Modal Verbs'

St. Mark's & St. Gabriel's                                                                                               3^rd Preparatory

' Modal Verbs'

The modal verbs are : can, could, must, will, would, shall, should, may, might, etc. They have the same form in all persons. They come before the subject in questions and take not after them in the negations. They take an infinitive without to after them.

To express ability we use:		To express possibility / probability we use :
Can (ability in the present or future) e.g. Can you swim? – No, I can't.		May ( = perhaps, very probable) e.g. He may be back before lunch.        (it's probable)
Could (ability in the past for repeated actions) e.g. He could play tennis for hours when he was        your age.		Might (=perhaps, very possible) e.g. There might be some cheese in the fridge.         (it's possible)
Couldn't (for repeated or single actions) e.g. She couldn't find her purse (single action) e.g. He couldn't drive when he was young           (repeated action)		Could (=possible) e.g. He could still be at work.        (it's possible)
N.B. Can is the Present simple form and Could             is the Past Simple.		Must (it is almost certain; I think) e.g. They look identical. They must be twins.
Degrees of certainty : 'Present Time' He is sick    →    100 % sure He must be sick    →    95 % sure He may be sick He might be sick            less than 50 % He could be sick	Can't (it doesn't seem possible; I don't think ) e.g. You have been sleeping for 12 hours.        You can't be tired . (I don't think it's possible that you are tired)
	N.B. Although might is the past form of may, yet          it can be used for present situations too.

To express obligation or necessity we use:	To express advice we use:
Must (strong obligation or necessity) e.g. We must behave ourselves in class.         (obligation)         You must take the cat to the vet.          (it's necessary)	Should / ought to e.g.  You should give up smoking!         You ought to do some exercise.         ( general advice)

To express absence of necessity or prohibition

we use:

Mustn't (prohibition)

e.g. You mustn't pick up those flowers

Can't  (prohibition)

e.g. You can't enter the club without a card.

         (you are not allowed)

Degrees of certainty: 'Past Time'

She was sick  → 100 %

She must have been sick → 95 %

She may have been sick

She might have been sick        less than 50 %

She could have been sick

P.S.   'Would' is used for repeated actions in the past.

           e.g. When I was a child, my father would read me a story at night .

                  Whenever a stranger came to our house, I would hide in the closet .