情态动词表推测时，英语中只使用must,may,might,和can't。

这五个表达的语气依次递减：

must:一定（语气肯定）

may：也许（不很肯定）

might：或许（比may语气更弱）

can't：一定不（must的反义）

推测现在的事情用must,may,might和can't do或be

e.g.She must be at home now.

The boy may play now.

推测过去的事情用must,may,might和can't have done

e.g.She might have been ill yesterday.

He must have hold the party.

注意：表推测的must,may,might和can't是不可以与I think...连用。因为I think...已有推测的含义，故不能连用。

用以上的思维导图，理解更容易。