1. can / could not … too 表示“无论怎样也不过分”。例如：
You cannot be too careful when crossing the street. 穿越马路时，再怎么小心也不为过。
You can never be too careful in performing an experiment. 做实验越仔细越好。
2. can / could not be + enough 意为“无论怎么都不够”，表示强烈的肯定。例如：
I cannot thank you enough. 我对你感激不尽。
You can't be careful enough. 你越小心越好。
3. too … not to 表示“太……不会不……”，具有肯定意义。例如：
He is too careful not to have noticed it.
他那么小心，一定会注意到这一点的。
4. never too … to 是对 too … to 的再否定，表示肯定。例如：
It's never too old to learn. 活到老，学到老。
5. not … for nothing 中， not 用来否定 for nothing ，从而加强了谓语的肯定意义。例如：
He didn't study law for nothing. 他学法律并没有白费。
Believe me， he did not fly into such a rage for nothing.
请相信我，他勃然大怒是有原因的。
6. nothing if not 表示“极其”，含强烈的肯定意义。例如：
He was nothing if not clever. 他很聪明。
The story was nothing if not interesting. 故事极其有趣。
7. nothing less than 表示“完全是”，有肯定的含义。例如：
What he said was nothing less than a lie. 他说的纯属谎言。
His negligence was nothing less than criminal.
他的粗心大意无异于犯罪。
8. nothing but 表示“只有;只不过”，含肯定意义。例如：
We could see nothing but water. 我们只看见一大片水。
She does nothing but listen to records.
她除了听唱片什么也不做。
9. no 的否定意义很强，和具有否定意义的名词连用，来表示强烈的肯定。例如：
She is no fool. (She is very clever.) 她绝不是傻瓜。
There is no question that Mr. Smith is the boss.
毫无疑问，史密斯先生就是老板。
10. 双重否定表示强烈的肯定。例如：
Nobody had nothing to eat. = Everyone has something to eat. 每个人都有吃的。
11. not … until/till 表示“直到……才”，具有肯定的意义。例如：
She didn't stop working until it was 12 o'clock last night.
昨晚 12 点以前，她一直在不停地工作。
12. “否定词 + so + adj. /adv. + as ”结构从反面表示“最”，是一种强烈的肯定。例如：
It wasn't so bad as last time! 这次不像上次那么坏!
None is so blind as those who won't see.
没有比视而不见的人更瞎眼的了。
13. 有些带否定词的短语，在使用时并不构成否定意义，即表示肯定意义。例如：
He would go as soon as not. 他非常乐意去。
As often as not the buses are late on foggy days.
遇多雾天气时，公共汽车经常晚点。
14. 否定的感叹句、疑问句常表示肯定意义。例如：
Isn't this film interesting? 这电影难道没趣吗?
Who doesn't enjoy reading The Dream of the Red Mansion?
谁不喜欢看《红楼梦》呢?(人人都喜欢看《红楼梦》。)
15. 以 why don't you do 和 why not do 开头的疑问句往往表示邀请、建议、指导等，具有肯定意义。例如：
Why don't you introduce her to your parents?
你为什么不介绍她给你父母认识?
Why not come and see me tomorrow?
明天找我怎么样?
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