In simplest terms, prepositional phrases consist of a preposition and an object of a preposition. Prepositions are<"> indeclinable words that introduce the object of a prepositional phrase. Indeclinable words are words that have only one possible form. For example, below is a preposition, but belows or belowing are not possible forms of below.

The noun phrase or pronoun that follows the preposition is called the object of the preposition. For example, behind the couch is a prepositional phrase where behind is the preposition and the noun phrase the couch acts as the object of the preposition. Sometimes adjectives are used to further modify the object of the preposition, as in behind the big old smelly green couch.

Formal Functions of Prepositions

Prepositions perform three formal functions in sentences. They can act as an adjective modifying a noun, as an adverb modifying a verb, or as a nominal when used in conjunction with the verb form to be.

Prepositions Functioning as Adjectives

In the following sentences, prepositional phrases perform the function of modifying the nouns boat, pen, and car:

Look at the boat with the blue sail. Please hand me the pen next to the telephone. Park the car beside the fence.

Prepositions Functioning as Adverbs

In these examples, notice how the prepositional phrases perform adverbial functions by modifying the verbs after, stalled, and won:

The coyote runs after the rabbit. The car stalled despite the tune-up. The team won without the starting quarterback.

Prepositions Functioning as Nominals

In English, sometimes words function as nouns but aren't themselves nouns. These words are called nominals. Prepositions sometimes perform this important function in sentences when they are used in conjunction with the verb to be. For example:

The park is next to the hospital. The student is between an A and a B. The fight scene is before the second act.

Semantic Properties of Prepositions

In semantic terms, the preposition functions to illustrate a logical, temporal, or spatial relationship between the object of the prepositional phrase and the other components of the sentence. Consider the following examples:

The dog is asleep on his bed.

In this example, the prepositional phrase on his bed indicates a spatial relationship between the subject dog and the object bed. If the preposition on was replaced with under or beneath the spatial relationship would be altered.

The town hasn't been the same since the war.

In this sentence, the prepositional phrase since the war indicates a temporal relationship between the verb phrase hasn't been the same and the object war.

The family survived despite the accident.

he prepositional phrase despite the accident in this sentence indicates a logical relationship between the survival of the family and the accident.

List of Common Prepositions

The following table lists the most commonly used prepositions in English.

• about
• above
• across
• after
• against
• along
• among
• around
• at
• before
• behind
• below
• beneath
• beside
• between
• beyond
• but
• by
• despite
• down
• during
• except
• for
• from
• in
• inside
• into
• like
• near
• off
• of
• on
• onto
• out
• outside
• over
• past
• since
• through
• throughout
• till
• to
• toward
• under
• underneath
• until
• up
• upon
• with
• within
• without     

Responsible Use

There are no rules that govern how much nouns and verbs can be modified in English. Often writers employ prepositional phrases excessively, creating an almost comical effect in an attempt at over clarification. The following sentence implements a string of propositional phrases to modify the verb stood.

The old farmhouse stood for years, after the revolution, by the fork in the road, beyond the orange grove, over the wooden bridge, at the farthest edge of the family's land, toward the great basin, down in the valley, under the old mining town, outside the city's limits, and past the end of the county maintained road.

Prepositional phrases, in theory, can modify sentences infinitely. Therefore, it is important for writers to understand their form and function in order to make appropriate stylistic choices.

A preposition is a word which shows relationships among other words in the sentence.  The relationships include direction, place, time, cause, manner and amount.  In the sentence She went to the store, to is a preposition which shows direction.  In the sentence He came by bus, by is a  preposition which shows manner.  In the sentence They will be here at three o'clock, at is a preposition which shows time and in the sentence It is under the table, under is a preposition which shows place.

A preposition always goes with a noun or pronoun which is called the object of the preposition.  The preposition is almost always before the noun or pronoun and that is why it is called a preposition.  The preposition and the object of the preposition together are called a prepositional phrase.  The following chart shows the prepositions, objects of the preposition, and prepositional phrases of the sentences above.
 

Preposition	Object of the Preposition	Prepositional Phrase
to	the store	to the store
by	bus	by bus
at	three o'clock	at three o'clock
under	the table	under the table

Prepositional phrases are like idioms and are best learned through listening to and reading as much as possible.   Below are some common prepositions of time and place and examples of their use.

Prepositions of time:
at two o'clock
on Wednesday
in an hour, in January; in 1992
for a day

Prepositions of place:
at my house
in New York, in my hand
on the table
near the library
across the street
under the bed
between the books

1)  Which does a preposition come before?