Modal verbs: Have to, Must

this guy was singing in 1965..


"..And nobody has ever taught you how to live on the street
And now you find out you're gonna have to get used to it..."
 



Have to do something means that it is necessary to do it: is used to express a strong obligation. 
examples: 
- I have to arrive at work before 8 o'clock tomorrow morning, I have a client at 8,30.
- You have to pass your last five exams get the bachelor degree.
- I have to send a my report by the end of the week.

- Matteo doesn't have to work on Saturdays. (negative form)

- Why did you have to go so early yesterday evening? (questions)

- I don't know if I can come to the seaside next weekend, I might have to work. (have to with might)

the same man has been telling us about another story saying:

"..How many roads must a man walk down,
before you call him a man?
How many seas must a white dove sail,
before she sleeps in the sand?
yes and how many times must a cannon ball fly.."

  

[...This lyrics excite abstract statements rather than particular and specific examples. They excite both the imagination and emotions, it enables you to unlock your own highly personal box of images, memories, connections and associations. Keep them in your mind as they are beautiful songs...] 

Must is similar to have to:
- You must come and see us again soon.
- You have to come and see us again soon. (is also possible)

• Must can be used to give your personal opinion, to say what you think is necessary or to recommend somebody to do something. But have to is also possible: - They must do something about it.  - I must say, I don't think you were very nice to her. 

• Must to show that we are certain something is true. Actually, we are making a logical deduction based upon some clear evidence or reason: - You must be worried that she didn't call you yet. - It must be nice to live in Marbella in summer. 

• Must is often used in written rules and instructions: - Application forms for the job must received by October the 10th. - In this exam, pencils are not allowed, you must write your answers in ink.

NOTE:

Have to to express a strong obligation. 

When we use have to this usually means that the speaker is not giving his personal opinion, but rather some external circumstance makes the obligation necessary:

- I have to work from 9 to 6 o'clock, every day. (this is a fact, not an opinion)

- I have to pass my last exam or the university won't accept me.

ALSO

Especially, in British English, have got to is used to mean the same as have to.

- Ciccio is a bartender. He's got to work mainly at weekends.

- Have I got to do it right now?

 

BUT

Mustn't and don't have to are completely different:

 

You mustn't do something = it is necessary that you do not do it:

- You must keep the secret! You mustn't tell anyone

- You mustn't phone me at work. We aren't allowed to receive any personal calls. 

You don't have to do something = you don't need to do it, but you can if you want:
- You don't have to tell them, but you can if want to.
- I don't have to go to lesson today, but I'll think I'll go anyway.