①只做情态动词:must,can,may……
②可做情态动词又可做实义动词：如：need,
dare
③具有情态动词特征：have(had,has)
to,used
to,
ought
to
④可做情态动词又可作助动词：如：shall(should),will(would)[
注意
mustn't代表强烈禁止
must表示主观，have
to表示客观。
美式英语中常用must
not
而不用
mustn't.
mayn't,mightn't和shan't也很少用
常用
can
(could),
may
(might),
must,
need,
ought
to,
dare
(dared),
shall
(should),
will
(would)
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