A preposition is a word used to link a noun or pronoun (its object) to another sentence element by expressing such relationships as direction (to, into, across, toward), location (at, in, on, under, over, beside, among, by, between, through), time (before, after, during, until, since). Prepositions show the relationship of a noun or pronoun to some other word in the sentence. In the following sentences, the prepositions are shown in boldfaced type. The words related by the preposition are in italics. Note that the sentences are alike in wording except for the prepositions across, inside, and around. The change in relationship between ran and yard is due to the change of preposition.
A preposition always introduces a phrase. (A phrase is a group of related words used as a single part of speech and not containing a verb and its subject.) A prepositional phrase is a group of words beginning with a preposition and usually ending with a noun or a pronoun.
• in the laboratory before the class
• under the table along the street
The object of a preposition (the word or phrase following it) is always in the objective case. The noun or pronoun that ends the phrase is the object of the preposition that begins the phrase. Prepositional phrases do not stand by themselves. They are parts of a sentence and are used as modifiers, sometimes as adjectives and at other times as adverbs. When the object is a compound noun, both nouns should be in the objective case. For example, the phrase “between you and me”is frequently and incorrectly written as “between you and I.” Me is the objective form of the pronoun, and I is the subjective form.
Many words that function as prepositions also function as adverbs. If the word takes an object and functions as a connective, it is a preposition; if it has no object and functions as a modifier, it is an adverb.
PREPOSITIONS :The manager sat behind the desk in her office.
ADVERBS :The customer lagged behind; then he came in and sat down.
Luis Alberto Viades Valenci. 2002. Teaching Technical English Writing