Sentence Correction

I'm guessing that you haven't gotten a response yet because this question is really too broad to answer in a single post. Just read any newspaper article, and you'll find a dozen prepositions per paragraph, used in a multitude of ways. They often set up modifying phrases, but can modify either nouns or verbs. They are also used frequently in set idiomatic expressions. Depending on the structure of the sentence, we sometimes need to make preposition parallel, and sometimes not.

Is there a specific usage that you have a question about?