Generally speaking, a Preposition tells you where something is or when something happened:

at, in, on, by…

As you might guess, a Prepositional Phrase simply means a preposition and what it is talking about known as the object:

{preposition} + {object}

by + the light of the silvery moon

in + the nick of time

different objects

The object is most often a noun, pronoun or gerund:

at (prep.) school (noun)

with (prep.) us (pronoun)

by (prep.) driving (gerund)

about (prep.) what you said (noun clause)

Apart from a preposition and its object, prepositional phrases can also include modifiers related to either the object or the preposition.

from (prep.) my (modifier) garden (noun)

in (prep.) the old (modifiers) testament (noun)

under (prep.) the old chestnut (modifiers) tree (noun)

by (prep.) working (gerund) hard (modifier)

Adjectives or Adverbs?

Prepositional phrases are used as adjectives or adverbs.

Here they are adverbs and they tell us how, when or where something happens.

I saw them under the bed.

Let’s meet at midnight.

Almost half my plants died from frost bite last winter.

After work, we all went for a pint!

Let’s meet up at Susan’s place.

NB a quick way to decide whether a prepositional phrase is acting as an adverb is by seeing if it answers the question: how, when or where something happens.

And here they are adjectives and they describe:

The boy on the bus was shouting loudly on the phone.

The plates in the sink can go in the dishwasher.

Who took the dictionary on the top shelf?

The team from Russia flew in last night.

NB a quick way to decide whether a prepositional phrase is acting as an adjective is by seeing if it answers the question: which one(s)?

Prepositional Phrases & TEFL

Is it worth explaining to your class that prepositional phrases can be adjectives or adverbs?

Probably not. Keep that one to yourself.

On the other hand, do try to teach prepositional phrases as a whole; it’s useful for your students to learn them as template phrases rather than break them down too much.

Useful Links

Prepositions‏‎ in English Grammar – a look at prepositions in general