There are two convenient tests to see if you have a sentence fragment: the embedding frame and the tag question. They aren’t foolproof, but they can be useful in a pinch.
- For the embedding frame, simply put the group of words in question at the end of the phrase “I believe that.” For instance, if my sentence is “Roger sang at the concert,” I can say, “I believe that Roger sang at the concert.” This idea makes sense. Now, if my sentence is, “Because the man washed his car,” I would end up with, “I believe that because the man washed his car.” This sentence is a fragment. The idea is incomplete. What happened as a result of the man washing his car?
- For the tag question, simply add “isn’t it?” to the end of your sentence. For example, for the sample sentence “The weather is lovely,” the tag question makes it “The weather is lovely, isn’t it?” This question makes sense. On the other hand, for the sentence fragment “To appreciate the weather,” the tag question makes it “To appreciate the weather, isn’t it?” This question doesn’t make any sense. Most of the time, sentence fragments will become insensible with the tag question, but this isn’t a perfect test. It doesn’t work all the time (sometimes “isn’t it?” has to become “doesn’t it?” or “wouldn’t he?”), but it is a good method to use in conjunction with others.
And here are some more traditional ways of identifying and eliminating sentence fragments.