In Modals^x, American English^x, Difference between^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...

1. Use of present perfect tense and simple past tense Speakers of American English generally use the present perfect tense (have/has + past participle) far less than speakers of British English. In spoken American English it is very common to use the simple past tense as an alternative in...