Modal Verbs

Type	Modal Verbs	Example
ABILITY	Can, Could	David can speak three languages. He could speak fluent Franch when he was 5.
PERMISSION	Can, Could May	Can i sit in thet chair please? Could I open the window? may I borrow your dictionary?
ADVICE	Should	You should visit your dentist at least twice a year. You should try to lose weight.
OBLIGATION	Most, Have To	I must memorize all of these rules about tenses. You have to take of your shoes before you get into teh mosque.
POSSIBILITY	Might, May, Could, Can	It Looks nice,but it might be very expensive. Richard may be coming to see us tomorrow.

Modals are different from normal verbs:

1: They don't use an 's' for the third person singular.

2: They make questions by inversion ('she can go' becomes 'can she go?').

3: They are followed directly by the infinitive of another verb (without 'to').

Probability:

First, they can be used when we want to say how sure we are that something happened / is happening / will happen. We often call these 'modals of deduction' or 'speculation' or 'certainty' or 'probability'.

For example:

Ability

We use 'can' and 'could' to talk about a skill or ability.

For example:

Obligation and Advice

We can use verbs such as 'must' or 'should' to say when something is necessary or unnecessary, or to give advice.

For example:

Permission

We can use verbs such as 'can', 'could' and 'may' to ask for and give permission. We also use modal verbs to say something is not allowed.

For example:

Habits

We can use 'will' and 'would' to talk about habits or things we usually do, or did in the past.

For example:

Past modals

The past modals 'could have + past participle', 'should have + past participle' and 'would have + past participle' can be confusing. I explain about them here.