Expressing necessity: Must, Have to, Have got to

Examples:

(a) All applicants must take an entrance exam.
(b) All applicants have to take an entrance exam.

Must and have to both express necessity.
In (a) and (b): It is necessary for every applicant to take an entrance exam. There is no other choice. The exam is required.

(c) I'm looking for Farzana. I have to talk to her about our lunch date tomorrow. I can't meet her for lunch because I have to go to a business meeting at 1:00.
(d) Where's Farzana? I must talk to her right away. I have an urgent message for her.

In everyday statements of necessity, have to is used more commonly than must. Must is usually stronger than have to and can indicate urgency or stress importance.

In (c): The speaker is simply saying, "I need to do this and I need to do that."
In (d): The speaker is strongly saying, "This is very important!"

(e) I have to ("hafta") be home by eight.
(f) He has to ("hasta:) go to a meeting tonight.

Note: have to is usually pronounced "hafta"; has to is usually pronounced "hasta".

(g) I have got to go now. I have a class in ten minutes.
(h) I have to go now. I have a class in ten minutes.

Have got to also expresses the idea of necessity:
(g) and (h) have the same meaning. Have got to is informal and is used primarily in spoken English. Have to is used in both formal and informl English.

(i) I have got to go ("I've gotta go/I gotta go") now.

Usual pronunciation of got to is "gotta". Sometimes have is dropped in speech: "I gotta do it."

(j) Present or Future: I have to/have got to/must study tonight.
(k) Past: I had to study last night.

The idea of past necessity is expressed by had to. There is no other past form for must (when it means necessity) or have got to.


Cheers!
Naeem