Section_ⅢGrammar-_情态动词(Ⅱ)

　　语法图解

　　探究发现

　　①By now his restaurant ought to be full of people.

　　②Does your father need any help?

　　③What do we need to take for the picnic?

　　④You needn't try to explain.

　　 ⑤His mother is ill.He has to stay at home to look after her.

　　⑥Something terrible must have happened if Li Chang was not coming to eat in his restaurant as he always did.

　　[我的发现]

　　(1)以上句子中，第①④⑤⑥句中的黑体词都是情态动词，而第②③两句中的黑体词是实义动词。

　　(2)以上各句中的情态动词后都接动词原形。其中第⑥句中must have happened的意思是"一定已经发生了"。

　　(3)上述句子中ought to意为"应该"；need意为"需要"；has to意为"不得不"。

　　一、ought to的用法

　　1．"应该"，表示责任或义务。用于表示按道理应当，常指客观的义务或责任，大多数情况下可用should代替，但比should语气重。

　　You ought to study harder than your brother.

　　你应该比你哥哥更努力学习。

　　I should help her because she is in trouble.

她有困难了，我应该帮助她。