What is the difference between "in which" and plain "which"? Can they be used interchangeably? For instance what is the difference between these two sentences:

The party in which I attended was fun.


The party which I attended was fun.
  • Do you have examples? As your question stands, it’s not clear where your confusion may lie. – Robusto Jan 19 '19 at 22:36
  • 2
    The use of "in" is because there is a preposition phrase that requires it. Not because it is tied to which in some way. – Jim Jan 20 '19 at 1:26
  • Try this as an example "Go down the corridor and find the door which has my name on it. In that room is my desk on which is a folder, in which is the agenda for this meeting." Does that help? – BoldBen Jan 20 '19 at 14:52

A classic example of in which not being replaceable with which may be seen in the film In Which We Serve.

Of course, to be strictly correct, it is the title of the film in which the example can be seen, not the film itself.

More broadly, if Thing 1 can be verb + in Thing 2, then Thing 2 is the thing in which Thing 1 is verbed.

Paddington Bear got lost in the Early Stamp Section of the Royal Postal Museum. The Early Stamp Section was subsequently much remarked upon for being the section of the museum in which Paddington Bear got lost.

There are many ways to phrase a thought. However, in which and similar expressions make it possible for the writer to put their main idea at the place in the sentence that gives it the greatest impact - the point at which the speaker’s emphasis most naturally falls.


As a general answer, I don't feel like they can be used completely interchangeably, but there may be sentences where they can be swapped with little to no semantic change and still remain grammatically correct.

M. C. asked a question in which the difference between 'in which' and plain 'which' was raised.


M. C. asked a question which raised the difference between 'in which' and plain 'which'.

Both of these sentences are valid and mean the same thing. But the sentence had to adjust to accommodate dropping the 'in'. If I knew your pronouns, the first version could be modified to a more active tense for the prepositional phrase which would require a more substantial change to drop the 'in'.

I do feel more examples could help qualify exactly how to describe the difference.

See also How to correctly apply "in which", "of which", "at which", "to which", etc?, in which the matter is further discussed, though I don't feel it makes this a duplicate because that was closed as being off topic, possibly for being too broad.

  • Both of those examples, but especially the first one, seem awkward to me. The phrasing I would use is "...a question about the difference between...". – Laurel Jan 20 '19 at 0:58
  • This is really an awesome and thorough answer. I was going to pipe in, but you really said it right to the point. Thanks! – Jesse Steele Jan 20 '19 at 2:23
  • @Laurel I think the word 'contrived' fits a bit more than awkward. At least, to me, contrived has awkward implicit within it, but also explains a bit why it's awkward. I would have also used that same phrasing, but for the fact that I was going for an example in which either 'in which' or 'which' could be applied... and there I might have my example of a case where 'in which' works but 'which' doesn't without a whole bunch of rewording. – Ed Grimm Jan 20 '19 at 4:49

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