Simply put, a preposition links nouns, pronouns and phrases to other words in a sentence. There are about 150 prepositions in English. Yet this is a very small number when you think of the thousands of other words (nouns, verbs etc). Prepositions are important words. We use individual prepositions more frequently than other individual words. In fact, the prepositions of, to and in are among the ten most frequent words in English.