Modal Verbs

Modal auxiliary verbs in the English language are:
can, could, may, might, must, shall, should, will, would.
Some words and phrases related to modal verbs also deserve attention. Such examples are: be able to, have to.

Unlike other verbs, modals
1) do not change form
You do not add –ed for past tense or –s in the present. The future is not formed with 'will', and 'can' in the future is not “will can”, but „will be able to”.
2) to make a negative, we simply add „not”
can - can not
should - should not
must - must not
might - might not
3) to ask a question, we place them at the beginning of the sentence
Can you swim?
Should I leave?
Could you help me?
4) unless in short answers, there is another verb "glued"to them and they cannot be used without one
He might arrive late.
They would do that any time.
You must carry your passport at all times.
5) the verb that follows them can be in one of three forms: do, be doing, have done. 
- When using "be doing", we are talking about a current activity:
This can't be happening to me!
You should be writing your homework right now, not eating doughnuts!
He must be watching television, I can hear voices.
- We use "have done" when the action is from the past, as in:
It might have been my brother, I don't know.
You should have done it when you had the chance.
I would have agreed.

Exercises