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.
		Past simple			They had to wait.