Learn the differences between Must vs. Have to, and Mustn’t vs. Don’t/Doesn’t Have to…
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Must vs. Have to
– Express personal obligation
– Express what the speaker thinks is necessary
– Express subjective obligation
I must go to bed earlier.
You must answer all the questions.
– Express impersonal obligation
– The subject is obliged or forced to act by a separate, external power (for example, the Law or school rules)
– Express objective obligation
I have to arrive at work at 9 sharp. My boss is very strict.
In Britain, you have to drive on the left.
Mustn’t vs. Don’t/Doesn’t Have to
It is prohibited; it is not allowed. It is important that you do NOT do something. The prohibition can be subjective (the speaker’s opinion) or objective.
In the army, you mustn’t go out after 9.
You mustn’t drink wine.
Don’t/Doesn’t Have to
There is no obligation; you are not required to do something, especially if you don’t want to.
You don’t have to drive. I can do it.
He doesn’t have to turn here. He can turn at the next intersection.