1、只做情态动词:may, might, must…
2、可做情态动词又可做实义动词:如:need, dare.can...
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)
5、mustnt代表强烈禁止, must表示主观,是自发的,have to表示客观,意为不得不去做某事。
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6、美式英语中常用must not 而不用 mustnt. maynt,mightnt和shant也很少用
7、常用:can (could), may (might), must, need, ought to, dare (dared), shall (should), will (would)