Many people are confused by sentences. They think if they write a sentence that is very short, they will be wrong. They think if they write a sentence that is really long, they will be wrong. What should you do?
Here is an easy way to think of sentences:
A sentence is a unit of thought that contains a subject and a verb. The subject (something) is doing something (the verb).
A fragment is an incomplete sentence. This also means a fragment is an incomplete thought. Usually, either the subject or the verb is missing, so the sentence is not complete. Examples:
The bald eagle, an endangered animal.
(There is no verb—the eagle never does anything!)
Climbing the rocky mountain.
(There is no subject—no one is doing the climbing!)
Remember that a sentence is a unit of thought about something doing something. Also, always proofread to catch this type of common mistake!