Run-on Sentences and Comma Splices
RUN-ON SENTENCES AND COMMA SPLICES
Run-on sentences can be divided into two types. The first occurs when a writer puts no mark of punctuation and no coordinating conjunction between independent clauses. The second is called a comma splice, which occurs when two or more independent clauses are joined by just a comma and no coordinating conjunction.
Example of a run-on sentence:
The flowers are beautiful they brighten the room. (Incorrect)
Example of a comma splice:
The flowers are beautiful, they brighten the room. (Incorrect)
Examples of correct alternatives:
The flowers are beautiful. They brighten the room.
The flowers are beautiful; they brighten the room.
The flowers are beautiful, and they brighten the room.
The flowers are beautiful because they brighten the room.
A run-on sentence is not defined by its length! The fact that a sentence is very long does not automatically make it a run-on sentence. As you will see, the sentence structure and use of punctuation determine whether a sentence is a run-on.
In order to better understand run-on sentences and comma splices, it is important to review the basics of writing a grammatically correct simple sentence:
A simple sentence is made up of only one independent clause. An independent clause is a group of words that contains a subject and a predicate and forms a complete thought when standing alone. The subject refers to someone or something (the subject contains at least one noun or pronoun). The predicate refers to what the subject does or is (the predicate contains the verb or verbs).Both the subject and predicate can contain additional descriptive elements, such as adverbs, adjectives, prepositions, or other modifying phrases, but in its most basic form the subject is the part of the sentence that contains the noun, and the predicate contains the verb.
A sentence can be complete and correct with one basic independent clause made up of one subject plus its corresponding predicate. To demonstrate the basic structure of a simple sentence, find the noun that forms the subject and divide it from the verb.
| Subject | Predicate | Sentence |
| I | am. | I am. |
| The man | studied. | The man studied. |
| A frog | jumped. | A frog jumped. |
| Lola | sings. | Lola sings. |
By dividing the noun and verb, we can add modifiers to a simple sentence and still see the two basic parts, the subject and the predicate.
| Subject | Predicate |
| The man | studied. |
| The kind man | studied hard. |
| The kind man at the library | studied hard for the test on Friday. |
When looking at the structure of an independent clause, it is helpful to think of all elements of the subject separately from all elements of the predicate. Together the subject and predicate form the two basic and separate parts of each clause.
| Subject | Predicate |
| The kind man and his wife | studied hard for the test and read a book. |
| The man, his wife, and their child | studied hard, read books, and ate dinner. |
If the independent clause forms a complete thought, a period at the end demonstrates that the sentence is complete. The period means STOP. The sentence has ended, and a new sentence will begin.
Run-ons and comma splices occur when more than one subject/predicate pair exists in the sentence. When one subject/predicate pair is followed by an additional subject/predicate pair within one sentence (forming separate independent clauses), they need to be separated (or joined) according to very specific rules of punctuation and grammar.
Look at the following example of a run-on sentence:
The kind man studied hard his wife read a book. (Incorrect)
If we divide the sentence into subject/predicate pairs (each an independent clause), we see that two independent clauses exist, one following the other:
| First independent clause | Second independent clause | ||
| Subject | Predicate | Subject | Predicate |
| The kind man | studied hard | his wife | read a book. |
Without the correct separation, the two independent clauses written together form a run-on sentence. Once you can identify a run-on sentence by its incorrect structure, it is not hard to find a way to correct it.
When two independent clauses appear in one sentence, they must be joined (or separated) in one of four ways:
1.The two clauses can be made into two separate sentences by adding a period.
2.The two clauses can be joined by a comma and a coordinating conjunction (comma plus: and, but, or, nor, for, so, yet).
3.The two clauses can be joined by a semicolon.
4.The two clauses can be rewritten by adding, changing, rearranging, or deleting words. The simplest way to accomplish this is to add a subordinating conjunction between the clauses.
Notice that joining the independent clauses by a comma alone is NOT a choice. When two independent clauses are joined by only a comma, this error is called a comma splice.
The table below demonstrates the four correct options.When two independent clauses appear in a sentence, try to imagine a middle column in which only four possibilities exist to join the two clauses:
| First independent clause | Second independent clause | |||
| Subject | Predicate | 4 CORRECT OPTIONS | Subject | Predicate |
| The kind man | studied hard | .(period) | His wife | read a book. |
| The kind man | studied hard | , and , but , or , for , nor , so , yet (comma plus a coordinating conjunction) | his wife | read a book. |
| The kind man | studied hard | ; (semicolon) | his wife | read a book. |
| The kind man | studied hard | while after as because . . . (examples of subordinating conjunctions -no comma required) | his wife | read a book. |
Please note again that in the above examples a comma alone is NOT one of the correct options.
The kind man studied hard, his wife read a book. (Incorrect)
A comma alone between two independent clauses creates an incorrect comma splice.
Summary (Including Related Grammar Rules)
1. An independent clause contains one subject/predicate pair and expresses a complete thought.
Music makes my life worth living.
| Subject | Predicate |
| Music | makes my life worth living. |
2. A simple sentence is made up of only one independent clause:
Music makes my life worth living.
3. A run-on sentence is made up of two or more independent clauses that are not joined correctly or which should be made into separate sentences. A run-on sentence is defined by its grammatical structure, not its length.
Incorrect: My favorite band is in town they are performing now.
Correct: My favorite band is in town.They are performing now.
Correct: My favorite band is in town, and they are performing now.
4. A comma splice is the incorrect use of a comma to join two independent clauses.
Incorrect: I love classical music, it makes me feel joyful.
Correct: I love classical music because it makes me feel joyful.
Correct: I love classical music; it makes me feel joyful.
5. A compound sentence contains two or more independent clauses that are correctly joined by a comma plus a coordinating conjunction or by a semicolon:
Music means a lot to me, and certain songs bring wonderful memories to mind.
| First independent clause | Second independent clause | |||
| Subject | Predicate | Comma and coordinating conjunction | Subject | Predicate |
| Music | means a lot to me | , and | certain songs | bring wonderful memories to mind. |
Music means a lot to me; certain songs bring wonderful memories to mind.
| First independent clause | Second independent clause | |||
| Subject | Predicate | Semicolon | Subject | Predicate |
| Music | means a lot to me | ; | certain songs | bring wonderful memories to mind. |
6. A comma plus a coordinating conjunction can connect independent clauses correctly. There are seven coordinating conjunctions (sometimes remembered by the acronym "fanboys"):
for, and, nor, but, or, yet, so
7. A complex sentence contains one independent clause and one or more dependent clauses. The dependent clause begins with a subordinating conjunction:
I always think of summer whenever they play that song.
| First independent clause | Second independent clause | |||
| Subject | Predicate | Subordinating conjunction | Subject | Predicate |
| I | always think of summer | whenever | they | play that song. |
8. A subordinating conjunction connects a dependent clause to an independent clause. The dependent clause cannot stand alone; it requires attachment to an independent clause in order to express the complete meaning of the sentence. The following are examples of some of the most common subordinating conjunctions:
after, although, as, as if, because, before, even though, if, in order that, rather than, since, so that, than, that, though, unless, until, when, whenever, where, wherever, whether, while
For more information, please see the following TIP Sheets:
Independent and Dependent Clauses: Coordination and Subordination
Sentence Type and Purpose
