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Comma Splices and Run-On Sentences

Understanding & Identifying Comma Splices and Run-Ons

Comma splices and run-ons are major sentence errors that interfere with efficient transmission of thought from writer to reader.

  • A comma splice occurs when only a comma separates two independent sentences.

  • A run-on (or fused sentence) occurs when no punctuation at all separates independent sentences.

Let’s start with two simple sentences:

Tony is dishonest. He steals data for a living.
(In all examples, subjects are bold and verbs are italicized.)

Although this seems pretty straightforward, in the heat of unloading ideas from brain to essay, writers often become lax in clearly indicating where one complete idea ends and where the next begins, as well as how they perceive the relationship between those ideas, often leading to sentence-level errors like these:

COMMA SPLICE:    Tony is dishonest, he steals data for a living.

RUN-ON:    Tony is dishonest he steals data for a living.

As you can see in these two sentences, comma splices and run-on sentences are similar mistakes. In both cases, the punctuation (or lack of it) does not indicate complete, independent sentences.

A comma splice or run-on sentence can also occur when you use transition words:

COMMA SPLICE:    The U.S. Postal Service is usually very reliable, however, sometimes a letter is not delivered for weeks, months, or even years.

Again, there are two independent sentences in the example above. Transition words such as however, therefore, nevertheless, consequently, and then (officially referred to as adverbial conjunctions) do hint at the relationship between ideas; however, they cannot be used alone to connect two sentences.

Corrected versions of the previous sentences could be:

The U.S. Postal Service is usually very reliable; however, sometimes a letter is not delivered for weeks, months, or even years.

The U.S. Postal Service is usually very reliable. However, sometimes a letter is not delivered for weeks, months, or even years.

Avoiding & Correcting Comma Splices and Run-Ons

Four basic methods can be used to avoid or correct comma splices and run-ons:

  1. Separate the independent sentences using a period and capital letter.

Sentence. Sentence.

NO:    Saturday afternoon in Kirkwood is always a busy time everyone seems to be out running errands.
YES:    Saturday afternoon in Kirkwood is always a busy time. Everyone seems to be out running errands.

  1. Join the two sentences into one compound sentence using a comma and coordinating conjunction (for, and, nor, but, or, yet, so):

Sentence, and sentence.

NO:    Communication is important in every relationship, it is especially important to a newly married couple.

YES:    Communication is important in every relationship, but it is especially important to a newly married couple.

  1. Join the two sentences into a compound sentence with a semicolon. The semicolon may be used whether or not the second sentence starts with a transitional word or phrase.

Sentence; sentence.
OR
Sentence; transition, sentence.

NO:    Suddenly, complete silence descended on the boys’ room then the mother knew she’d better check on them.

YES:    Suddenly, complete silence descended on the boys' room; the mother knew she'd better check on them.

YES:    Suddenly, complete silence descended on the boys’ room; then the mother knew she’d better check on them.

  1. Attach a subordinating conjunction to the less important idea, turning it into a dependent clause which, together with the more important idea, creates a complex sentence. The dependent clause can introduce the main idea or add information to the end of it.

Subordinating conjunction+subject/verb, sentence.
OR
Sentence subordinating conjunction+subject/verb.

NO    The surgeon was in complete control of the situation at no time was the patient in danger.

YES    Because the surgeon was in complete control of the situation, at no time was the patient in danger.

YES    At no time was the patient in danger because the surgeon was in complete control of the situation.

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