In English grammar, prepositions are used before a noun, pronoun, or noun phrase to show direction, time, place, location or spatial relationships. They can also introduce an object. First, prepositions in English are considered a fixed class of words, which means new prepositions are rarely added to the English language. Second, prepositions do not have any other form. They cannot be plural, possessive or anything else. Third, most prepositions have many different contextual and natural uses. Fourth, sometimes a preposition works as a noun, an adjective and an adverb. There are around 150 prepositions in English. Here are some common ones: above, about, across, against, along, among, around, at, before, behind, below, beneath, beside, between, beyond, by, down, during, except, for, from, in, inside, into, like, near, of, off, on, since, to, toward, through, under, until, up, upon, with, within