Modals belong to a large category of auxiliary or helping verbs which are used to modify the meaning of  the main verbs with which they are used. They cannot be used on their own.

Modal auxiliaries help to express:

i)Ability      ii) Possibility     iii) Permission     iv) Command     v) Obligation

vi) Certainty  vii) Futurity     viii) Request    ix) Suggestion   x) Necessity

 Certain features of modal verbs separate them from primary auxiliaries.

Can, could, may, might, shall, should, will and would are called pure modals because:

• They are not used on their own and is always used with a main verb. ( in  its bare infinitive form.)

Can you dance? Yes, I can. (Yes, I can dance.)

• They do not change in third person. She will come. (not – She wills

Come)

• Need and dare are both used as main verbs and as modals.

I need some rest. (main verb)

You need not come here again. (modal)

(As a modal need is mostly used with not)

She dares to take up the challenge. (main verb)

He dare not speak against his boss. (modal)

Uses of Modal auxiliaries

CAN

1. To ask for permission – Can I close the window?
2. To express possibility – We can do the project in a day, if we work all night.
3. To express ability – She can run very fast.

COULD

1. To express ability in the past. – He could swim across the river in his youth.
2. To express polite informal requests – Could you pass on the salt please?
3. To express possibility under certain conditions. – If you had studied well, you could have passed.

_MAY

1. To ask for permission (informal ) – May I come in?
2. To express possibility – His uncle may visit them soon.
3. To make a request – May I help you with the luggage?
4. To express faith, hope, wish – May all your dreams come true.
5. To express purpose – Push me up so that I may climb the wall.

MIGHT

1. To express possibility – It might rain today.
2. To express doubt – You might be late for the programme.
3. To express speculation – He might contest for the election.
4. To express purpose – You might read this book to increase your knowledge.

SHOULD

1. To express duty- You should respect elders.
2. To express advice – You should work hard.
3. To express obligation – We should care for the environment.
4. To express probability – They should have reached the airport by now.

WILL

1. To express possibility – If you don’t study hard, you will fail.
2. To express insistence – I will succeed or die in the attempt.
3. To make a request – Will you have some tea?
4. To express volition – I will carry your suitcase.

WOULD

1. To express past habits – I would visit the church often in those days.
2. To express an imaginary condition – I would buy Eiffel tower, if I had the money.
3. To express wish – If I would only learn to fly.
4. To express possibility – I would go there, if I were allowed.
5. To express polite request – Would you step forward please?
6. To make a promise – He would never go there again.

MUST

1. To express compulsion – You must obey orders.
2. To express determination – I must get a good grade.
3. To express certainty – Man must die one day.
4. To express possibility – She must be extremely rich.
5. To express emphatic advice – You must tell only the truth.

OUGHT TO

1. To express moral obligation – One ought to respect his nation.
2. To express past obligation – You ought to have helped her.
3. To express strong possibility – Pete ought to win this match.
4. To give advice – You ought to have outdoor activities more often.

USED TO

1. To express past habit – He used to live in a village.
2. To express existence of things in the past – The used to be a garden here.

NEED

1. To express necessity – You need to brush up your speaking skills.
2. To express futurity – Need I come tomorrow?
3. For forming negative sentences – You need not come again.

Categories of modal verbs

Modals can be divided into three categories

1. DETONIC MODALS

These modals give directives by giving permission or telling about obligation – e.g. 

You may come in.

She must finish writing her novel.

• DYNAMIC MODALS

These modals express ability and volition

Sudha can sing bhajans.

I will go where I want.

• EPISTEMIC MODALS

These modals express possibility and necessity

He may be in his office.

It might rain.