A preposition is a word that expresses the relationship of a noun (or pronoun) to the other words of a sentence.

A preposition is used before a noun (or pronoun) to show the relationship of the noun (or pronoun) to the other words of the sentence. 

e.g., in, of, to, at, by, for, with, under, above, into, onto, from, upon, about, behind, besides, before, after, towards, inside, outside, below, around.

Examples.

Words of a sentences	Preposition	Noun or Pronoun
He was standing	at	the door
They were playing	in	the street.
There is a book	on	the table.
She is going	to	college.
She is sleeping	in	the bed.
He was drawing a map	on	a wall.
He was throwing stones	into	the river
They live	in	America.
He goes to school	by	bus.
She opened the lock	with	a key.
They complained	about	the problem.
The meeting was held	in	April.
This shop closes	at	10 PM
This book is written	by	John Keats.

In the above examples, all the prepositions express a relationship of a noun or a pronoun to the other words of the sentence.
Different types of prepositions are used for time, place, direction, agency, device and so on. Some of the examples are as follows:

• Preposition for time. e.g., in, on, at, etc.
• Preposition for place. e.g., in, on, at, etc.
• Preposition for direction. e.g., to, towards, into, through, etc.
• Preposition for agency. e.g., by.
• Preposition for devices, instruments or machines. e.g., on, by, with, etc.

A prepositional phrase, in a sentence, is a group of related words that consists of a preposition and a noun. It is a group of closely linked words that include the preposition and the noun. This means that along with the preposition and the noun, the other words (such as articles: a, an, the) linked to the preposition and noun also become part of the prepositional phrase.

See the following examples where the red part of the sentence is a prepositional phrase.

• The cat was sleeping on a table.
• The kids were playing in the street.
• He was waiting at the door.
• She took out some dresses from the cupboard.
• She wrote something on the page.
• The dog jumped into the river.

The noun within a prepositional phrase is called the object of the prepositional phrase. In the above examples, the nouns table, street, door, cupboard, paper, and river are the objects of prepositional phrases.

Some prepositions are always used with specific verbs, nouns or adjectives. In such a case, using other prepositions instead of them would lead to a grammatical mistake in the sentence or sometimes may change the meaning of the sentence. Such a proposition that must always be used with a specific verb, noun, or adjective is called a dependent preposition.

Example.

• She was laughing at the joker. (correct)
• She was laughing on the joker.  (wrong)
• He was accused of stealing the money. (correct).
• He was accused for stealing the money. (wrong).

  Dependent prepositions for verbs:

See the following examples where the blue word is a verb and the red word is the preposition.

• He is suffering from a high fever.
• I agree with you.
• She belongs to a noble family.
• The students must comply with the rules of the college.
• He is waiting for his friend.
• The police provided us with some information about the thief.
• They were complaining about the problem.

Note. The combination of a verb and the dependent preposition is called a prepositional verb. e.g., suffering from, provide with, agree with.

  Dependent prepositions for adjectives:

See the following examples where the blue word is an adjective and the red word is the preposition.

• I am proud of my son.
• He is ashamed of his bad actions in past.
• I am pleased to see you.
• She was tired of explaining the same thing to everyone.
• He is interested in music.
• Your camera is different from my camera.

  Dependent prepositions for nouns:

See the following examples where the blue word is an noun and the red word is the preposition.

• This is the only solution to your problem.
• A rise in street crimes has been seen this year.
• Eating a balanced diet is the key to good health.
• Due to the lack of resources, they had to stop their business.
• The demand for mobile phones is increasing day by day.

  Note. Some dependent prepositions for verbs may vary according to the type of noun (or pronoun) in a sentence. For instance, the preposition ‘with’ is generally used with the verb ‘agree’ when two or more persons hold the same opinion about something. However, if a person accepts a suggestion or proposal (of another person) to be executed into some action, the preposition ‘to’ is used after the verb ‘agree’. Similarly, if two or more persons accept some terms and conditions applicable to the involved persons, the preposition, ‘on’ is used with the verb ‘agree’.  

• I agree with you that eating sugary foods leads to weight gain.
• The governor agreed to the proposal presented by the people.
• The boss agreed to the recommendations submitted by the employees.
• Both the parties agreed on the terms and conditions.
  
  

Click here to read six types of prepositions in detail.