■ know

1) know 是个延续状态（第一类动词），“知之为知之，不知为不知”，不是指“从不知到知”的变化（不是表示“得悉”、“获悉”、“弄熟悉”的第四类动词）。如果指的是变化，要改用 learn，或者说 get to know。

• We got to know (*knew) each other.我们彼此熟悉了。
• Only at that moment did we learn (*know) that she had already left.到了那个时刻，我们才知道她已经动身走了。
• With the small classes, I really got to know my professors and the subject... Also I got to know my classmates really well; we all know each other by name.开了小班，我就真正认识了老师们和科目。…我也真正地熟悉了同班的同学；现在我们都以名字互相认识。
• You should get to know/learn (*know) more about your own country. 你应该更多了解自己本国（know 是“已经知道”的状态，而且是不能主动去做的事，不能劝告人家去做，但是祈使句 Know your enemy.是个例外）。

但是 know 偶尔也可以借用作第四类动词，表示“从不知到知”的变化，亦即“得悉”，相当于 learn 或 get to know，如：

• Suddenly I knew.

2) 不可以仿效“I hope so.”或“I think so.”说“*I know so.”，而只能说“I know it.”或“I know that.”。

3) to know of 某人、某物或某事，是间接听闻或肤浅的认识；to know 某人是同某人见过面，有交情；to know about 某事则是对之有具体的了解。

• I know of the mountain, but I've never climbed it.我听说过这座山，但从来没有爬过。
• I know of him, but I don't know him personally.我听说过他，但是我不直接认识他。

4) know that... 是知道某事；know + 间接问句，是对后面的疑问知道答案。

• Do you know when we should go there?你知道我们该什么时候到那边去吗？
• I don't know (I'd like to know) whether he passed the examination.我不知道（我想知道）他考试是不是及格了。

know that 后面必须是说话者认为真确的事实，所以逻辑上不能说 *I don't know that..., 但可以说 I don't know whether... 如果说话者明明知道 that 从句的内容是错误的，也不能说 know that，例如不能说：*John knows that the capital of Australia is Sydney. 但是可以说：John believes that the capital of Australia is Sydney.

5) know somebody to inf., 这个动词不定式只能是 to be（还有表示“拥有”或“具备”的 to have），而且只能指经常的状态。

• I know her to be a reliable person.我知道她是个可靠的人。
• I know him to be a liar.我知道他是个好撒谎的人。

如果是一时的状态，用这个结构就不大自然。

• *I know him to be ill.我知道他病了。

除了 to be 和 to have （have 是实义动词，作为助动词见下面一节，用其他动词都不妥。

• You know him to be honest.你知道他是正派的。
• I know him to be a very decent guy.我知道他是个十分规矩的人。
• I know him to have a keen eye for these things.我知道他对这些事情很有眼光。

6) 但是，to know somebody 后面的动词不定式，如果不是 to inf. 而是 to have + pp，则这个动词就不局限在 to be 与 to have 这两个动词，而且也不局限在经常的状态，甚至可以指一次的行动（第二、三、四类动词）或一时的状态（第一类动词）。

• I know him to have been a very good chief.我知道他曾经是个很好的领头人。
• Everybody knows him to have been wrongly accused, and, in innocence, destroyed.人人都知道他是被冤枉而且无辜被毁了的。
• We know them to have failed in business.我们知道他们做生意失败了。
• I know him to have received an injury while shoeing a horse in the fall of 1863.我知道他曾于 1863 年秋天给一匹马钉蹄铁时受了伤。
• I know him to have been born 1931 in Chicago.我知道他 1931 年生于芝加哥。

7) 此外，know 如果是过去时或现在完成时，作为“看到”“获悉”的一个经验，就可以用 knew (或 have known) somebody to inf. 的结构，而且后面这个不定式动词既可以是经常的状态，也可以是一时的状态甚至是一时的动作。

• Did you ever know her to be unkind to any one? (Raymond Macdonald Alden, The Castle Under the Sea) 你曾经发现她对谁凶过吗？ Did you ever know her to be afraid of anything? (ibid.)你曾经发现她有什么害怕的吗？
• Ever since my son was born I have known him to be different.我儿子出生以来，我就一直觉得他不寻常。
• However, I have known him to sit in his study with pencil in hand and paper before him, scarcely shifting his position for five or six hours.但是，我就曾经知道他坐在书房里，手里拿着铅笔，面前摆着纸张，五六个钟头不改变一下姿势。
• I have known him to read forty-eight hours without stopping.我就曾经知道他看书一看就是四十八小时不停。

8) Did you know...? 与 Do you know...? 的区别是：Do you know...? 是真正的提问，提问者真的想了解对方究竟知道不知道（know 后面往往跟着 about 或是间接特殊问句）。

• Do you know what to do in case of fire?你知道遇到火灾该怎么办吗？
• Do you know when we should go there?你知道咱们什么时候要到那边去吗？

而 Did you know...? 可以说是个用来告诉对方某个新闻的开场白或幌子，后面往往是以 that 从句表示的现成答案（常常是一些奇谈珍闻）。说 Do you know...? 是单刀直入的，较少考虑对方的面子，而 Did you know...? 则不好意思假定对方可能不知道，所以用过去时，暗示对方本来可能已经知道。

• Did you know that the word "byte" is a contraction of "by eight" and "pixel" a contraction of "picture cell"?你知道吗？“byte”这个单词是“by eight”的缩略，“pixel”是“picture cell”的缩略。
• Did you know? In North America, bats are the most endangered land mammal.你知道吗？在北美洲，蝙蝠是最濒临灭绝的陆地哺乳动物。

9) know better 有否定意义，意思是“心里知道不是这么一回事”。

• Although his female colleagues insisted the gray only accentuated his bookish appeal, Langdon knew better. (Dan Brown, The Da Vinci Code, p.8)尽管朗顿的女同事们坚持认为灰色只会更加衬托出他的书呆子气质，但是他自己却心中有数。

如果认为某人对自己撒谎，就对这个人说：You know better. 意思就是“你自己心里明知道不是这样的。”

10) know 后面还可以接上过去分词，表示“知道自己处于某种状态”。

• She knew offered good protection.她知道人家给她提供了很周到的保护（即 She knew that she was being offered good protection = She knew that someone was offering her good protection.）。

11) Don't I know it! 表面上是否定，其实是肯定，表示“我知道得一清二楚”。

• —You seem to be putting on a little weight. —Don't I know it! —你看来体重增加了些。—我知道得很清楚。

12) know 还可以在个别搭配中表示“具有”（属第一类动词）。

• His ambition knows no bounds.他的野心永无止境。

也可以表示“经历”（属第四类动词）。

• This area knows a shower only once every ten years.这个地区每十年才有那么一场阵雨。
• The country has never known an earthquake.这个国家从未发生过地震。
• I have known both poverty and wealth.我穷困和富有的经历都有过。
• She has known what it is like to be poor.她尝过穷困的滋味。
• His uncle has known better days.他的伯父现在潦倒了。