Modal Verb Types

Modal verbs are similar to auxiliary verbs and are used in the positive, question and negative forms. Pure modal verbs are used in place of auxiliary verbs such as 'do', 'did' or 'have'. Here are a few examples:

Can you play volleyball?
He shouldn't go outside today.
I must leave soon to catch the train.
May I come with you?

Pure modal verbs include:

can / should / must / may 

However, there are many forms

Modal Verbs of Advice 

Modal verbs of advice are used to ask for and give advice to friends, family, colleaguesin a wide variety of situations. The most common is the simple modal verb 'should'. However, 'had better' and 'ought to' are also possible. 

should

'Should' is the most common way to give advice:

S + should / shouldn't + verb 

She should see a doctor.
They shouldn't go to school today.
We should take a vacation soon.

(?) + should + S + verb

What should I wear tonight?
When should we have the party?
Should I go to college next year?

had better

'Had better' is also used to give advice, but is more

formal.

S + had better / hadn't better + verb 

Peter had better hurry up if he doesn't want to be late.
They had better finish the work soon.
She had better write him a letter explaining the situation.

(?) + had + S + better + verb

When had she better leave for work?
What had she better do today?
Had I better finish this work?

ought to

'Ought to' is used to give advice, but is also more formal. The question form is rarely used.

S + ought to / ought not to + verb 

Tom ought to look into the situation.
They ought not to be so late for school.
Angela ought to find some new friends.

'Ought to' is generally not used in the question form.

Modal Verbs of Ability

Modal verbs of ability express someone or something is able to do. These forms are used to express facts or possibilities in daily situations. 

can

'Can' is used to speak about abilities, both on a daily basis and in specific situations. 

S + can / can't (can not) + verb 

They can play soccer very well.
Mark can't understand French.
Birds can fly.

(?) + can + S + verb

Where can I park my car?
Can you speak Spanish?
When can I speak to the doctor?

be able to

'Be able to' conjugates the main verb 'be' rather than a modal verb. 

S + be + able to + verb 

Anna is able to work five days a week.
They aren't able to come to the meeting next week.
He is able to speak three languages. 

(?) + be + S + able to + verb

When are you able to come next week?
Is she able to help us on the project?
What are you able to do?

Modal Verbs of Permission

'Can' and 'May' are all used to ask for and give (or deny) permission to do something.

can

S + can / can't (can not) + verb 

She can stay with us.
They can't use those tools. I'm sorry.
We can use their lawnmower.

Can + S + verb

Many people feel that the modal 'can' should not be used to ask for permission. However, it is commonly used by many English speakers despite the incorrect usage. When using 'can' to ask for permission, do not use question words such as 'what', 'where', etc. 

Can I use your telephone?
Can I have something to drink?
Can she use your car today?

NOTE: 'Could' - the past of 'can' - is also used as a more polite form.

may

'May' is considered by many the only modal to use when asking for permission. The negative form is rarely used. However, the negative form is sometimes used to emphasize that someone does not have permission to do something. 

S + may / may not + verb 

You may start the test now.
You may not go out with your friends this Saturday.
He may see the doctor now. 

May + S + verb

'May' is usually used with only the pronoun 'I' to ask for permission in a polite manner. 

May I use your telephone?
May I ask him a few questions?
May I leave now?

Modal Verbs of Obligation

Modal verbs of obligation are used to speak about something that is required. The two forms - 'must' and 'have to' -  are used in very different ways. 

must

Use 'must' to speak about strong personal obligation at the moment of speaking. This form can be used instead of 'have to'. However, 'have to' is much more common when speaking about daily responsibilities. 'Must' is very strong and should be used carefully.

S + must + verb 

It's late! I must get going.
She must finish her test before twelve.
I must speak to Tom today. It's really important.

s + mustn't (must not) + verb

The negative 'mustn't' is used to speak about actions that are prohibited. 

She mustn't play with those toys.
We mustn't leave before the end of the class.
They mustn't use the computers.

Must + S + verb

The question form with 'must' is rarely used. However, it is sometimes used to complain about something that is required of someone. 

Must I do my homework now?
Must we do this test today?
Must she really leave this week?

S + have to + verb

'Have to' is conjugated as a regular verb with helping verbs (do, did, will, etc.) to speak about daily responsibilities. It is often used to speak about work on a day to day basis, but can be used to speak about specific events. 

She has to get up at seven every morning.
They have to deliver packages on time.
We have to finish the report soon. 

(?) + Auxiliary Verb + S + have to + verb

Does she have to work on this project with me?
Where do we have to go this afternoon?
When does Mary have to get up?

S + don't / doesn't / didn't / won't, etc. + have to + verb

Use the negative to state what is not required, but use 'mustn't' to discuss what is prohibited.

She doesn't have to get up early on Saturdays.
We don't have to worry about arriving late.
They don't have to stay after school today.