The purpose of a preposition is to show the relationship of the object of the preposition to the rest of the sentence. Following is a list of words that are commonly used as prepositions:
The pen was on the desk.
The pen was in the desk.
The pen was under the desk.
The pen was above the desk.
He met his colleagues before the meeting.
He met his colleagues after the meeting.
He met his colleagues during the meeting.
In the two sets of examples above, prepositional phrases are used to indicate the relationship between the preposition, the object of the preposition, and the rest of the sentence.
Some words that can be used as prepositions can also be used as adverbs or conjunctions. In order for a word to be a preposition, it must have an object. Otherwise, it is not a preposition.
They asked us to let them know when we were through with our meeting.
He said that the convention would be held mostly outside.
I asked her to take out the trash.
Will you please help us clean up?
The closet inside the room smelled of mold. (Conjunction)
He decided to walk inside the house. (Preposition)
They saw that beneath the table was an umbrella. (Conjunction)
The dog likes to sleep beneath the bed. (Preposition)
When a pronoun follows the preposition, it must be in the object form. The object pronouns are:
I believe that Mr. Jensen was talking to her.
Do you know when Luke will meet with us?
We have not heard from them yet.
Between you and me, any idea is better than his last one.
(Remember that whenever the preposition between is used, the object form of the pronoun must follow it.)
Please let Frank and Janice know that the gift is from them and us.
Are you planning to come with him and me?
We went to the park with them.
They could not learn anything from him.
I believe they will arrive before us.
To whom were you talking?
From where is he?
She just wanted someone with whom to read.
Whom were you talking to?
Where is he from?
She just wanted someone to read with.
In very formal writing, readers may object to sentences that end with a preposition. But for most cases, simply use the order that seems most natural.