Crammerで苦しめられた何通りの意味もあるこの助動詞。General Drのブラジリアンのクラスメイトでさえ頭を抱えていました。
may
1 polite request
2 formal permission
3 less than 50% certainty
might
1 less than 50% certainty
(2 very polite request)
should
1 advisability
2 90% certainty(expectation)/ex She should do well on the test.(future only)
ought to
1 advisability(more formal or British)
2 90% certainty/ex She ought to do well on the test.(future only)
had better
1 advisability with threat of bad result
be supposed to
1 expectation
2 unfulfilled expectation
must
1 strong necessity
2 prohibition
3 95% certainty(present only)
have to
1 necessity
2 lack of necessity(negative)
have got to
1 necessity
will
1 100% certainty
2 willingness
3 polite request
be going to
1 100% certainty(prediction)
2 define plan(intention)
3 unfulfilled intention
can
(more physical)
1 ability/possibility
2 informal permission≒may
3 informal polite request
4 impossibility(negative only)
could
1 past ability
2 polite request
3 suggestion(affirmative only)
4 less than 50%certainty
5 impossibility
be able to
1 ability(≠possibility)
would
1 polite request
2 preference/ex I would rather go to the park than stay home.
3 repeated action in the past
4 polite for "want"
5 unfulfilled wish
used to
1 repeated action in the past
2 past situation that no longer exists
shall
1 polite question to make a suggestion
2 future with "I"or "we" as subject
ちなみに
Can I borrow your pen?
より
May I borrow your pen?
のほうが丁寧表現。
may は50%の確かさ
mightは20%くらいの確かさ