In Modals^x, American English^x, Negations^x

I am trying to formulate guidelines for learners of English as a foreign language with regards the use of may/might/could to express possibility. It seems to me that you can use these three modals (almost) interchangeably when expressing possibility. For example, 'Where's Mary?' 'I'm not...

CalifJim wrote: Why must expresses epistemic modality -- it must be the mailman, and must not carries only deontic modality Not to spoil the argument you're making here, but to clarify a tangential matter: This is not true for American English, which allows the following: -- Janette is not...