Which sentence is the right one and why: "Service object through which asynchronous operations are dispatched" or "Service object which asynchronous operations are dispatched through". Please explain when is it allowed to put prepositions at the end of a sentence?

  • These sentences don't sound complete to me Dec 20, 2016 at 10:32
  • This is a documentation block of a variable in a programming language. Whether the sentence is complete or not does not matter in this case I think. I'd just like to know the rules for using prepositions. Dec 20, 2016 at 10:36
  • For example why is it possible to put a preposition at the end of a question, like "What are you looking for?" Dec 20, 2016 at 10:38
  • 3
    en.oxforddictionaries.com/grammar/… may help with that Dec 20, 2016 at 10:39
  • The first part of your question on which sentence is correct depends on the rest of the sentence. Either could be correct. Dec 20, 2016 at 10:44

1 Answer 1


The idiomatic spoken version is:

... the service object (that) async operations are dispatched through...

It has a potentially reduced clause and a postponed preposition, and it drops the relative pronoun which.

The more formal written version is:

... the service object through which asynchronous operations are dispatched...

A small percentage of speakers are such practiced writers that they will use the second version even when speaking. But they are the exception, not the rule.

A simpler way to state it is to avoid the passive:

.. the service object which dispatches asynchronous operations...

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