proper join between them — a full stop, a joining word (and, but, so), or a semicolon. A lonely comma won't do the job.
• If either side can't stand alone, that weak side is a fragment — don't leave it floating on its own. Attach it to a neighbour, or grow it into a full thought.

That's the entire diagnosis. Everything else is just choosing which join to use.

The three fixes

Once you know what you're looking at, you reach for one of three tools:

• Full stop — cleanest when the two ideas are equally important and you want a clear break: It was raining. We stayed in.
• Joining word — keeps the energy flowing: and, but, so, or. When it joins two whole sentences, pop a comma before it: It was raining, so we stayed in.
• Semicolon — for when the second idea comments closely on the first: It was raining; we stayed in all afternoon.

And a fragment gets a different move altogether. You don't finish it with a full stop, because it can't stand yet. You reattach it to the sentence next door, or you grow it into a complete thought: Because I forgot my kit becomes I got a detention because I forgot my kit.

An important myth to bin: long isn't the same as wrong

Lots of people think any long sentence must be a run-on. Not true. Length is not the crime — two complete thoughts with no proper join is. A long sentence with good joins can be perfectly fine, and sometimes rather good. And the opposite fear — chopping everything into tiny pieces — makes writing sound robotic: We met. We talked. We left. So don't panic about length. Run the full-stop test at the joins, and judge those, not the number of words.

Why it matters

When your sentence boundaries are clean, your reader never has to stop and untangle where one idea ends and the next begins — they just follow your thinking. When the boundaries fail, they stumble, and in an exam that stumble costs marks, because clear sentence boundaries are one of the first things a marker checks. The lovely thing is that one small test — plant a full stop, check both sides — catches all three errors at once. Learn it properly and you've dealt with three of the most-circled mistakes in one go.

Quick check

Fragment, run-on or splice — name it, then fix it:

1. We won the game everyone cheered.
2. After the final whistle.
3. The rain was heavy, we stayed inside.
4. Because my alarm didn't go off.
5. I revised all week the test still felt hard.

Answers

1. Run-on → We won the game. Everyone cheered. (or …game, and everyone cheered.)
2. Fragment → add a main part: After the final whistle, we celebrated.
3. Comma splice → The rain was heavy, so we stayed inside. (or a full stop)
4. Fragment → finish it: Because my alarm didn't go off, I was late.
5. Run-on → I revised all week, but the test still felt hard. (or two sentences)

Where next

• The FANBOYS Comma and Comma Splices — the joining-word fix in full.
• Semicolons and Colons — another way to join two sentences.
• Why Doesn't My Subject Match My Verb? — another sentence-building fix.