这是我以前写的一篇东东，现在把它放在这里，算作该问题的解答。

交际英语中常用“过去式”表示“现在”

在交际用语中，人们为了表示礼貌或客气，常用would, could, might，表达现在的婉转请求、建议、疑问或看法。例如：

1. would 过去式表示现在或将来：

Would you please do me a favor?

Would you mind if I opened the door?

I’d appreciate it if you could be quiet.

Wouldn’t it be great if you explained the reason to us?

有些动词包括情态动词，其过去时态表示现在的情况，属于一种委婉表达。除了would之外，could和might也同样可以用来表达现在的婉转请求、建议、疑问或看法。例如：

2. could 过去式表示现在或将来：

Could you tell me the way to the station? 请告诉我去车站的路好吗？

Could I speak to you in private a moment, John? 约翰，我可以单独跟你说一会儿话吗

Oh, how could you be so stupid? 哎呀，你怎么这么蠢啊！

It's boring to walk all alone. Couldn't you go for walks with your friends? 一个人走路很没意思。你可以和朋友们一起去散步呀？

3. might 过去式表示现在或将来：

Might I ask what you're doing here? 我可不可以问一下，您在这里干什么？

You might as well bring me a chocolate next time.你下次最好给我带块巧克力来。

The paper says that it might rain tomorrow. 报上说明天可能下雨。

I have got a lot of books that might interest you. 我有许多书，也许你感兴趣呢。

The drivers, as you might imagine, don’t care much about that. 和想象中的一样，这些司机对此并不太在意。

【比较】

Could I use your telephone? （意味着I'm not sure if you will allow me to use your phone.)

Might I use your telephone? （意味着If I don't break it, would you mind my using your phone?) 

【注意】would, could, might 不表示过去，而表达现在的“婉转请求、建议、疑问或看法”，必须是有语境的。以下句子would, could, might 则是表过去。

My son could read and write when he was four.我的儿子在4岁时就能读能写了。

He couldn’t have made such a mistake that day. 那天他不能犯这样的错误。

Reed told me he might be late. 瑞德告诉我他可能会迟到。

She opened the windows so that the fresh air might come through. 她打开窗户以便让新鲜空气进来。

She said she would take care of the child. 她说她愿意照顾那个孩子。

Mum would tell us stories before we went to bed. 过去妈妈在我们上床睡觉前总给我们讲故事。

4. 此外，一些表示“想法，愿望”的动词，如：wonder, hope, think, want 等，它们的过去式可以表示现在婉转的想法或愿望。

I was wondering if you could lend me a hand. （是现在的委婉建议）

We hoped you would do us a favor now. （指现在婉转的希望）

I thought you might like this flower.（指现在的情况，但不敢肯定。） 

I wanted to ask you a question now.（担心对方不给回答，属于婉转。）

Did you wish to see me at present? （属现在的委婉请求。）