The Grammaring Guide to English Grammar with Exercises

Modals to express possibility: MAY, MIGHT, CAN, COULD

Present and future

May and might + infinitive are used to express present or future possibility. May expresses a greater degree of certainty:

You should ask him. He

may/might know

Susan's telephone number.

(Perhaps he knows her number.)

I

may/might see

you later.

(Perhaps I will see you later.)

You should introduce yourself; he

may/might not remember

you.

(Perhaps she doesn't/won't remember you.)

May and might are usually not used to introduce a question. Instead, we can use Do you think? or be likely to / be likely that:

Do you think

he may/might know Susan's telephone number?

Are

you

likely to get

here before 8?

Is it likely that

you will get here before 8?

Could can be used instead of may and might with the verb be:

You

could be

right.

They

could

still

be waiting

for us.

The negative form couldn't is often used with comparative adjectives:

The food is delicious, and the staff

couldn't be

more polite.

(they are very polite)

Except for this use, couldn't expresses negative deduction, not possibility:

It's only 10 o'clock. He

couldn't be

at home.

(He is usually at work at this time of the day.)

Can may express general possibility:

Winters in Minnesota

can be

really cold.

Past

May, might and could + perfect infinitive express uncertainty with reference to past actions:

We haven't heard from him for ten years. He

may/might/could have died

.

(Perhaps he has died, but we don't know.)

But when we want to say that something was possible but did not happen, we use might or could:

He was very careless when crossing the road. He

might/could have died

.

(He didn't die.)

I

could have caught

the bus if I had hurried.

(I didn't hurry, so I didn't catch the bus.)

Couldn't + perfect infinitive is often used with comparative adjectives:

It was a great year, and I

couldn't have been

happier.

(I was very happy)

May/might not + perfect infinitive is used for uncertainty, but could not + perfect infinitive (except for the case above) expresses deduction:

I had better call Anne. She

may/might not have read

my e-mail.

(uncertainty)

It

couldn't have been

John you saw this morning. He is away on holiday.

(deduction)

Quotes:

It is never too late to be who you might have been. - George Eliot

If you don't know where you're going, you might never get there. - Yogi Berra

Related topics:

Modals to express deduction: MUST, CAN'T, COULDN'T