~だったかもしれない
may have ,might have,could have
~だったはずがない
can't have,couldn't have
~してはいけない
must not ,may not
~しても良い
can,may
たぶん~だろう、~なのも分かる
may well,might well
~しても良いだろう
消極的な感じ
may as well, might as well
~しさえすれば良い
have only to
have toと同じ意味
have got to
ought to の否定
ought not to
had betterの否定
had better not
~するべきだった
should have
~だったに違いない
must have
~することになっている、~なはずだ
be supposed to