1. I don't know [who's responsible].
  2. I don't know [who's the best person for this job].
  3. I don't know [what's best].

I'm assuming sentences 1–3 are grammatical. How are the parts in brackets analyzed? I know in relative clauses subject–auxiliary inversion doesn't occur, unlike here, so these aren't relative clauses, are they? Are these "fused relatives" or "content clauses" or what? What would a modern analysis be? (I'm not asking for anything detailed here, just the general structure and the relevant terminology, essentially.)

Related to the above:

  1. I don't know who responsible is.
  2. I don't know who the best person for this job is.
  3. I don't know what best is.

Sentence 4 sounds weird/wrong, 5 sounds okay(?), and 6 sounds okay if you're asking about the word "best", I suppose. How come it's sometimes possible to transform the original sentences like this?

  • I don't know [which person] is responsible. I don't know [which person] is the best for this job. I don't know [what thing] is best, or [what action] would be the best one. Commented Jun 13, 2021 at 16:29
  • Indirect questions, and the fact that they generally follow the pattern 'I don't know what the answer to the question "Who is best?" is' → 'I don't know who is best' have been addressed many times. 1-3 are standard, as 405 says. 4 and 6 are incorrect; they should follow the usual pattern. 5' 'I don't know who's the best person for this job' would again be standard, but 5 requires that the verb come after the lengthy NP (the best person for this job). cf 3' ('I don't know what the best thing to do [given the fact that the Covid restrictions seem likely to stay with us for weeks yet] is.' Commented Jun 13, 2021 at 18:48

2 Answers 2


In all cases, the elements in brackets are noun clauses, acting as the object of the verb "know". A simpler example would be, "I don't know [something]. The clauses in all three of your examples could be the "something", so they are noun clauses.

Example 2 is not grammatical because you've done sub-aux inversion. "I don't know who the best person for this job is" is correct, and it happens to be your 5th example.

Example 4 is nonsense.

You're right that example 6 could mean you don't know what the word "best" means, and could also mean, "I am incapable of assessing what 'best' would be in this situation", perhaps because you're unqualified, or because 'best' hasn't been adequately defined.

  • They are definitely clause, but not noun clause. This term is very irritating and that doesn't mean anything to me. Though you might argue that over the internet that term is used so many times. So does fake news and wrong info. Example 2 which you marked as ungrammatical is actually grammatical and correct, and in use. As for example 6, it is not prudent to analyse the meaning of a wrong sentence. Commented Jul 24, 2021 at 6:36
  • Great answer. In the sixth example, I would probably disambiguate by putting the word “best” in quotation marks.
    – Davislor
    Commented Nov 20, 2021 at 12:54

A relative clause is a finite clause that modifies a noun and is a constituent of the noun phrase which has the noun as its head (for example, the umbrella that I borrowed).

Relative clauses can begin with a relative pronoun (such as which, that or who), a preposition and a relative pronoun (for example, to whom, for which) or no subordinator (for example, the umbrella I borrowed).

To identify a relative clause without a subordinator, we can insert a relative pronoun to see if the sentence still makes sense, for example, the umbrella (that) I borrowed.

Ref Grammarpedia

  1. I don't know [what's best].

This is ambiguous because of how "best" can be used. I suggest this should be either

I don't know [what's the best]

the best one or sort

I don't know [what's for the best]

the best decision.

I would suggest that point 4 through 6 all sound incorrect. Therefore the next three points I will correct

I don't know who the responsible person is.

Only animals or Humans can be responsible, we must use who or that. Also we are being specific so we use the definite article.

I don't know who the best person would be for this job

I don't know what would be the best

I don't know what would be for the best

using "would" introduces a possibility "what's the best alternative"

is; he/she/it form of be Ref C.E.D.

  • 1
    These are noun clauses, not relative clauses as they form the object of "know", and do not modify any noun
    – gotube
    Commented Jun 14, 2021 at 22:49

You must log in to answer this question.