will, would, must, can, can't, could, couldn't	Certainty or near certainty about; now, the future or generally
will have, won't have, would have, wouldn't have, must have, can't have, couldn't have	Certainty or near certainty about the past
should, shouldn't, ought to, oughtn't to, may/might well (not), could well, might easily	Probability about now, the future or generally
should have, shouldn't have, ought to have, oughtn't to have, may/might well (not) have	Probability about the past
could, may (not), might, mightn't, may/might/could just	Possibility about now, the future or generally
could have, may (not) have, might have, mightn't have	Possibility about the real past