Words that are sometimes conjunctions can act as prepositions.

The subordinating conjunctions BEFORE, AFTER and UNTIL can act as prepositions when they are followed by objects rather than dependent clauses.

• Remember that a clause has a subject and a verb. A prepositional phrase does not.

PREPOSITION

• Charlie will wait here until sunset.
  • UNTIL connects the object of the preposition SUNSET with the clause.
    • NOTE: The entire prepositional phrase is an adverb, not one word.
      
      
• It will be some time before summer.
  • BEFORE connects the object of the preposition SUMMER with the clause.
    
    
• After that effort, everyone doubts whether she can win.
  • AFTER THAT EFFORT is an adverbial phrase and AFTER is a preposition.
    

CONJUNCTION

• Charlie will wait here until we finish the test.
  • UNTIL connects the independent clause to the dependent clause.
    • NOTE: CHARLIE WILL WAIT is connected to WE FINISH.
      
      
• It will be some time before the seasons change.
  • BEFORE connects the IT WILL BE to SEASONS CHANGE.
    
    
• After she did so badly, everyone doubted whether she could win.
  • AFTER connects SHE DID with EVERYONE DOUBTED.

To begin studying correlative conjunctions, please turn the page.