英语中表示请求或许可的情态动词

在疑问句中，主语是第一人称，表示请求别人允许的情态动词有can, could, may, might, 且从左至右越来越正式或客气，越来越不那么常用。如：

—I hear you’ve got a set of valuable Australian coin. ________ I have a look?

—Yes, certainly. (北京春)

A. Do                                                  B. May

C. Shall                                                D. Should

【分析】答案选B。may表示请求对方允许，即：“我可以做……吗?”

使用时还需注意以下4点：

■表示允许或者不允许时，可用于任何人称，但不能用could, might。如：

1. A left-luggage office is a place where bags ________ be left for a short time, especially at a railway station. (全国卷)

A. should                                              B. can

C. must                                                D. will

【分析】答案选B。can表示“可以”。should(应该), must(必须), will(愿意)均不符语境。

2. —Will you stay for lunch?

—Sorry, ________. My brother is coming to see me. (全国卷)

A. I mustn’t                                         B. I can’t

C. I needn’t                                          D. I won’t

【分析】答案选B。can’t不可以。家兄要来这一客观情况“不允许”我在这吃饭。mustn’t 语气太强；needn’t(不必)和won’t(不愿)均不得体。

3. —Could I borrow your dictionary?

—Yes, of course you ________. (全国卷)

A. might                                              B. will

C. can                                                 D. should

【分析】答案选C。允许别人做某事时，不可用could, might，可用can, may。表示不允许别人做某事时，可以说No, you can’t / may not / mustn’t. (不可以)，还可以用I’m afraid not. (恐怕不行)，I’d rather you didn’t. (我希望你不)，Certainly not. (当然不行)等来回答。礼貌地拒绝对方的请求时，还可以伴以某种说明。如I’m afraid you can’t because…

■当迫切要求得到肯定答复时，往往用can’t和couldn’t来代替can和could。但不用或很少用May I not…? Mayn’t I…? Might I not…? 如：

—Mum, I’ve been studying English since 8 o’clock. ________ I go out and play with Tom for a while?

—No, I’m afraid not. Besides it’s raining outside now. (辽宁卷)

A. Can’t                                               B. Wouldn’t

C. May not                                           D. Won’t

【分析】答案选A。迫切要求得到肯定答复用Can’t I…? 另外，可用Won’t / Wouldn’t / Will / Would you…?来询问对方是否愿意做某事，但却没有Won’t / Wouldn’t / Will / Would I…?的说法。

■表示客气的请求的方式还有：Do you think I could / might use your phone? 或I wonder if I could / might use your phone?等。

■主语是第二人称，可用Can / Could you…?但不说May / Might you…?如：

How ________ you say that you really understand the whole story if you have covered only a part of the article? (上海卷)

A. can                                                  B. must

C. need                                                 D. may

【分析】答案选A。can在疑问句中，表示疑惑、怀疑，可译作“可以”。答案B和C意义不通，答案D的may，不能用于may you…?