Must in the past tense

English grammar questions, answered by Alan

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Must in the past tense

Post by McKinney » Mon Nov 05, 2018 2:54 pm


We knew that we must not become exhausted.
I read this sentence in a book and I want to know why "We knew" is in the past but "we must not become exhausted" is in the present.

I know "had to" is usually the past tense of must but "We knew that we had not to become exhausted sounds strange. I'm lost!

Thank you! :-D

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Re: Must in the past tense

Post by Alan » Wed Nov 07, 2018 4:24 am

A very good question!

'Must' is in fact, in origin, a past tense (cognate with Modern German "musste" = had to). The corresponding present form disappeared from usage centuries ago, on account of which the past form began to take over the functions of the obsolete present, with the result that nowadays 'must' in a main clause is invariably present.

However, in subordinate clauses it can still function as its own past tense, hence the example you cite.

Just for reference, 'had not to become' would be perfectly grammatical, but sounds archaic and is generally avoided in daily speech.