Student or Learner
Is the following sentence correct? I doubt.
He must be a professional player, mustn't he?
It's rather difficult to construct something like that because if the "must" refers to an obligation, then we would normally expect to hear it simply as a statement, not a question.
Teacher: John's grades aren't as good as we had hoped.
Parent: That's disappointing. What can he do to improve them?
Teachers: Well, he must study harder and he really must do his homework on time.
I have constructed a rather unnatural dialogue which might happen later:
John's mother: I spoke to the teacher today. John's grades aren't very good and the teacher doesn't think he's studying hard enough.
John's father: I think I probably know what the teacher said is required. He must study harder, mustn't he?
John's mother: Yes, that's exactly what the teacher said. John must study harder.
As I said before it, that sounds very unnatural to me. The conversation is more likely to go:
John's mother: I spoke to John's teacher today. They're worried about John's grades and the teacher said he must study harder.
John's father: OK. He must study harder - is that all?
John's mother: No, he must do his homework on time as well.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
Your thanks are appreciated, but you don't need to send them in a separate post or to quote our replies back to us.
We are all happy to accept a simple click on the Like button as your acknowledgement of our help.
I think that the 'must' (= oligation) question tag is natural if 'must' implies a suggestion rather than obligation:
A: I am smoking far too much at the moment.
B: Well, you must try to cut down, mustn't you?