Modal auxiliaries and similar expressions

Summary: modal auxiliaries and similar expressions
Auxiliary	Meaning	Example
Can	Ability	I can sing.
	Polite question	Can you please help me?
Could	Past ability	I couldn’t go to class yesterday.
	Polite question	Could you please help me?
May	Possibility	It may rain tomorrow.
	Polite question	May I help you?
Might	Possibility	It might rain tomorrow.
Must	Necessity	You must have a passport.
Should	Advisability	You should see a doctor.
Will	Future happening	I will meet you ath the airport.
Would	Polite question	Would you please open the door?
Be able to	Ability	I wasn’t able to attend the course.
Be going to	Future happening	I’m going to meet you at the airport.
Have to	Necessity	I have to study tonight.
Had to	Past necessity	I had to study last night too.