KManchester: Grammar: Modals of Obligation (Must/ Have to)

Friday, 6 September 2013

Grammar: Modals of Obligation (Must/ Have to)

We often want to talk about choice. Sometimes we can make a choice but many times we cannot. There are rules and laws that mean we cannot choose to do what we always want to do.

The shop is closing down: the shop will not exist anymore. The shop is selling all its clothes in order to make as much money as possible. It has no choice. All the clothes must be sold. Everything must go!

We use must and have to to talk about choices.
We use must and have to when we have no choice.

Must is a modal verb and modal verbs are always followed by... base forms. Modal verbs never change: they have no third person form. So: I must..., you must..., he must...
Have to is also followed by the base form. Remember that have to changes: I have to..., you have to..., he has to...

The difficult part is the past and the negative.

We use must for the present and future. The past of must is had to.
We use mustn't for negatives. The negative of have to is mustn't.

We often use must in some common expressions:

a must see: "The special effects in the movie are amazing. It really is a must see film."
a must read: "Inferno, by Dan Brown, is this year's must read book."
We also use don't have to/ doesn't have to when we have a choice. The past of don't have to is didn't have to. We can also use don't need to/ doesn't need to/ didn't need to.