Must - Have to:
Must and have to both express obligation.
However, they are used differently depending on who imposes the obligation.
MUST:
The speaker thinks it is necessary.
• I must buy flowers for my mother
(It's her birthday and I decide to do that).
• "You must take more exercise"
says the doctor.
(The doctor thinks it is necessary).
• I must ask my secretary to book a flight for me.
(It is important for me not to forget.)
• "Dogs must be kept on a lead"
(Written on a sign in the park =
a rule which must be respected)
HAVE TO:
Someone else thinks it is necessary.
• I have to buy flowers for my mother-in-law.
(It is not my decision -
my husband asked me to do it.)
• I have to take more exercise.
(doctor's orders!)
• I have to call the travel agency.
(My boss asked me to book a flight.)
• I have to keep my dog on a lead.
(That's what the sign tells me to do.)
N.B. In the negative form, the meaning changes!
MUST NOT (MUSTN'T)
You mustn't tell George
= it's important not to tell George
= don't tell George
DO NOT HAVE TO (DON'T HAVE TO)
You don't have to tell George = you can tell George if you like,
but it isn't necessary. It's your decision.
Subject: Must - Have to 
Mon Aug 11, 2014 2:31 pm
