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Hi,

I think Clive mentioned something to the effect that the word 'must' could be used in past-time situations. Could the word 'must' used in past-time situations only for reported speech cases or just about any situations?

He went into the house. There was none. "Either Mary must left or went to sleep,." he thought. Since no one was there, he closed the door and went out.

He went into the house. There was none. The situation could be that Mary must left or went to sleep. He pondered over the choices, but couldn't figure out which one is correct. Confused, he closed the door and went out of the house. -- Can I make the underlined part "Mary must have left"? I think Clive said something about this in another post but could not locate it.
Comments  
He went into the house. There was no one (there). Mary must have either left or gone to sleep. He pondered over the choices...

This use of "must" has a kind of "story-telling" feel, which is OK in this context. It may not always be appropriate though.
Thank you.

Which one is correct?

Yesterday, I went to my friend's house. He wasn't there. I thought he must either (have either???) went out or went to bed.
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I thought he must have gone out.

I thought he must have gone to bed.

Therefore,

I thought he must have either gone out or gone to bed.

Most people would also be happy with "I thought he must either have gone out or gone to bed", even though, being ultra-pedantic, this is in my view illogical. (Doing it this way, it should really be "I thought he must either have gone out or have gone to bed".)
AnonymousCould the word 'must' used in past-time situations only for reported speech cases or just about any situations?
It's probably most used in the reported speech situation or in other subordinate clauses. It's hard to find a main clause where must has a past tense meaning. had to is used instead when the meaning is have to. must have is used when the meaning is the only logical conclusion is....

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must as have to:
I must go. = I have to go.
The past is I had to go.
Present: George must find a way to solve the problem. Or: George has to find a way to solve the problem.
Past: George had to find a way to solve the problem. Not: George must find a way to solve the problem.
Present: You must learn the irregular verbs of English. Or: You have to learn the irregular verbs of English.
Past: You had to learn the irregular verbs of English. Not: You must learn the irregular verbs of English.
Present: Employees must wash their hands frequently. Or: Employees have to wash their hands frequently.
Past: Employees had to wash their hands frequently. Not: Employees must wash their hands frequently.
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must as The only logical conclusion is
Mary has ten cats.
Mary must like cats. = The only logical conclusion is that Mary likes cats.
The past means The only logical conclusion is that Mary liked cats. And for that meaning you have to change must like to must have liked, thus:
Mary had ten cats. She must have liked cats.
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Here are a few more for you to study.
It looks like Lucy is going to leave that package behind. It must be too heavy to carry. (We conclude that it is too heavy.)

Lucy left that big package behind. It must have been too heavy to carry. (We conclude that it was too heavy.)
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The puppy is begging for food. He must be hungry. (We conclude that he is hungry.)
The puppy was begging for food. He must have been hungry. (We conclude that he was hungry.)
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Mr. Johnson buys his wife expensive presents. He must love her very much. (We conclude that he loves her.)
Mr. Johnson used to buy his wife expensive presents. He must have loved her very much. (We conclude that he loved her.)
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Be careful when the main verb is have. must have is the present, and must have had the past.

Aunt Polly always sees when Huck steals a biscuit. She must have eyes in the back of her head!
Aunt Polly saw Huck steal a biscuit. She must have had eyes in the back of her head!
CJ
So what you need in your examples is as follows:
He went into his house. There was nobody there. Mary must have left. (Never: Mary must left.)
must is always followed by a bare infinitive. must be, must leave, must go, must arrive, must see, must have.

must have is always followed by a past participle: must have been, must have left, must have gone, must have arrived, must have seen, must have had.

CJ
P.S. Save posts that have good information. You might even consider taking a hard copy. Then you won't be rummaging around the forum trying to find them later! Emotion: smile
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Older works use must in the past:
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The Mill on the Floss - Page 171

by George Eliot - 1860 - 464 pages

He thought he must go to the study where the pupils were, but on his way he met Mr.
Stelling, who had heard from his wife that Maggie appeared to be in ...

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