Ability - Способность
can - could - be able
		Active Voice	Pasive Voice
Present	Simple	I can work	I am able to work
	Continuous
	Perfect	I have been able to work
	Perfect Continuous
Past	Simple	I could work	I was able to work
	Continuous
	Perfect	I could have worked
	Perfect Continuous
Future	Simple	I will be able to work
	Continuous
	Perfect
	Perfect Continuous
Future in the past	Simple
	Continuous
	Perfect
	Perfect Continuous
Obligation - Обязанность
must - have to - should - ought to
		have to	must	should	ought to	need
Present	Simple	I have to work	I must work	I should work	I ought to work	I need to work
	Continuous
	Perfect	I have had to work
	Perfect Continuous
Past	Simple	I had to work
	Continuous
	Perfect	I had had to work
	Perfect Continuous
Future	Simple	I will have to work
	Continuous
	Perfect	I will have had to work
	Perfect Continuous
Future in the past	Simple	I would have to work
	Continuous
	Perfect	I would have had to work
	Perfect Continuous