One of my students had to fill in the gap (or leave it blank if the relative pronoun can be omitted) in this sentence:

My landlady says we can't use her sitting-room because we made too much mess the last time ________ she let us have a party.

He wrote "which". The answer key left it blank.

"Which" is not an option, while a blank or "that" or "when" are possible options. But I am having a hard time explaining to him why "when" can be omitted since grammar books seem to claim you can only leave out the relative pronouns "who/which/that".

Please correct me if you find any statements above are wrong.

And my question is: what makes it possible for "when" to be omitted? If possible, quote source for information.

  • It's apparently covered in Next Generation, Student's Book 2 by Eoin Higgins {CUP}. But you may have to buy it. Commented Oct 14, 2015 at 17:59
  • 1
    The issue is that it's a defining relative relative clause. That's what makes that acceptable and when omissible. Notice that the same thing does not apply with where - unless for some reason the antecedent is the word place. So we can have the day (when/that) we last met and the same place (that/where) we met last time but not the restaurant we met last time Commented Oct 15, 2015 at 10:14

2 Answers 2


We can generally omit relative pronouns from defining relative clauses if the wh- word does not represent the Subject. The word when replaces temporal Adjuncts, so if the clause is a defining relative clause we can nearly always remove it.

  • That was the day when you asked me to marry you.
  • That was the day you asked me to marry you.

One case where this does not seem to apply is with relative clauses using the relative word where, although for some strange reason it seems to be marginally acceptable when the antecedent is the word place:

  • That's the restaurant where we met last time.
  • *That's the restaurant we met last time. (ungrammatical)
  • That's the same place we met last time.
  • 3
    Yes, it can only occur modifying place. Why is similar, in that it must modify reason, or some word with a similar meaning (although I admit I can't think of one just now). How is completely unusable as a relative pronoun; that or Zero must be used -- the way (*how) he did it. Commented Oct 15, 2015 at 23:28

We can leave out "where, when or why"or we can use "that" instead in relative clauses. We cannot leave out " where " and "when " and use "that" in adding or connective clauses. 1.Do you remember the time when (that)we all went to a night club? 2.Can't we go next week,when I won't be so busy? From Oxford Guide to English Grammar by John Eastwood.

  • Can you please give me an example of leaving out "where"?
    – fluffy
    Commented Oct 15, 2015 at 7:53
  • Instead of a clause with "where",we can use one with a preposition.The house (that) I used to live IN has been knocked down.
    – V.V.
    Commented Oct 15, 2015 at 8:51

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