How should I use 'must' in past tense?

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I suppose the modal verb 'must' works like below:

  1. I am sure that he is busy. → He must be busy.
  2. I am sure that he was busy. → He must have been busy.

I want to know how 'must' itself changes in past tense like this:

  1. I was sure that he was busy. → ?

Thunderweb

Posted 2015-02-25T00:34:06.960

Reputation: 73

1Are you asking about "I must do this now" vs "I * had to* do that yesterday"? – Jim – 2015-02-25T03:04:30.247

Yes, I want to know how a sentence with 'must' changes into past tense. And I think 'had to' is not appropriate in this case... or is it? – Thunderweb – 2015-02-25T04:12:13.610

Answers

2

As the past tense of "must" is also "must" (identical in form) the modal must is normally used only in present tense to avoid ambiguity. When you need the past tense you have to use forms of substitution verbs.

"must2" (the past tense form) can be used only in very limited cases. It may occur sometimes in written language in subordinate clauses. I think learners should not try to handle must2.

In most cases the modal must is given only with one form (present tense).

rogermue

Posted 2015-02-25T00:34:06.960

Reputation: 8 304

3

As rogermue points out "must" is the same for both past and present. To indicate something happened in the past, you would just add additional information that contains a recognizable time frame.

I was sure that he was busy. → I thought he must have been busy

Andrew

Posted 2015-02-25T00:34:06.960

Reputation: 85 521

What's about combination of verbs? "He must have done it" works? – Judicious Allure – 2019-06-09T19:58:04.517

0

I must do it(present tense) I had to/was to do it(past tense)

rafi ur rashid

Posted 2015-02-25T00:34:06.960

Reputation: 535