Have to , have got to & must
Use all of these to talk about what it is necessary to do
Have to : is used to say that something is necessary , and you do not have a choice about it : I'm sorry – I have to go now ./ He has to work late tonight .
Must : is used to say that something is necessary , and that you know it is a good idea : I really must study harder . / We must visit Grandma sometime soon .
Have got : is used instead of have to or must in order to emphasize how important something is : I've got to talk to him
Note : the past tense of have to , have got to , and must is had to : I had to talk to him .