MODAL AUXILIARIES

We often refer to them as ‘modal verbs’ or ‘modals’ and use them with other verbs, for example, to ask for permission:

         May/Can I use your phone please?

There are ten modal verbs:  can, could, may might, will, would, shall, should, must and ought to;  and three ‘semi-modals´:  need, used to and have to.

Important Caraterístics

-      We use the base form of verbs after modals, not `to´:

I can see you tomorrow.  (Not *can to see*)

-      There is no – (e) s in the 3^rd person singular:

The doctor can see you now. (Not *cans*)

-      Questions/negatives are formed as for be:

Can she come with us?  She can´t come with us.

Modals have only two forms: present and past or perfect

Present: example, He must be right.

Past or perfect:  He must have been right.

USES OF MODAL VERBS

1.   Expressing present and past ability

We use can or am/is/are able to to describe natural or learned ability:

         Jane can run fast.  John can dance well.

We use could for general ability in the past:

         Jane could run fast when she was young.

We use was/were able to or managed to for the successful completion of an action

in the past:

         I was able to get/I managed to get two tickets for the play tomorrow.

           (Not *could get*)

We use can (present) or could (past) for the senses:

         Cats can see very well in the dark.

         I couldn´t hear what he said.

2.   Asking for permission

We can ask for permission in four ways:

-      with Can, which is the least formal:

Can I borrow your umbrella please?

-      with Could, which is more polite than Can:

Could I borrow your umbrella please?

-      with May, which is more `respectful’:

May I borrow your umbrella please?

-      with Might, which is very polite, but not common:

Might I borrow your umbrella please?

We can also precede such requests with I wonder if and Do you think: 

         I wonder if I could borrow your umbrella?

3.   Giving and refusing permission

We give and refuse permission with can and may:

         You can(`t)/may (not) stay out past midnight.

To be more emphatic, we use be allowed to:

You´re  allowed to/not allowed to bring food in here.

We express total prohibition with mustn´t:

         You mustn´t drive without your glasses.

4.   Past reference to permission

May and must are not `complete verbs´, so we use was/were allowed to,

not could, for past reference:

         The children were allowed to watch TV last night.

5.   Certainty and uncertainty

We can express degress of certainty on a scale to refer to the present:

         They are at home. (= it´s a certain fact)

         They should be at home. (= a probability)

         They could be at home. (= doubful possibility)

         They may be at home. (= allowing a possibility)

         They might be at home. (less certain than may)

We can express degrees of certainty in the negative on a scale to refer to the present:

         They aren´t at home. (= it´s a certain fact)

         They can´t be at home. (= it´s nearly certain)

         They couldn´t be at home. (less certain than can´t)

         They may not be at home. (allowing a possibility)

         They might not be at home. (less certain than may)

We express past degrees of certainty like this:

         They were at home.

         They could have been at home.

         They weren´t at home.

         They can´t/couldn´t have been at home.

6.   Deduction

We express deduction with must be, the negative of which is can´t be (present); and must have been, the negative of which is can´t have been (past):

         If she´s eating, she must be better.

         If she isn´t eating, she can´t be better.

         If she was eating, she must have been better.

         If she wasn´t eating, she can´t have been better.

Compare must/mustn´t to express obligation:

         You must be careful.

         You mustn´t be careless. (Not *can´t be*)

         It was dangerous, so I had to be careful. (Not *must have been*)

         It was a holiday, so I didn´t have to go to work.  (Not *can´t have been*)

7.   Offers, requests and suggestions

We use modals for the following social activities:

a)    Offering things and substances:

Would/wouldn´t you like a sandwich/some coffee?

b)   Requesting things and substances:

Can/Could/May/Might I have a sandwich/some sugar, please?

c)    Making suggestions, inviting actions:

Would/Wouldn´t you like to come with us?

d)   Requesting others to do things for you:

Will/Would you please open the door for me?

e)    Offering to do things for others:

Shall I carry that suitcase for you?

f)     Making suggestions that include the speaker:

Shall we go for a walk?

8.   Expressing wishes

We can express wishes with I wish, If only and It´s (about) time.  If only expresse more strongly the idea that the situation wished for exist, whereas wish is also uased for something that might happen.

After I wish, etc. we `go one tense back´:

-      the past tense form refers to the present:

I wish I had a better watch! (i.e. NOW)

-      the past perfect refers to the past:

If only you had asked me first. (i.e. THEN)

We may use were in all persons after I wish, etc.:

         I wish John was here now. (informal)

         I wish John were here now. (more formal)

We use could (ability), not would after I and we:

         I can´t swim.  I wish I could swim.

         We weren´t together.  I wish we could have been together!

Compare would after I wish to refer to willingness:

         I wish he would come tomorrow.

         I wish you wouldn´t make so much noise.

9.   Saying something is advisable

We use modals and other verbs to say that something is advisable.  We can do this on a scale that shows the subjective view of the speaker.

-      should (= in my opinion, it´s advisable to):

You should see a doctor.

-      ought to, which may be slightly stronger:

You ought to vote. (It´s your public duty.)

-      had better, stronger, carrying a warning:

You´d better drive more carefully next time.

-      have to/must, for inescapable obligation:

You must/You have to call home right away.

10.       Saying something is inadvisable

We use modals and other verbs to say that something is inadvisable:

-      shouldn´t (= in my opinion, it isn´t advisable to):

You shouldn´t drink so much coffee.

-      oughtn´t to, which is not very common:

You oughtn´t to park so near the corner.

-      had better not, stronger, carrying a warning:

You´d better not pass that car.

-      can´t/mustn´t for absolute prohibition:

You can´t/mustn´t turn left here.

We use don´t have/didn´t have to to mean `it isn´t/wasn´t necessary:

         I don´t have to work tomorrow.

         I didn´t have to go to work yesterday.

11.       `Used to´ for past habit

Used to is a simple past form only and refers to past habit.  If we want to say `I am in the habit of’, we must use the simple present:  I get up early. (Not *I use to get up early.*)  We use used to to make a contrast between past and present:

         I used to eat a heavy breakfast.  (but I don´t now)

         I didn´t use to get up early.  (but I do now)

                                           Source:  Essential American English (by L.G. Alexander)