Learn English – Is “must” ever grammatical as a past tense verb


I have seen uses of must that appear to be in the simple past tense. Sometimes these seem grammatical, but sometimes not. Examples that help illustrate my confusion:

He knew he must go to New York – sounds fine to me.

He went to New York because he must – sounds questionable.

Because he must go to New York, he bought plane tickets – sounds completely ungrammatical.

He must go to New York – grammatical, but with no other verbs to provide context, can't interpret this as being past-tense.

My question: is this past-tense use of must ever acceptable? Is it only acceptable in certain contexts – if so, what are those contexts and why?

(Note – I'm not looking for had to. Have is a different verb, so had to expresses the same meaning as the past tense of must, but it itself is not the past tense of must.)

Best Answer

Rarely, must is used as a past tense. Belshazzar, by H. Rider Haggard, has we went because we must, in a prose style which is perhaps deliberately archaic to reflect the ancient Egyptian context.

In this odd snippet, If Thoreau went because he would, Hawthorne went because he must, one might say the author is "playing with language".

But here's Ralph Waldo Emerson with What he did, he did because he must. I would not wish to say Emerson doesn't know his own language.

From comments under @Henry's answer, it seems something quite odd has been going on. Many people will know the archaic present tense mote because Freemasons & such still say So mote it be in a "ritual" context. Bizarrely, the past tense "must" eclipsed "mote" for present tense usage. But in so doing, "must" somehow almost completely lost its ability to still be used as a past tense.

In spite of all the above, ordinary mortals in ordinary contexts today should stick with the standard position put forward by other answers. Use had to for the past tense.

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