Must — modal auxiliary

Must is a modal auxiliary verb that we use primarily to express obligation, deduction and strong recommendations. Let’s take a closer look at this modal auxiliary verb.

For expressing obligation 

• They must do what is intended for the project.
• Amy must not cross at a red light.
• She mustn’t tell anyone about our secret!

For deducting or expressing what we believe to be certain

• He arrived late to work. The boss must have been annoyed.
• Spain gets really hot so it must be hard during the summer months.
• Our company has increased its income by 20%, therefore, it must be going really strong.

For expressing strong advice, suggestions, or recommendations

• Listen, you must listen to my friend because he knows what he’s talking about.
• You must see the new bar that just opened, it’s amazing!
• The food there is so delicious, you must go one day.

The difference between must and have to

The modal auxiliary verb, must can be substituted for, have to with very little difference in meaning. Have to is only a little more formal than must.

See also