1. You must be honest.

2. You have to be honest.
(Situation: The person is not honest, so the boss is scolding the man.)

3. You must be honest.
4. You have to be honest.
5. I am sure that you are honest.
(The man was honest, and the boss knows it, so he said this way.)
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Q 1: Can we use 'have to' instead of 'must' in the sentences above?

Q 2: They have different meaning though they have the same sentences? Right?
Would you help me with this matter?

2 answers

Q. 1 Yes

Q. 2 All of the sentences mean the same.
In each case, the pronunciation of the words in each sentence will convey the meaning. Here's how:

1. You must be honest.
2. You have to be honest.
(Situation: The person is not honest, so the boss is scolding the man.)
[Pronounce the words in bold more loudly than the other words in each sentence.]

3. You must be honest.
4. You are obviously honest.
5. I am sure that you are honest.
(The man was honest, and the boss knows it, so he said this way.)
[Pronounce the words in bold more loudly than the other words in each sentence.]

Let us know if this doesn't make sense, but sometimes pronunciation is the only way to tell the differences in meanings.