6.4. Grammar. Modal verbs in the past.

This is another problematic area in English because many of the above modal verbs are impossible in the past.


Let’s look first at must and have to.

What is the past of HAVE TO?

That’s relatively simple; it’s had to.


What about must and have got to?

Not so easy. There is no past form. You need to look for an alternative verb that has the same meaning. The only thing in English that means the same thing is had to. So you can use either without problems, but only in the positive forms.

As you will remember, in their negative forms, mustn’t and don’t have to have completely different meanings.

Mustn’t means ‘it is important that you don’t…’; don’t have to means ‘you can if you want, but there’s no obligation’. 

It isn’t possible to use one single word for both these ideas.


Don’t have to in the past is simply didn’t have to.

Haven’t got to has no past tense. Mustn’t (like must) has no past form either.

You need another completely different verb, which expresses prohibition. Which?

You can’t think of one can you?

You will have to use a structure like to not be allowed to, to not be permitted or to be prohibited (from + gerund).

Some students use couldn’t which is more or less correct, but can cause confusion as it is also used for inability (‘She couldn’t swim.’); suggestions (‘Couldn’t you invite him to the party tomorrow?’); and to express many other ideas.

Compare: ‘We weren’t allowed to watch the Benny Hill Show when we were younger. My parents thought it was too rude’ and ‘We couldn’t watch the Benny Hill Show when we were younger. We didn’t have a TV.’


Can in the past is usually could, especially when it refers to permission and ability. There are irregular cases that we will look at in more detail in 11.1. 11.4. 

May not, when it is used in formal situations for obligation has no past tense either.

‘She may not leave the court until she has paid the fine.’ In the past you would have to say, ‘She wasn’t allowed…’



In conclusion, we can say that this is an area that needs much practice, as you have to learn two completely different sets of rules for present and past. Spend time studying it because these structures often mean ‘it’s important that you do/don’t…’ ‘it’s not very important that you do/don’t…’

One little mistake can completely change the meaning of a sentence. Compare;  ‘You mustn’t answer all the questions.’ ’You don’t have to answer all the questions.’