This question already has an answer here:
A BBC reporter, Melissa Hogenboom, talks about her father in this BBC article "The part of my dad that dementia can't take":
My dad does not fall into any of the risk categories for dementia. There is no family history of it. He’s always been slim, healthy and active. This is part of why the disease is so devastating – it can affect anyone and we still do not understand why.
Is this 'why' a fused relative word or an interrogative word?
This question does NOT have an answer in the earlier question fused relatives versus interrogatives.
There, the answer by John Lawler cites, and is solely based on, Haj Ross's paper "Conjunctive and Disjunctive Wh-clauses."
The paper, however, is irrelevant in that both conjunctive and disjunctive wh-clauses are interrogative clauses.
In fact, more than a month ago, I posted a comment to John Lawler's answer and asked about his opinion on the alleged misquoting of the paper and the writing up of an answer based on the misquoted paper. But unfortunately, I have not heard from him ever since.
So, whoever cited John Lawler's answer there as an answer to my question should go to that earlier question/answer and "read" the answer, the paper, and my comment there, although I think they should have done all that before marking this question as a "duplicate," whatever that means.