Grammaticality of "On which hand it is worn should not make the slightest difference"

Question

We are essentially creatures of habit. If you have any question about this, just transfer your wristwatch to the other hand. Even though it should not make the slightest difference on which hand it is worn, you will soon find that you are very aware of the change.

This is the context. Let's consider this part:

It should not make the slightest difference on which hand it is worn.

An ELL user has asked about the function of the it in this sentence, and I'd like to answer their question. As far as I know, this phenomenon is called extraposition. The clause on which hand it is worn has been moved to the end of the sentence, with the dummy it taking its place as the subject. To show how this phenomenon works, I'd like to use this sentence:

On which hand it is worn should not make the slightest difference.

I'm not a native speaker. I asked about my paraphrase on a couple of ELL websites, and everyone who answered said it was grammatical. However, here is an excerpt from The Cambridge Grammar of the English Language, Chapter 12, 6.1d:

[7]         FUSED RELATIVE                         INTEGRATED RELATIVE
i  a. What she referred to was Riga.  b. The city which she referred to was Riga.
ii a. *To what she referred was Riga. b. The city to which she referred was Riga.

When the relativised element is complement of a preposition the fused construction requires that the preposition be stranded, as in [ia]: it cannot be fronted along with its complement, as it can in the integrated relative construction [iib]. The difference in grammaticality here reflects the fact that which she referred to is a clause while what she referred to is an NP. Fronting the preposition in the integrated construction places it at the beginning of the clause, while fronting it in the fused construction places it before the NP. The deviance of [iia] is thus comparable to that of *To the city which she referred was Riga. In the integrated case the antecedent city and the relative pronoun which are distinct and the preposition can come between them, but in the fused case the antecedent and relative pronoun are not distinct and hence there is no place for a fronted preposition to occupy.

Example [iia] has the same structure as my paraphrase above — both have a preposition before a relative pronoun — yet [iia] is ungrammatical.

I asked about [iia] and got mixed answers: some said it was grammatical, some said it wasn't. I didn't ask why because I didn't expect those people to be linguists or teachers.

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• Is the clause in my example also a fused relative?
• Why is my example correct while the CGEL one is not?

Answer 1

I think that the quoted CGEL passage does not apply, because "On which hand it is worn should not make the slightest difference" does not contain a fused relative construction.

Rather than a relative construction, it seems to be an interrogative construction. ""On which hand it is worn" is not a noun phrase referring to the hand itself: instead, it means something like "The answer to the question 'On which hand is it worn?'", and as you noted in your question, it seems to internally have the structure of a clause (even though in the structure of the surrounding sentence, this clause occupies the place of the subject).

A set of similar example sentences that do involve a fused relative would I think be as follows:

1. "What it was worn on was his right hand." (= "[The thing which it was worn on] was his right hand.")
   Seems to be grammatical, even if a bit awkward.

2. *"On what it was worn was his right hand."
   Ungrammatical, according to the CGEL quote. I think I agree with that judgement.