我以前的上司（美国人）辞职回美国了，走之前还不忘告诉我们说任何话时，一定要用tentative的语气。

所谓tentative语气，字面上的意思就是「试探性」的语气，也就是不要把话说死，给自己留一点余地。

注意tentative 不等于 uncertain的语气，注意和maybe这种语气区分开来。

比如多用seem, appear, sound, look这样的词。

例如:

This is wrong 改成 This seems to be wrong.

We don't have other option 改成 It seems we don't have other option.

反正在下结论的时候（哪怕明明是很确定的事情)，记得加一个seems, appears，语气没那么生硬。

另外，一个东西，明明很好，硬要说looks good, sounds good，而不是It's good.

以下还要注意的几点

1）不要总是说maybe这种话，如果确定性比较大的情况下，用probably（实在不行改成seem也好）

比较

例一

Maybe this is rightThis is probably right.

例二

Could we have a better way to do it?

Maybe(有些敷衍）.

Probably.

中国人滥用maybe，不管什么情况都用maybe，给人一种毫无把握的感觉。在表示有很可能的时候，老外都用probably。maybe是比较不确定。

如果想表示“我很可能是错的”用I'm probably wrong.

2）给别人提供建议时，不要用should，也不要you'd better，而是用It would be better

比较

This design should be changed.It would be better if we can change the design.

3）表示一件事希望你做，但是不强求时，用It would be nice/great 而不是 I need you to xxx, I hope you xxxx, could you?

比较

I hope you can come today.

You need to come today.

Could you come today?

It would be nice/great if you can come today. (隐含的意思是still OK if you can't make it.)

再举个例子

比较

Can you bring some wine to the party?

It would be nice/great if you can bring some wine to the party. 

4）问别人你要东西/ 信息时，用May I have...? 而不要Could you give me?

比较

例一

What's your name?May I have your name?

例二

Could you send me the drawing today?

May I have the drawing today?

例三 《血战钢锯岭》里，法官要老Doss把那封信给他，他是说 May I have the letter ？而不是Could you give me the letter?

例四 问别人有没有时间

Could I have a minute/moment of your time?（非常非常礼貌，销售员问法）

Do you have a minute/moment??（一般礼貌，同事朋友之间问法）

例五 你比如你想独处一下，比如想打个私人电话，要别人回避一下。

Could you come out?Could I have a moment(for myself)?

5) 问别人是否可以做一件事时，用 Is it possible that...比Could you ..更礼貌

比较

例一

Could you change the design?Is it possible for you to change the design?

例二

Could you call me tomorrow?Is it possible for you to call tomorrow?

6) 请别人帮忙做一件事时，在前面加(by) any chance，意思是如果有时间/有机会，很委婉。

By any chance, could you help check the data? 有时间可不可以帮忙看看数据？

7) 指责别人时候，用现在进行时比一般现在时要更委婉。

比较

你很没耐心/强词夺理/无理取闹

You are impatient/argumentative/unreasonable.

You are being impatient//argumentative/unreasonable

说前者会得罪很多人，因为你用一个 are 就把别人完全说死了，正常的说法是用being，这样表示某时某刻这个人处于的状态,不表示你把他彻底说死。

8) 表达要求时多用进行时。

比较

We need to do this as soon as possible.

We need to be doing this as soon as possible.

老外普遍用后者用的多。

以上两种情况中，如果不用进行时，就有表示永久去做这件事的意思，用进行时就可以委婉表示我们会进入这种状况，不是永久的。