A preposition describes a relationship between other words in a sentence. In itself, a word like "in" or "after" is rather meaningless and hard to define in mere words.
Consider the professor's desk and all the prepositional phrases we can use while talking about it. You can sit before the desk (or in front of the desk). The professor can sit on the desk (when he's being informal) or behind the desk, and then his feet are under the 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 on the desk (if he's really strange). If he's clumsy, he can bump into the desk or try to walk through the desk (and stuff would fall off the desk). Passing his hands over the desk or resting his elbows upon the desk, he often looks across the desk and speaks of the desk or concerning the desk as if there were nothing else like the desk. Because he thinks of nothing except the desk, sometimes you wonder about the desk, what's in the desk, what he paid for the desk, and if he could live without the desk. You can walk toward the desk, to the desk, around the desk, by the desk, and even past the desk while he sits at the desk or leans against the desk.
All of this happens, of course, in time: during the class, before the class, until the class, throughout the class, after the class, etc. And the professor can sit there in a bad mood [another adverbial construction].

List of common prepositions



Is it any wonder that prepositions create such troubles for students for whom English is a second ********? We say we are at the hospital to visit a friend who is in the hospital. We lie in bed but on the couch. We watch a film at the movies but on television. For native speakers, these little words present little difficulty, but try to learn another ********, any other ********, and you will quickly discover that prepositions are troublesome wherever you live. This page contains some interesting (sometimes troublesome) prepositions with brief usage notes.


Prepositions of Time: at, on, and in
IN
Use 'in' months and years and periods of time:
• in January
• in 1978
• in the twenties
Use 'in' a period of time in the future:
• in a few weeks
• in a couple of days
AT
Use 'at' with precise time:
• at six o'clock
• at 10.30
• at two p.m.
ON
Use 'on' with days of the week:
• on Monday
• on Fridays
Use 'on' with specific calendar days:
• on Christmas day
• on October 22nd
IMPORTANT NOTES
in the morning / afternoon / evening - at night
We say in the morning, afternoon or evening BUT we say 'at night'

Prepositions of Place: at, on, and in
IN
Use 'in' with spaces:
• in a room / in a building
• in a garden / in a park
Use 'in' with bodies of water:
• in the water
• in the sea
• in a river
Use 'in' with lines:
• in a row / in a line
• in a queue
AT
Use 'at' with places:
• at the bus-stop
• at the door
• at the cinema
• at the end of the street
Use 'at' with places on a page:
• at the top of the page
• at the bottom of the page
Use 'at' in groups of people:
• at the back of the class
• at the front of the class
ON
Use 'on' with surfaces:
• on the ceiling / on the wall / on the floor
• on the table
Use 'on' with small islands:
• I stayed on Maui.
Use 'on' with directions:
• on the left
• on the right
• straight on
IMPORTANT NOTES
In / at / on the corner
We say 'in the corner of a room', but 'at the corner (or 'on the corner') of a street'
In / at / on the front
• We say 'in the front / in the back' of a car
• We say 'at the front / at the back' of buildings / groups of people
• We say 'on the front / on the back' of a piece of paper



Prepositions of Movement: to
and No Preposition
We use to in order to express movement toward a place.
They were driving to work together.
She's going to the dentist's office this morning.
With the words home, downtown, uptown, inside, outside, downstairs, upstairs, we use no preposition.
Grandma went upstairs
Grandpa went home.
They both went outside.
Prepositions of Time: for and since
We use for when we measure time (seconds, minutes, hours, days, months, years).
He held his breath for seven minutes.
She's lived there for seven years.
The British and Irish have been quarreling for seven centuries.
We use since with a specific date or time.
He's worked here since 1970.
She's been sitting in the waiting room since two-thirty.


Prepositions with nouns, adjectives, and verbs.
Prepositions are sometimes so firmly wedded to other words that they have practically become one word. (In fact, in other ***************, such as German, they would have become one word.) This occurs in three categories: nouns, adjectives, and verbs.



A combination of verb and preposition is called a phrasal verb. The word that is joined to the verb is then called a particle.
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
Unnecessary Prepositions
In everyday speech, we fall into some bad habits, using prepositions where they are not necessary. It would be a good idea to eliminate these words altogether, but we must be especially careful not to use them in formal, academic prose.

• She met up with the new coach in the hallway.
• The book fell off of the desk.
• He threw the book out of the ********
• She wouldn't let the cat inside of the house. [or use "in"]
• Where did they go to?
• Put the lamp in back of the couch. [use "behind" instead]
• Where is your college at?



All the best .
Kassim