The preposition is a part of speech that denotes the relations between objects and phenomena. It shows the relations between a noun or a pronoun and other words.

Usually, the preposition is not stressed and stands before the word it refers to.

Desert moved quickly to the windows. (Galsworthy)

Sometimes, however, a preposition may be separated from the word it refers to and placed at the end of the sentence or clause. In that case, it is stressed.

But he sounds as though he knows what he’s talking about. (Wilson)

The proposition may be weakly stressed before a pronoun.

She wrote the words to them herself, and in other poems. (Galsworthy)

The proposition is stressed when its meaning is emphasized.

The book was in the table, not on it.