What Is a Run-On Sentence?

A run-on sentence occurs when two or more independent clauses (complete thoughts that could each stand alone as a sentence) are joined without the correct punctuation or connecting word. The result is a sentence that keeps going when it should stop - it "runs on" past where it should end.

Run-ons are extremely common in student writing because when ideas flow quickly, writers sometimes forget to separate them properly.

Two Types of Run-On Sentences

1. Fused Sentence

A fused sentence has two independent clauses with no punctuation at all between them.

Run-on: I like dogs they are friendly. Fixed: I like dogs. They are friendly.

2. Comma Splice

A comma splice uses only a comma to join two independent clauses. A comma alone is not strong enough to hold two complete sentences together.

Run-on: I like dogs, they are friendly. Fixed: I like dogs, and they are friendly.

Three Ways to Fix a Run-On Sentence

Period: Split into two separate sentences - I like dogs. They are friendly.

Semicolon: Use a semicolon when the ideas are closely related - I like dogs; they are friendly.

FANBOYS + comma: Add a coordinating conjunction with a comma - I like dogs, and they are friendly.

FANBOYS: For · And · Nor · But · Or · Yet · So

A fourth option for advanced writers: use a subordinating conjunction to make one clause dependent.

Because dogs are friendly, I like them.

Identifying Run-Ons

To check whether a sentence is a run-on:

Find the verb(s). If there are two or more verbs with two separate subjects, you may have two independent clauses.
Read each clause separately. Does each part make sense alone? If yes, they need proper punctuation between them.
Look for comma splices. If a comma is the only thing between two complete thoughts, it is a run-on.

Practice: Read this and decide if it is correct or a run-on:
She ran to the store she needed milk.
✗ Run-on (fused) → Fix: She ran to the store because she needed milk.

Common Student Errors

Students often create run-ons because they:

Write the way they speak (fast, without pauses)
Use then or so without proper punctuation: "We went to the park then we got ice cream" (should have a period or comma + conjunction before then)
Confuse a long sentence with a run-on - a sentence can be long and still be correct if it is properly punctuated

Practice Activities

Give students a paragraph full of run-ons and ask them to fix each one using the method of their choice.
Play "Run-On or Not?" - display a sentence and students signal thumbs up (correct) or thumbs down (run-on).
Have students exchange their own writing with a partner to hunt for run-ons during the editing step.
Write one run-on on the board and challenge students to fix it three different ways (period, semicolon, conjunction).
Use a color-coding system during editing: underline each independent clause in a different color to see where one ends and the next begins.

Frequently Asked Questions

What is a fused sentence?

A fused sentence is a type of run-on where two independent clauses are joined with no punctuation at all. Example: I like dogs they are friendly. There is nothing separating the two complete thoughts.

What is a comma splice?

A comma splice is a run-on where two independent clauses are joined with only a comma, which is not strong enough punctuation. Example: I like dogs, they are friendly. A comma alone cannot join two complete sentences.

What are FANBOYS conjunctions?

FANBOYS is an acronym for the seven coordinating conjunctions: For, And, Nor, But, Or, Yet, So. Adding one of these after a comma correctly joins two independent clauses.