Question

What exactly is the past tense of the modal auxiliary must not?

Answer 1

@umm

Answer 2

Modal verbs are defined by their inability to conjugate for tense and the third person singular

Answer 3

But there must be some kind of past form so that it can be used in a sentence in past tense.
Like... there is had to which is the past tense of must. I am not sure what it is for must not though

Answer 4

All modals must have a sentence that has must have, would have, could have, may have, might have, and so forth and on.

So, for past tense, it'd be similar to the modal itself, here's an example. `I would have taken the cookie yesterday when there was a chance.`