MODAL VERBS

All the auxiliary verbs are called modals; they cannot act alone as the main verb in a sentence.

IN SHORT:

Can

Can I smoke here?

We can’t fix it.

Ability / Possibility /Inability / Impossibility Asking for permission Request

Could

We could try to fix it ourselves.

Could I borrow your dictionary?

I think we could have another Gulf War.

Asking for permission/Request /Suggestion/ Future possibility/ Ability in the past

May

May I have another cup of coffee?

China may become a major economic power

Asking for permission Future possibility -

Might

We'd better phone tomorrow, they might be eating their dinner now. -

They might give us a 10% discount.

Present possibility/ Future possibility

Must

We must say good-bye now.

They mustn’t disrupt the work more than necessary.

Necessity / Obligation/ Prohibition

Should

We should sort out this problem at once.

I think we should check everything again.

Saying what’s right or correct /Recommending action / Uncertain prediction

What are Modal Verbs?

Modal verbs are special verbs which behave very differently from normal verbs.
1. Modal verbs do not take "-s" in the third person.

Examples:

He can speak Chinese.
She should be here by 9:00.
2. You use "not" to make modal verbs negative, even in Simple Present and Simple Past.

Examples:
He should not be late.
They might not come to the party.
3. They make questions by inversion Examples:she can go' becomes 'can she go?'. 4. Many modal verbs cannot be used in the past tenses or the future tenses.

Examples:

He will can go with us. Not Correct
She musted study very hard. Not Correct

They convey different meanings:

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'.

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

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

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.

Past modals:
The past modals 'could have + past participle', 'should have + past participle' and 'would have + past participle' can be confusing.