A sentence must express a complete thought. The length of the sentence is not important—it may be very long or very short, but it must make sense by itself.

Sometimes writers mistakenly believe that a long sentence is too long and divide it in two, creating an error called a sentence fragment.

What is a sentence fragment?

If you drop a glass vase on the floor, usually it shatters into pieces. Each of those pieces is a fragment, an incomplete piece of the whole.

In grammar, the term sentence fragment refers to an incomplete group of words punctuated as a sentence. Often, the fragment has been broken off from the sentence before or after it, and you can fix it simply by re-attaching it. At other times, you may need to add or remove words to turn a fragment into a complete sentence.

What kind of word groups are common fragments?

Most fragments are phrases, dependent clauses or mixed constructions.

Phrases

A phrase or a series of phrases may contain several words. But the word group cannot express a complete thought because it lacks something essential to a sentence: a subject or a verb, or both. In the examples below, the fragments are in italics:

• Verb phrase (lacks a subject):
  • Fragmented: The sudden wind pounced on the piles of leaves. And scattered them across the neatly raked lawn.
  • Revised: The sudden wind pounced on the piles of leaves and scattered them across the neatly raked lawn.
• Noun phrase (lacks a verb):
  • Fragmented: We saw a performance by Natasha Ivanovna. A ballerina related to my husband's family.
  • Revised: We saw a performance by Natasha Ivanovna, a ballerina related to my husband's family.
• Absolute phrase (may contain a verbal but lacks a verb):
  • Fragmented: His work finally done. Ali relaxed with a movie.
  • Revised: His work finally done, Ali relaxed with a movie.
• Series of verbal phrases (lacks a subject and a verb):
  • Fragmented: Looking like modelling clay shaped into landscapes. Cloud banks drifted lazily across the sky.
  • Revised: Looking like modelling clay shaped into landscapes, cloud banks drifted lazily across the sky.
• Series of prepositional phrases (lacks a subject and a verb):
  • Fragmented: The stream flowed swiftly along. Over the rocks and boulders in its path and through the thirsty fields.
  • Revised: The stream flowed swiftly along over the rocks and boulders in its path and through the thirsty fields.

Dependent clauses

Unlike a phrase, a dependent clause contains a subject and a verb. But it does not express a complete thought. To make sense, it must be connected to an independent clause (a simple sentence):

• Adjective clause:
  • Fragmented: I need to write a thank-you note to Aunt Maude. Who sent me the turtle-shaped soup tureen.
  • Revised: I need to write a thank-you note to Aunt Maude, who sent me the turtle-shaped soup tureen.
• Adverb clause:
  • Fragmented: Because we didn't have enough paper for the new printer. We had to make a quick trip to the store.
  • Revised: Because we didn't have enough paper for the new printer, we had to make a quick trip to the store.
• Series of dependent clauses:
  • Fragmented: After we left the campsite where we had stayed for a week. We drove on to Toronto for the Exhibition.
  • Revised: After we left the campsite where we had stayed for a week, we drove on to Toronto for the Exhibition.
  • Fragmented: Motorists taking this route are at risk. If they don't know that there is a hairpin turn down the road.
  • Revised: Motorists taking this route are at risk if they don't know that there is a hairpin turn down the road.

Mixed constructions

A mixed construction is a "sentence" made up of mismatched parts. One very common example is a prepositional phrase followed by a verb. The writer is trying to use the object of the preposition as the subject of the verb. But the object can't do double duty, so the word group ends up as a fragment, without a subject.

• Fragmented: By working out often will keep you in shape. (No subject for verb will keep; working out often is object of preposition By.)
  
  
  • Solution 1: Drop the preposition By.

    Working out often will keep you in shape.

  • Solution 2: Add the subject you and reword.

    By working out often, you can keep in shape.

How can I tell if I have written a fragment?

Sentence fragments can be hard to detect, since they usually sound all right when you read them together with the surrounding sentences. Here's a trick: starting from the end of the paragraph, read each "sentence" aloud on its own. Usually the fragments won't sound complete, and you will be able to pick them out more easily.