When my Russian students read a task or instruction or when I give instructions to them they often don't understand them immediately and ask questions like
'Should I do this exercise?', or
'Should I ...
I was taught that there is a difference in the kind of obligation one can express through 'must' and 'have to'. If I say
I must do this.
I imply that I feel an inner urge to do this, whereas if I say
I've heard a sentence like this:
"I had to go to the doctor" for an obligation in the past.
I would have expected:
"I hadn't to go to the doctor" for the negative form, but I heard:
"I haven't had to ...
Can "You mustn't have done that" have a similar meaning to "You shouldn't have done that" / "You were not supposed to do it (but you did)"?
(not logical probability but obligation)
Since we have the ...