Prepositions are simple words, but they are not as easy to use as they appear to be. If used wrongly, they become adverbs or conjunctions and convey different meaning.

A preposition is followed by a noun or a pronoun.
We go jogging every day after work. (Preposition)
(The preposition is after and is followed by the noun work.)
An adverb comes after a verb and is not followed by an object.
We got here not so long ago and she arrived after. (Adverb)
(Afteris an adverb that comes after the verb arrived.)
A conjunction has a clause that comes after it.
We arrived after he had left. (Conjunction)
(The clause he had left comes after the conjunction after.)


More examples:

Using the preposition until:

  • She was up until three o'clock watching the movie. (Preposition)
  • He stayed there until the rain stopped. (Conjunction)

Using the preposition as:

  • She's got a job as a horse trainer. (Preposition)
  • The husband was fat, and his wife was just as fat. (Adverb)
  • We watched as he was flying his kite. (Conjunction)

Using the preposition but:

  • He didn't tell anyone but his lawyer. (Preposition)
  • We have but one week to meet the deadline. (Adverb)
  • You are not only my best friend but also my business partner. (Conjunction)

Using the preposition round:

  • We walked round the marketplace. (Preposition)
  • They gathered round to listen to his encounter with a wild pig. (Adverb)
  • In that tree, I saw two big, round eyes which must be the owl's. (Adjective)

Using the preposition inside:

  • Beautiful pictures can be found inside the book. (Preposition)
  • The book has beautiful pictures inside. (Adverb)
  • The inside pages of the book have beautiful pictures. (Adjective)
Some more words:
Words used as prepositions, adverbs, or adjectives: inside, outside, past, round.
Words used as prepositions, adverbs, or conjunctions: after, as, before, but, since.