modal auxiliaries

Does the modal auxiliary forme change?

No, it stay the same.

What is the modale auxiliary form

Modal + base form of the verb : He should consider his options

Modal who’s function is to express an ability

Can

Modal who’s function is to express a polite request

May, would, could, can

Modal who’s function is to express an advice or opinion

Should, ought to

Modal who’s function is to express an obligation

Must , have to

Modal who’s function is to express a probability

Must

Modal who’s function is to express a possibility

Could, might, may

Modal who’s function is to express à condition, desire/preference, past habit

Would, would like, would rather

Must vs Have to

They both indicate that something is necessary but, must not mean that something is not permitted. Don’t have to mean that they can do it if they want to but they shouldn’t.

Past form of must when it’s necessary

Had to

Past form of must when it’s a probability

Must have been

Past form of should, could, and would

Add have + the past participle

Question form with modal auxiliary

Put it before the subject. Have to is an exception, put do, does or do then the subject then the modal