Sentence fragments, along with run-on sentences, are among the most frequently made sentence errors. A fragment can be defined as a sentence that does not express a complete thought - most often because it is missing a key element, such as a subject or verb, or begins with a subordinating word.
The following examples are all fragments, for different reasons:
Example 1: The attorney objecting to the line of questioning.
The problem with this so-called sentence is that it's missing a verb. Although "objecting" looks like a verb, in this case it's not. Look closely: The phrase "objecting to the line of questioning" is really being used as an adjective to describe "attorney." Which attorney is being discussed? The one who's objecting to the line of questioning.
To make this into a complete sentence, you need to add a verb. If you want to relate a simple, straightforward action, try:
The attorney objected to the line of questioning.
If, however, you wanted to say something more about that attorney, you could write:
The attorney objecting to the line of questioning rose to her feet.
Here, the word "rose" functions as a verb, making this a complete sentence.
Example 2: The jurors remained in the hotel for three days. Bickering the whole time.
While the first sentence here is complete, the second is not - it is missing a subject. The second sentence seems to be an afterthought to the first, so you could link them together:
The jurors remained in the hotel for three days, bickering the whole time.
Or you could add a subject to the second sentence to make it complete:
The jurors remained in the hotel for three days. They were bickering the whole time.
Example 3: Unless the witness testifies.
This sentence is really a dependent (or subordinate) clause that can't stand on its own. If you read it aloud, you're probably thinking, "Unless the witness testifies - WHAT?" The writer here probably meant to attach this clause to the sentence before or after it. The problem could be corrected either way:
This case will be dismissed unless the witness testifies.
Unless the witness testifies, we will surely lose this case.
You can prevent fragments of this sort by making sure that whenever you begin with a subordinating word (such as unless, because, when, if, etc.), you include enough information in the sentence to create a complete thought.
As a general rule, the best way to avoid creating sentence fragments is to ask yourself, when writing a sentence: "Does this sentence, standing on its own, express a complete thought?" If not, check to see what elements are missing.