核心问题
（1) Could you come and see me when you are next in London? [《高中英语教科书》第二册(下),人教社,p.69]
(2) Could I drop in at your house after the concert, or would that be too late? (同上, p. 69) 上面的句子表达的是现在的情况,为什么助动词要用过去时呢?
词典解答
在英语里有一种所谓的礼貌过去时(the attitudinal past):
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Did you want to see me now?
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Could I speak to Sue?
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Might I have a little brandy?
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Would you help us?
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I wondered if you could help me.
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I was wondering if you could help me.
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Should I open the window?
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I wonder if you could look after my child while I am away.
这里使用过去时只是为了表示礼貌，使口气显得委婉、谦逊，而与过去的时间毫不相干。因此在回答中，如果仍保留情态动词的话，一般要换成现在式。句1的回答：Yes，I do. 句2的回答是：Yes，you can (could). 句3的回答是：Yes，you may. 句4的回答：Yes，I will. might 与 could 的区别：前者更有试探性，语体更加正式(参见 may )。