I came across the following weird restrictive relative clause in which 'of which' is used in place of 'whose'. Actually, l am not quite sure whether it is correct or not.

The plane (the right engine of which broke down) has been repaired in Cairo Airport.

  • Makes no sense to me. Could you elaborate on why you think it might be correct?
    – Boondoggle
    May 28, 2019 at 18:37
  • Possible duplicate of Defining and Non defining Relative clauses May 28, 2019 at 18:52
  • @Edwin Ashworth: My question is not an exact copy of the one you are referring to. May 28, 2019 at 20:04
  • Are you saying that you think it's incorrect? Why? Are you suggesting that it should be "whose right engine broke down"? Why? What research have you done regarding when to use whose vs of which? May 29, 2019 at 15:31

2 Answers 2


I don't know of any reason why that sentence should be considered syntactically incorrect in formal written English. "Of which" is not a very natural start to a relative clause, but it is an acceptable one in this kind of English: it uses the relative pronoun which, which can stand for an inanimate noun phrase like "the plane", and the preposition "of". The preposition comes before the relative pronoun because of what linguists call "pied-piping". There are some restrictions on pied-piping, but I don't think this sentence violates any of them. Maybe some speakers/writer have stricter restrictions on pied-piping in this context than I do.

If you convert it to separate sentences, it makes sense and is clearly grammatical:

(The right engine of the plane broke down.) The plane has been repaired in Cairo Airport.


The phrase "of which" is usually used in non-defining or non-essential relative clauses, which are offset by commas, and which are not essential to identifying the particular antecedent.

If the context of the sentence makes it clear what particular plane is being referred to, the sentence is correct if you add the commas:

The plane, the right engine of which broke down, has been repaired in Cairo Airport.

However, if knowing that the right engine broke down is in fact essential to identifying the plane in question, the relative clause is essential, and must use a relative pronoun (which will require some rewording):

The plane whose right engine broke down has been repaired in Cairo Airport.

The plane which had a broken-down right engine has been repaired in Cairo Airport.

  • 1
    This is incorrect. Restrictive relative clauses, as well as non-restrictive ones, can have such relative expressions with "of which". "The constructions of which I speak have the intonation and interpretation of restrictive relatives."
    – Greg Lee
    May 28, 2019 at 18:59
  • That "of which" is a prepositional phrase, not a relative pronoun. That does make me second-guess the assertion in the original question, though, that the quoted phrase is a relative clause, since the pronoun is neither the subject nor the object of the verb in the clause. May 28, 2019 at 19:27
  • The word "which" is a relative pronoun. It remains a relative pronoun when it occurs in the prepositional phrase "of which".
    – herisson
    May 28, 2019 at 19:58
  • @Geekahedron: Your suggested rewording is ok, but your '... not completely correct' is ambiguous. May 28, 2019 at 20:12

Not the answer you're looking for? Browse other questions tagged or ask your own question.