A run-on is when two sentences are "combined," or "run together" without the necessary connecting words or punctuation (or both of these!).

How to Identify a Run-on?

If two sentences are written together without any punctuation at all, this is a fused sentence.

For example:

This is a fused sentence because there is no period between the two sentences.

Marie got As on her report card her parents took her out to dinner.
Marie got As on her report card. Her parents took her out to dinner.

If we add a period, we get two complete sentences.

If two sentences are combined using only a comma, without a connecting word (such as "and, but, or, nor, for, so, yet"), this is called a comma splice.

For example:

This is a comma splice sentence.

Halloween is next week, I'm going to eat so much candy.
Halloween is next week, and I'm going to eat so much candy.

If we add a connecting word, we get one complete sentence.

How to Correct a Run-on?

1. Put a period between the two sentences.

For example:

This is a run-on.

Lisa was extremely sick she had to go to the hospital.
Lisa was extremely sick. She had to go to the hospital.

Now these are two good sentences.

2. Connect the two sentences with a comma and a coordinating conjunction (and, but, nor, for, so, or, yet). This forms a compound sentence.

For example:

This is a run-on.

It's raining we don't want to go outside.
It's raining, so we don't want to go outside.

This is a good sentence.

3. Connect the two sentences with a semicolon.

For example:

This is a run-on.

The diving board is fun the slide is even better!
The diving board is fun; the slide is even better!

This is a good sentence.

4. Connect the two sentences with a semicolon and a word or phrase to explain the relationship between the two sentences (however, therefore, then, as a result, consequently, also, in contrast, nevertheless, on the other hand, etc.).

For example:

This is a run-on.

Sarah is a good driver she got in an accident.
Sarah is a good driver; nevertheless, she got in an accident.

This is a good sentence.

5. Connect the two sentences by inserting one as a dependent clause. You will often use a dependent clause signal word to do this (because, if, although, which, who, when). This forms a complex sentence.

For example:

This is a run-on.

Grandma is coming at noon she is bringing my birthday cake!
Grandma, who is bringing my birthday cake, is coming at noon!

This is a good sentence.

Summary

A run-on is when two sentences are "combined," or "run together" without the necessary connecting words or punctuation (or both of these!).
How to identify a run-on:
- If two sentences are written together without any punctuation at all, this is a fused sentence.
- If two sentences are combined using only a comma, without a connecting word (such as "and, but, or, nor, for, so, yet"), this is called a comma splice.
We can correct run-on in the following ways:
- Put a period between the two sentences.
- Connect the two sentences with a comma and a coordinating conjunction. This forms a compound sentence.
- Connect the two sentences with a semicolon.
- Connect the two sentences with a semicolon and a word or phrase to explain the relationship between the two sentences.
- Connect the two sentences by inserting one as a dependent clause. This forms a complex sentence.