They don´t take ` –s/ -es´ in the third person.
She cans play the piano beautifully.
They are followed by an infinitive without `to’ .
She should to eat more vegetables.
They function like auxiliaries in Negative and interrogative sentences.
Can you speak louder, please? Do you can speak louder, please?
You shouldn´t talk like that. You don´t should talk like that.
They have no –ing, infinitive nor past participle forms.
canned canning to can
They provide additional and specific meaning to the main verb of the
You mustn´t drink that water, it´s dangerous.
They don´t have all tenses. They use other verbs to do that
Can → Be able to
Must → Have to
To ask for permisssion: Can I leave earlier? Yes, you can.
To express present ability: She can play the guitar
To make a request: Can I borrow your pen?
To offer to do
Can I help you?
To express possibility or impossibility:Learning a language can be a real challenge
It can´t cost more than a dollar or two.
To express past ability: Nancy could ski
like a pro by the age of 11.
To express
Extreme rain could cause the river to flood the city.
To make suggestions: You could see a movie or go out to dinner
To make a request: Could I use your computer to email my boss?
In conditional
We could go on the trip if I didn´t have to work.
To express Obligation:
You must obey the rules.
To express necessity:
Students must pass an entrance examination to study at this school.
To express certainty: This must be the right address!.
Have to
To express Obligation: He has had to leave early.
To express necessity: The soup has to be stirred continuously to prevent
To express certainty: This answer has to be right.
To express prohibition: We mustn’t talk about it. It's confidential (We have a
strong obligation NOT to talk about it)
Don’t have to
To express that something is not necessary:
We don't have to get there on time.
The boss is away today.
You don't have to come if you don't want to.
(There is no need)
To Advise: You should focus more on your family and less on work.
When you go to Berlin,you should visit the
palaces in Potsdam.
To express expectation: By now, they should already be in
To express Obligation: I really should be in the office by 7:00
Should and ought to are very similar, and can often replace each
other.They are both to talk about obligation and duty, to give
advice, and to say what we think it is right for people to do.
You ought to focus more on your family and less on work
Should is much more frequent than ought to.
Request / Demand / Order (less polite than would)
Will you please close the door?
Prediction / Assumption: I think it will rain on Saturday.
Promise: I will stop smoking.
Spontaneous Decision: Can someone give me a ride? I will
To offer: Would you like some
To invite: Would you like to go to the cinema?
To express repetition in the past: When I was a kid, I would always go to the beach.
To express Possibility: It may rain tomorrow
To make a request (formal):
May I open the window, please?
Give permission: Johnny, you may leave the table when you have finished your
To express possibility:
Your purse might be in the living
To make a request ( very formal):
Might I borrow your pen?
To make suggestions:
You might visit the botanical gardens during your visit.
Need is not a modal, but it is used in affirmative sentences, like
have to, to express obligation and necessity.
I need to cook dinner tonight.
Needn’t, on the contrary, is a modal and indicates lack of obligation .
The past form of needn't for lack of obligation is needn't have:
You needn't go to the meeting.
We needn't have mentioned it - they already knew.
I can go
I must go
I can’t go
You mustn’t go
Can I go?
(Must I go?)/Do I have to go?
I should go
You shouldn’t go
Should I go?
I ought to go
You ought not to go
(Ought I to go?)/
Do you think I ought to go?

Diapositiva 1