cannot but do/cannot help but do/cannot help doing

这三个短语在意义上基本相同,都表示“禁不住”“不由得”“不得不”“不能不”的意思,但用法和语体有区别。cannot help 之后跟动名词,是最规范的用法,因此最为常见(为所有的英语辞典所收纳),并常见于标准英语考试中:

1. I can't help admiring the picture whenever I look at it. (EC) 不管我什么时候看到这幅画,我都禁不住要赞赏它。

2. Harry could not help feeling a definite sense of anticlimax. (J. K. Rowling, Harry Potter and the Deathly Hallows) 哈利忍不住感到一种深深的失落。(《哈利·波特与死亡圣徒》)

3. I couldn't help thinking that if Jesus had this much of a sense of humor, being a Christian wasn't going to be so tough. (B. Clinton, My Life) 我忍不住想,如果耶稣这么有幽默感,那么当个基督教徒也不会太难。(《我的生活》)

cannot but 后面要跟不带 to 的不定式。这种用法不大规范。不少语言学家认为是个不好的用法。但是我们不时还是能见到这种用法：

1. I cannot but admire your decision. 我不能不赞赏你的决定。

2. One's world outlook cannot but come through in what one says and does. 一个人的世界观必然在其言行中表现出来。

3. I cannot but admire the truth of your remarks, although they go against my interests. (LDCE) 我不能不欣赏你的话的真实性,尽管它们违背我的利益。

cannot help but 后面也要跟不带 to 的不定式。这种用法多见于非正式语体。语言学家们（如 Hornby 以及 RWRT 的作者们）认为它是合乎语言习惯的。而且托福试题也采用了这种句式，见 can $^{14}$ 之托福试题。

1. You can't help but respect them. 你禁不住会尊敬他们。

2. When the streets are full of melting snow, you can't help but get your shoes wet. 当街道满是融化的雪水时，你是不能不把鞋子弄湿的。

3. Harry could not help but agree with the unknown Thicknesses. (J. K. Rowling, Harry Potter and the Deathly Hallows) 哈利无可奈何只好服从那个他从没听过的塞克里斯。(《哈利·波特与死亡圣徒》)