In grammar, a preposition's a part of speech that introduces a prepositional phrase. For example, in the sentence "The cat sleeps on the sofa", the word "on"'s a preposition, introducing the prepositional phrase "on the sofa". In English, the most used prepositions are "of", "to", "in", "for", "with" and "on". Simply put, a preposition indicates a relation between things mentioned in a sentence. Linguists sometimes distinguish between a preposition, which precedes its phrase, a postposition, whi… (More on Preposition)