Grammar: Groups & phrases: Prepositional phrases: Further reading

Moving the preposition

Sometimes the preposition of a prepositional phrase is 'deferred', ie it is separated from the noun group forming the prepositional phrase. Such deferred prepositions may occur in several types of construction:

Passive voice clauses

Prepositions commonly occur on their own in passive voice clauses while in the equivalent active voice clause the preposition occurs as part of a prepositional phrase:

Has the room been paid for? [passive clause]
Has someone paid for the room? [active clause]

Has the room been paid for by Mr Smith? [passive clause]
Has Mr Smith paid for the room? [active clause] 

The prepositional phrase in both these examples is for the room, with the preposition for separated from the noun group the room in the passive voice clause. (Has the room been paid for by Mr Smith? has two prepositional phrases: by Mr Smith, for the room.) 

For more information on passive voice clauses, see Grammar: Groups & phrases: Verb group: Structure of the verb group: Voice: active and passive

Non-finite clauses

Prepositions commonly occur on their own in clauses which include a non-finite clause, either with the verb in the -ing form or as to infinitive:

-ing form

This programme is worth listening to. [this programme = Theme ]
It is worth listening to this programme. [it = Theme]

to-infinitive

My brother is impossible to work with. [my brother = Theme]
It is impossible to work with my brother. [it = Theme]

The function of this structure is to make the noun group in the prepositional phrase (to this programme, with my brother) the Theme in the clause rather than the 'dummy' it. 

Interrogative clauses and non-defining relative clauses

Prepositions commonly occur on their own in interrogative clauses and in non-defining relative clauses, using wh- words and relative pronouns (which, whose, where). However, there are usually two versions possible, one formal and one informal:

interrogative clause

At which station did you board the train? [formal]
Which station did you board the train at? [informal]

defining relative clause

The movie about which Tom was telling you yesterday. [formal]
The movie (which) Tom was telling you about yesterday. [informal]

The formal version using the full prepositional phrase is much more common in writing than in speech. 

In some cases a prepositional phrase with the preposition preceding the noun is not possible:

What did she look like?
All she could talk about was her new boyfriend.

Sentences such as these can only have a normal prepositional phrase by rewording them:

All she could talk about was her new boyfriend. [prepositional phrase with 'deferred' preposition]
She could only talk about her new boyfriend. [normal prepositional phrase]

For more information on interrogative clauses and relative clauses, see:

Grammar: Clause: Using clauses to interact: Overview

Which prepositions are likely to occur on their own?

The most common prepositions can generally occur on their own, especially those expressing 'place' in the sense of 'location': 

	place: location
		He left his bag in the taxi.  The taxi he left his bag in (returned after a few minutes).

For more information on prepositions, see Grammar: Word classes: Prepositions: Overview