A preposition describes a relationshipbetween other words in a sentence. Initself, a word like "in" or "after" is rathermeaningless and hard to define in merewords.For instance, when you do try to define apreposition like "in" or "between" or"on," you invariably use your hands toshow how something is situated inrelationship to something else.
Prepositions are nearly always combined withother words in structures called prepositionalphrases.Prepositional phrases can be made up of a milliondifferent words, but they tend to be built thesame: a preposition followed by a determiner andan adjective or two, followed by a pronoun ornoun (called the object of the preposition).This whole phrase, in turn, takes on a modifyingrole, acting as an adjective or an adverb, locatingsomething in time and space, modifying a noun, ortelling when or where or under what conditionssomething happened.
Consider the professors deskYou can sit before the desk (or in front of the desk).The professor can sit on the desk (when hes beinginformal) or behind the desk, and then his feet are underthe desk or beneath the desk.He can stand beside the desk (meaning next to the desk),before the desk, between the desk and you, or even onthe desk (if hes really strange).If hes clumsy, he can bump into the desk or try to walkthrough the desk (and stuff would fall off the desk).Passing his hands over the desk or resting his elbowsupon the desk, he often looks across the desk and speaksof the desk or concerning the desk as if there werenothing else like the desk.
Because he thinks of nothing except the desk,sometimes you wonder about the desk, whats inthe desk, what he paid for the desk, and if he couldlive without the desk.You can walk toward the desk, to the desk, aroundthe desk, by the desk, and even past the desk whilehe sits at the desk or leans against the desk.All of this happens, of course, in time: during theclass, before the class, until the class, throughoutthe class, after the class, etc. And the professor cansit there in a bad mood.
You may have learned that ending a sentence with apreposition is a serious breach of grammatical etiquette.It doesnt take a grammarian to spot a sentence-endingpreposition, so this is an easy rule to get caught up on (!).Although it is often easy to remedy the offendingpreposition, sometimes it isnt, and repair effortssometimes result in a clumsy sentence. "Indicate thebook you are quoting from" is not greatly improved with"Indicate from which book you are quoting."Based on shaky historical precedent, the rule itself is alatecomer to the rules of writing. Those who dislike therule are fond of recalling Churchills rejoinder: "That isnonsense up with which I shall not put." We should alsoremember the childs complaint: "What did you bringthat book that I dont like to be read to out of up for?"
Idiomatic Expressions with Prepositions• agree to a proposal, with a person, on a price, in principle• argue about a matter, with a person, for or against a proposition• compare to to show likenesses, with to show differences (sometimes similarities)• correspond to a thing, with a person• differ from an unlike thing, with a person• live at an address, in a house or city, on a street, with other people