What is a “run-on” sentence?

Run-on sentences or "fused sentences" contain two independent clauses incorrectly joined (Hacker 200). While a sentence fragment is an incomplete sentence, a run-on jams together two or more sentences without the correct punctuation (Faigley 579).

Two types of run-on sentences:

Comma splice:

When two independent clauses are connected by a comma, this run-on is called a comma splice (Hult 721).

Example:

I purchased most of what I needed at the store, they were out of bread.

Fused sentence:

When there is no comma, the run-on sentence is fused (Hacker 200).

Examples:

I purchased most of what I needed at the store they were out of bread.

A run-on can be a short sentence. Just because a sentence is long, though, does not necessarily make it a run-on.

Example: Nothing is on television I should turn it off.

The Rules

Ways to avoid a run-on sentence:

Separate the clauses with a semicolon — or a colon or dash, when appropriate (Hacker 202).
Insert a comma and a coordinating conjunction between the clauses (Faigley 581).
Turn one clause into a subordinating clause (Hult 722).
Make the clauses into separate sentences (Hacker 202).

Usage

Semicolon

If the clauses are equally important, use a semicolon to separate them (Hult 723).

I purchased most of what I needed at the store; they were out of bread.

A transitional word might also help sentence flow and clarity (Faigley 581; Hacker 204):

I purchased most of what I needed at the store; however, they were out of bread.

Comma and Coordinating Conjunction

The easiest, and frequently the best, way of correcting the run-on sentence is by using a comma and a coordinating conjuction. There are seven to choose from: for, and, nor, but, or, yet (Hacker 202).

I purchased most of what I needed at the store, but they were out of bread.

Subordinating Clause

Another option would be to subordinate one of the clauses (Hacker 205).

I purchased most of what I needed at the store, although they were out of bread.

Sentences

Simply making each independent clause a sentence also easily fixes a run-on.

I purchased most of what I needed at the store. They were out of bread.

Links

References

Faigley, Lester. The Penguin Handbook. New York: Longman, 2003.
Hacker, Diana. A Writer's Reference. 5th Ed. Boston: Bedford/St. Martin's, 2003.
Hult, Christine A. and Thomas N. Hucklin. The New Century Handbook. 3rd Ed. New York: Longman, 2005.

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