Interrogative clause or relative clause?

Question

A student (high school age) asked me if "that you are least proud of" in What have you done that you are least proud of? is an interrogative clause or a relative clause. My answer was based on intuition rather than solid linguistic background.

My answer: it depends. If the clause is asking about something that the speaker doesn't know about, it's interrogative. If the clause is actually factual, it's a relative clause. In other words, the speaker already knows what the answer is and simply wants the other person to acknowledge this answer in the conversation (that is, the speaker is not seeking the answer to what he doesn't know).

Is my intuition correct, or is there a better way of analyzing such sentences?

Thanks

Answer 1

I don't see how "that you are least proud of" could be an interrogative clause. It starts with the relativizer that, which as far as I know is not used with interrogatives.

The sentence as a whole is interrogative, but that's because of the word what in the matrix clause.

Answer 2

Not quite, Puzzled. I can ask a question even though I know the answer. I might, for example, be testing you or interrogating you.

The question you are asking about begins with the interrogative pronoun, ‘what’. The main clause is interrogative.

“What have you done?” on its own, however, is not much of a question. So the ‘what’ is explained in a subordinate clause, introduced by the relative pronoun, “that”. So the subordinate clause is a relative clause.

When I was at school, and till comparatively recently, speakers of British English would have used the relative pronoun ‘which’ and would not have left the preposition to the end. Instead

What have you done of which you are least proud?

would have been more correct. The use of the demonstrative adjective as a relative was seen as an American usage. But this usage is becoming current British usage also.

Answer 3

 "You have done something that you are least proud of"  

object of "done" is questioned:

 "You have done what that you are least proud of?"

wh-expression is fronted with subject-aux inversion of "have":

  "What that you are least proud of have you done?"

relative clause is extraposed:

  "What have you done that you are least proud of?

Answer 4

Here's our comparison.

If it's interrogative, there asking 4 ways to what will happen, such as which, who, what, etc.

If it's relative clause, modifying a adjectives, noun and pronoun are these 5 words like: that, which, who, whom, whose and those words ends with -s only for which and that.

These relative clause including "that" and "which" both of them is subject to giving more information about the subject. While "who" is person to give more information about a person

here's an example of the question

Interrogative

Who's the other guys here?

Relative clause

The one guy who had the other guys