A sentence fragment is an incomplete sentence. Sometimes a fragment is missing a subject and/or a verb, like in this sentence:
Waiting for the bus.
Although "waiting" is a verb, it has no subject before it, so we don't know who is waiting for the bus, or if we're just talking about the idea of waiting for the bus. Thus, the thought is incomplete. Some solutions include:
She is waiting for the bus.
You wait for the bus.
Waiting for the bus takes a very long time. (in this case, the action of "waiting for the bus" actually becomes the subject, and "takes" is now the verb).
Other times, a fragment has a subject and a verb, but the thought still isn’t complete. For example:
When I went to the store.
Even though the "I went to the store" part has a subject and a verb and is a complete sentence, adding "when" means that more is needed for the sentence to contain a complete idea:
When I went to the store, I saw Joe.
It was raining when I went to the store.
To avoid sentence fragments, ask yourself:
- Does this sentence have both a subject and a verb?
- Does this sentence have a complete, active idea in it?
- Does this sentence use any connecting words (like "although," "so," "because," "when," "if," "as") that mean the sentence needs two parts to be a complete idea?
A run-on sentence, on the other hand, is a sentence that has too many complete thoughts or ideas that need to be further broken up, either with punctuation, transition words, or a mix of both. For example:
It was raining really hard I ran all the way home.
Both "It was raining really hard" and "I ran all the way home" could be complete sentences on their own, so they need to be separated more clearly. That way, we can tell where each new thought starts, and/or what the relationship between the thoughts is. Here are some options:
1. Put a period: It was raining really hard. I ran all the way home.
2. Put a comma and a conjunction: It was raining really hard, so I ran all the way home.
3. Put a semicolon: It was raining really hard; I ran all the way home.
Identifying the subjects, verbs, and supplemental parts of a sentence is the first step to being able to recognize sentence fragments or run-on sentences. See the Parts of Speech page for more on that, and the handouts linked below for additional examples of fragments and run-on sentences.