Why do we say "In which" in many formal essays and documents? I never understood this. The definition for which on Merriam Webster is "being what one or ones out of a group". Why is it that we have adapted to using the word 'which' outside of interrogative sentences?

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    Because which is used as a relative pronoun at least as often as it is used as an interrogative pronoun. As for in which it's formal language and helps mark the style. It's not much used in speech, which means it's not very important. Other prepositions occur, though; the technical term in syntax is "Pied-Piping". Commented Sep 22, 2015 at 2:30
  • We haven't "adapted" to using "'which' outside of interrogative sentences." Both the relative and interrogative uses come to us from Old English. Which is to say that the dual usage is very old, over a thousand years, going back to the origins of language.
    – deadrat
    Commented Sep 22, 2015 at 2:37
  • In older (Victorian?) era novels it was common for the chapters instead of having titles to have a short synopsis beginning with "in which...". For example, chapter 3 might be the chapter "in which Johnny discovers his long-lost aunt". This fits your definition well, since we are describing what makes this chapter unique out of the group of all the chapters in the book. When you see this construction in contemporary writing, its usually an allusion to this old-fashioned way of introducing book chapters.
    – The Photon
    Commented Sep 22, 2015 at 3:05
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    If Merriam Webster could not make it clear to you that "which" is used in questions and in relative clauses, you should use other dictionaries too. Perhaps a grammar wouldn't be bad.
    – rogermue
    Commented Sep 22, 2015 at 5:27
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    Without some examples your question is invalid. (I can't believe it wasn't closed two years ago.)
    – Hot Licks
    Commented Oct 29, 2017 at 23:59

1 Answer 1


Why do we say "In which"...?

...because "in which" is very much a part of written and spoken English, whether formal or informal. It is simply a prepositional phrase composed of the preposition "in" and the relative pronoun "which." It can be used to mean "where" or "that." Therefore, it can be replaced by the latter two. If you are not comfortable using "in which" try replacing it with where or that, whichever is applicable.


  • This is the room 'in which' the supplies were stocked.
  • This is the room where in the supplies were stocked.
  • The town 'in which' I spent my childhood years is now urbanized.
  • The town where I spent my childhood years in is now urbanized. [Notice the in after 'years'.]
  • The PC 'in which' the virus was discovered has been transferred to the stock room.
  • The PC that the virus was discovered in has been transferred to the stock room. [Notice the "in" after 'discovered'.]
  • The subject 'in which' I got the highest score is Math.
  • The subject that I got the highest score in is Math. [Notice the "in" after 'score'.]

Well, that's the compromise. You will have to use and place in in appropriate part of the sentence if you opt to use where and that instead of 'in which'.


Why is it that we have adapted to using the word 'which' outside of interrogative sentences?

The relative pronoun 'which' is not only for interrogative sentences. It is also used in statements as in the following ways:

  • I shopped at the store which sells trendy dresses and shoes.
  • The owner of the car which hit our van did not appear during the mediation.

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