B- Use of have (got) to

•		The auxiliary have (got) to is used when the
	obligation comes from somewhere else.

	Example:	
	You have to be at the airport at one o'clock. 
	(The speaker remembers that this is the rule.)
	but  You must be at the airport by one o'clock. 
	(The speaker emphasizes the fact so that the
	listener doesn't forget.)
	
•		In the future and the past simple, we use have
	(got) to instead of must.

	Example: Future	I'll (will) have to be patient.
						Simple past	They had to wait.