Modal verbs

Modal verbs are a particular kind of auxiliary.

Look, I can do it! – Oh yes! So you can.
Can I use your phone? – Of course you can.
Do you think she will come? – I’m sure she will.
I must get our tickets today.

Modal verbs are used when you need to add special elements of meaning to a main verb, e.g.:

to express different degrees of doubt and possibility about the action of the main verb.

I may not be able to do it.
I think that I might have caught your cold.
I could ask for you, if you like.
You couldn’t do it, could you?

to express degrees of future possibility, ranging from the definite future, will, to the possible future, may, and the conditional future, could.

You will be seeing her on Friday at Jackie’s house.
I may be late home tomorrow evening.
I could bring some more bread home with me tonight.

to request or give permission for an action to take place.

May I come in?
You can borrow my car tonight if you like.

to make a prohibition, when used with a negative.

You shouldn’t use this computer without permission.
You cannot borrow my car tonight.
He must not see this letter.

to speculate.

The weather’s so bad the flight could be late.
It might be all over by the time we get there.
He may be very cross about all this.

to express obligation and duty.

I must give in my essay today.
Helen ought to tell the truth.

to refer to typical behaviour.

She can be very kind on occasions like this.

to add politeness to a request which might otherwise sound abrupt.

Would you please close the door.

to make conditional sentences (see Conditional clauses).

in reported speech (see Reported speech).

Modals can refer to a time range that reaches from the immediate present to some future time, so that they can all be used for future reference, especially when they are used with a time adverbial. See Future reference.

You will be seeing her on Friday at Jackie’s house.
I may be late home tomorrow evening.
I could bring some more bread home with me tonight.

Some modals can refer to a time range that goes back from the immediate present to some indefinite past time. They can refer to habitual action when they are used with a time adverbial.

When I was little, I would ride my bike round and round the lawn.

Form

Unlike other verbs, modal verbs have only one form, the base form, and only one tense, the present simple.

You will be seeing her on Friday at Jackie’s house.
I may be late home tomorrow evening.
I might go to visit Grandma on Saturday.

They do not have a to infinitive. They have no -s inflection in the 3rd person singular.

He will be seeing her on Friday.
She may be late home.

Since modal verbs do not have past tense forms, you have to use other verbs to provide some of the modal meanings in the past, e.g. past necessity is expressed by had to instead of must.

I must visit Auntie May today.
I had to visit Auntie May yesterday.

The modals shall and will are usually contracted to ’ll in spoken English. All the negative forms can be contracted to form a single word such as can’t, won’t, wouldn’t. These contracted forms are common in both spoken and written English.

I will/shall = I’ll
We will/shall = we’ll
You mustn’t say things like that, Jane.
John can’t come to my party.

There are other contracted forms such as he’ll, we’ll, shan’t, and they’ll, which are common in spoken English but rare in written English.

Several verbs act as modals sometimes and as full main verbs at other times. These are called semi-modal verbs.

How dare he!
He dared to ask me to do his washing!
She needn’t come if that’s how she feels.
Monica needs a new raincoat.

Position

Modals come before any other auxiliary verb or main verb in the verb phrase.

Modal verbs are followed by the base form of the verb if there is no other auxiliary verb present.

Yes, you can borrow those earrings tonight.
You should try that new restaurant in town.
You must come over again some time.

If one of the auxiliary verbs have or be follows the modal verb, the main verb will take the appropriate present or past participle form.

I may have upset him.
You could have looked for it yourself.
Janice might be coming too.
Sue will have been worried about her, I imagine.

In negative sentences, not comes immediately after the modal verb and in front of all the other verbs.

They may not wait for you if you’re late.
He must not be disturbed after 9 o’clock.

Can cannot be combined with the auxiliary form have, but the negative form can’t can be combined with have.

They can’t have seen him.

but not They can have seen him.