Modal Verbs: Must V.S. Have to

Modal verbs  Must V.S. Have to

1.    Must is similar to have to. We can use “must” to give our own opinion (personal obligation/ for ex. To say what you think necessary, or to recommend someone to do something). Have to is also possible.

Ex: 1. I haven’t spoken to Sue for ages. I must phone her. ( = I say this is necessary.)

                                  (I have to phone her. Using have to is also OK.)

   2. Mark is a really nice person. You must meet him. (I recommend this.)

                               (You have to meet him. Using have to is also OK.)

   3. You must come and see us again soon. ( I recommend this.)

     (You have to come and see us again soon. Using have to is also OK.)

2.    We use have to (not must) to say what someone is obliged to do. The speaker is not giving his/ her own opinion (external obligation).

Ex: 1. I have to work from 9.00 to 8.00 every day. (a fact, not an opinion.)

   2. Jane has to travel a lot for her work. (a fact, not an opinion. It’s what she has to do for her work.)

3.    For written rules and instructions, we use must.

Ex: 1. (Exam instruction) You must write your answers in ink.

   2. You must not run in the classroom.

4. You cannot use must to talk about the past:

Ex: We had to leave early. (not we must)