MODAL AUXILIARIES: MUST

MODAL AUXILIARIES

MUST

• To express obligation or strong necessity (as well as HAVE TO or NEED TO):
We must take the bus now. We must use the computer for the project

• To give advice:
You mustn’t give up. She must take an umbrella because it is raining

• To make deductions (HIGH PROBABILITY):
He must be my father. They must be home by now


* The NEGATIVE of Must is constructed with:

DON’T HAVE TO (haven’t is NOT employed) She doesn’t have to study. I didn’t have to tidy my room up yesterday
DON’T NEED TO / NEEDN’T (TO is not employed) He doesn’t need to stay longer. On Sundays, I don’t need to get up early. It needn’t be big but has a garden (not ‘s’ required)


MUSTN’T

• To express strong prohibition (it doesn’t mean lack of obligation or necessity):
We mustn’t use the station all day. You mustn’t smoke in class. Under 18 mustn’t drink spirits


MUST versus HAVE TO

There is a slight difference when employing Must and HAVE TO:

- MUST is employed by authorities (Teachers, Parents, Doctors, Police…):
You must study. You must clean your room. You must stay in bed. You must tell us the truth

- HAVE TO is employed by everybody:
I have to study now. She has to give up her boyfriend. They have to sell the house