MODAL VERBS

Modal verbs are used to express different meanings: obligation, requests, prohibition, necessity, ability, certainty or probability

• They are always followed by the BARE INFINITIVE (infinitive without TO)

           She should study harder

• They don't take the 3rd person singular -s

            She can a motorbike

• They don't use auxiliaries (do,does, did..) to form negatives or questions

          He mustn't run at school
          Can you open the window, please? 

1.- ABILITY AND REQUESTS

• ABILITY

CAN (present) /COULD (past /BE ABLE TO (other tenses)

I can play the guitar (general abilty)

I could play the guitar (general ability in the past)

I will be able to meet you tomorrow

MANAGED TO- also used when there's something difficult or an obstacle to overcome

I did my driving test yesterday and I managed to pass it

• REQUESTS

CAN/COULD (A BIT MORE FORMAL)

Can you lend me a pen, please?

Could I speak with you, please?

2.- OBLIGATION, PROHIBITION OR ADVICE

OBLIGATION

MUST/HAVE TO/HAD TO (past)

I have to help my mum this evening

He must study harder if he wants to pass the test

I had to work very hard when I was young

NEED 

I need to improve my marks if I want to go on holiday with my family

CAN'T

You can't smoke here. It's not allowed

ABSENCE OF OBLIGATION

DON'T HAVE TO/ DIDN'T HAVE TO/  DON'T NEED TO/ DIDN'T NEED TO

He doesn't need to wear a uniform to school (it's not an obligation)

He doesn't have to wake up early tomorrow. It's Saturday (not an obligation)

3.- ADVICE

SHOULD/OUGHT TO

I think you should do more exercise

You ought to eat more healthily

4.- PROBABILITY AND CERTAINTY

PROBABILITY

MAY/MIGHT/COULD

It's cold and cloudy. It may rain

You might get a cold if you don't wear a coat

CERTAINTY

MUST 

The lights are on so he must be home

IMPOSSIBILITY

CAN'T

He can't be working today. He went on holiday yesterday!

MODAL PERFECTS

modal+have+past participle

They are used to express certainty, probability o to express something could have been different in the past:

He might have phoned her last night 

He must have felt disappointed when he failed the test (certainty)

It can't have been Rachel! She was in London (impossibility)

We should have gone cycling (but I didn't and I regret it)

GET SOME PRACTICE HERE