Problematic 'sentences': To write a correct sentence, you need to have a good understanding of what a sentence is. Students who don't have this understanding, or don't take care, often include problem sentences in their writing. Native English speakers are just as likely to write problem sentences as ESL students. There are three main types of problem sentence:
Run-on sentences: These are two sentences that the writer has not separated with an end punctuation mark, or has not joined with a conjunction. (Click the following run-ons to see where they should be separated into two sentences.)
I went to Paris in the vacation it is the most beautiful place I have ever visited.
It's never too late to learn to swim you never know when you may fall from a boat.
If you're going to the shops can you buy me some eggs and flour I want to make a cake.
I like our new math teacher, she always explains the work very clearly.
He was late to school again, his bus got caught in heavy traffic.
Advice: It is helpful to read your written work aloud. When you speak, you will make natural pauses to mark the end of your sentences or clauses. If there is no corresponding end punctuation mark in your writing, you can be almost certain that you have written a run-on sentence.
Sentence fragments: Fragment sentences are unfinished sentences, i.e. they don't contain a complete idea. A common fragment sentence in student writing is a dependent clause standing alone without an independent clause. In the each of the following examples the fragment is the second 'sentence', shown in red: