Very often the subject of the sentence is missing. The following sentence fragment does not tell who it is that the writer is talking about. The sentence can be completed by adding the subject The president.
Met with the people. (This is a sentence fragment - missing subject)
The president met with the people. (This is a complete sentence)
Sometimes the predicate is missing. The following sentence fragment does not have a predicate. The sentence can be completed by adding the predicate was loud..
The sound from the room. (This is a sentence fragment - missing predicate)
The sound from the room was loud. (This is a complete sentence)
In some cases, sentence fragments may have a subject and a verb, but it does not form a complete thought.
Because he lost his car keys.
After they finished dinner.
Since you were not at home.
All the above sentence fragments are not able to stand on their own. They are called dependent clauses or subordinate clauses. We can complete the sentences by adding more information - independent clauses.
Because he lost his car keys, he had to catch the bus home. (He had to catch the bus home because he lost his car keys.)
After they finished dinner, they went to the movies. (They went to the movies after they finished dinner.)
Since you were not home, I left a note at your door. (I left a note at your door since you were not home.)
John completed the job. (sentence)
Unless John completed the job. (fragment)
John, who completed the job. (fragment)
Complete Sentences and Fragments.
Each group of words below is a fragment. Tell whether the subject or predicate is missing.
Sentence Skills (Recognizing Fragments)
This video will help you figure out whether a sentence is truly a complete sentence.