These are helping verbs which express conditions such as possibility, certainty, obligation, expectation, permission, and ability. They are also used to make polite requests and to show future time.

Basic modals

Can

Could

May

Might

Must

Shall

Should

Will

Would

Idiomatic modals

Had better

Ought to

Has/have to

Has/have got to

Be supposed*

Used to

Would rather

Be able to*

Be going to*

Be to*

Polite request

May

Might (rarely)

Will

Can (informal)

Could

Would

Should

Examples:

Shall we have coffee in the living room?

Would you please tell Mary that I called?

Permission

May

Can (informal)

Examples:

May I use the telephone?

Can I have the car tonight?

Possibility

May

Might

Should

Ought to

Must

Will

Be going to

Can

Could

Note: May, might, can, and could are "iffy"; should, ought to, and must are "probable"; will and be going to are sure things.

Examples:

It may be sunny on Thursday.

He ought to be here by four o'clock.

I will call you on Sunday.

Advisable

Should

Ought to

Had better

Examples:

You should eat more fruits and vegetables.

You had better wear your raincoat.

Necessity or obligation

Must

Have to

Have got to

Examples:

I have to go to the bank and the post office.

Taxes must be paid by April 15.

Ability

Can

Could (past)

Examples:

Can you drive a car?

Could you read by age four?

Expectation

Be supposed to

Be to

Examples:

The concert is supposed to start in five minutes.

The shuttle is to be here at 10:00 o'clock.

Prohibition

Must not

Had better not

Examples:

You must not drive without a license.

You had better not be late.

Repeated action in the past

Would

Example:

When I used to live in Montana, I would ski to work.

Preference

Would

Example:

I would rather have tea than coffee.

Future

Shall

Will

Be going to

Examples:

I will let you know tomorrow.

He is going to Portland on Friday.

Notes and comments:
Modals always work with the base or root form of the verb. Except for the idiomatic have and be expressions, modals do not change according to person, number, or tense.

Some authorities consider the verb to do in the present and past tenses (do, does, did) among the modals, but because they have other, special functions, they are not included here.