Past and future tense of 'must'

[Mairi]

I am having a bit of trouble finding any rules about the past and future tesne of must. Using the word must in a future tense and past tense sentence is easy enough..

he must go to the doctor (f)
he must have gone to the doctor (p)

The word must changes it's tense with the use of auxiliary verbs.

Is it as simple and as straight forward as that? Do i need to explain that the negative of must is 'mustn't'?

Any advice on how to explain this to EFL students would be great. Thanks.

 

[bhaisahab]

I am having a bit of trouble finding any rules about the past and future tesne of must. Using the word must in a future tense and past tense sentence is easy enough..

He must go to the doctor. (f) This is not a future tense sentence.
He must have gone to the doctor. (p) This is not a past tense sentence.

The word must changes it's tense with the use of auxiliary verbs.

Is it as simple and as straightforward ("straightforward" is one word) as that? No. Do I need to explain that the negative of must is 'mustn't'?

Any advice on how to explain this to EFL students would be great. Thanks.

.

 

[e2e4]

:shock:

 

[Johnson_F]

'Must' is effectively the present tense form of a modal verb. Because of the nature of one of its meanings (roughly: be obliged to), what one is obliged to do usually happens after the obligation is imposed:

He must (present obligation) go (in the future) to the doctor.

Like all modals, 'must' has no future form; we have to use an alternative way of expressing the idea, for example:

He will have to (future obligation) visit the doctor.

'Must' has no past tense form; once again, we have to use an alternative way of expressing the idea, for example:

He had to visit the doctor.

Note:
He must not go = He is obliged not to go.
He needn't go/ He doesn't have to go = There is no obligation for him to go.

'Must' can also convey the idea of 'it is a logical assumption that':

He hasn't been to work all week. He must be ill.

If we assume, in the present, something about a past state, we express it thus:

He must have gone to the doctor. = It now seems logically certain that he went to the doctor.