e.g. If you like Picasso, you ought to enjoy the exhibition.

recommendation (can use should)

e.g. You ought to have more driving lessons before you take the test.

criticism (can use should)

e.g. You ought not to shout at your m other like that.

don't have to when you don't need to do something (but you can if you want)

e.g. You don't have to go to school if you don't want to.

have (got) to necessity, impersonal, not for personal feelings, but f or a rule or situation. If you are unsure whether to use must or have to, it is usually safer to use have to.

e.g. I have to get up early tomorrow to catch the train to the office.

must not prohibition (ne gative order)

e.g. You must not leave the table until you have finished your dinner.

need as a normal verb

e.g. Do you need me to help you?

in questions (less usual)

e.g. Need you make so much mess?

needn't not necessary to do something (unusual)

e.g. You needn't come to the party if you don't want to.

don't need to not necessary to do something (more used than needn't)

e.g. You don't need to come t o the party if y ou don't want to.

Summary:

1. What are Modal Verbs?

Modal auxiliary verbs help other verbs express a meaning or an idea but have no meaning by themselves. In English, modal auxiliary verbs are defective; for example, they do not have participle forms (no -ing or -ed endings).

　　They are used in a variety of grammatical moods such as the conditional mood, which expresses uncertainty ("I would be delighted if you came to my party").

　　Modal verbs are special verbs which behave very differently from normal verbs. Next are some important differences.

2. Modal verbs do not take "-s" in the third person.

EXAMPLES:

He can speak Chinese.

She should be here by 9:00.

3. 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.

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