Point #1 Must shows necessity. We usually use must when someone makes a rule or law that we need to follow. The necessity usually comes from the rule or law or the person/authority who made the rule/law.
When you must do something, there is no choice:- When you travel abroad, you must have a passport. Having a passport is a law
- You must stop at a red light.
- You must speak quietly in the library.
Point #2
Must can also be used when the speaker feels the situation is urgent. In this case the necessity comes from the speaker’s belief that the situation is urgent.
- I must talk to the doctor right now. It is urgent.
- There is an emergency. I must use your phone.
Point #3
The negative form of must is must not. However, the meaning is prohibition (in other words, don’t do that
- You must not smoke here. This means, “Do not smoke here.”
- You must not pass a red light without stopping.
- You must not speak in the library.
Point #4
Have to is like must. Have to shows necessity and we use have to when someone makes a rule or law that we need to follow. The necessity usually comes from the rule or law or the person/authority who made the rule/law.
- When you travel abroad, you have to have a passport.
- You have to stop at a red light.
Point #5
Have to can also be used when the speaker feels the situation is important, but not urgent. In this case the necessity comes from the speaker’s belief that the situation is important.
- I have to call the doctor right now. It is important
- I have to find out what is wrong with my car. I am taking a road trip next week.
Point #6
Have got to is the same as have to, but us usually used in spoken English. The pronunciation is godda. We usually use the contracted form, for example: I’ve godda go (or) He’s godda go, etc. When using I, we often just say, I godda
- I godda talk to the doctor tomorrow (or) I’ve godda talk to the doctor tomorrow.
- When you travel abroad, you godda have a passport.
- You godda stop at a red light.
Point #7
Had to is used to talk about past necessity. There is no past form of must to mean necessity
- When I traveled abroad, I had to have a passport.
- You had to stop at the red light. That’s why the police stopped you.
- I had to talk to the doctor yesterday. It was urgent.
Point #8
In a negative sentence don’t have to is used to talk about what is not necessary.
We do not use don’t must
- When you travel from New York to Miami, you don’t have to bring a passport.
- You don’t have to stop at a green light.
- I don’t have to talk to the doctor now. I am feeling better.