Known 既是 know 的过去分词，又是常见的形容词。当 known 作形容词时，与 to、as 和 for 的连用常常让人扑朔迷离，很多人甚至经常把它们互换使用，其实它们还是有很大的区别。
一般来说 be known as 表示某人或某物因什么而被知道，意为“被称为”，通常是某种具有特殊含义的身份标识，例如：His name is Robert, but he is known as Bobby.She was known as the Iron Lady.Christopher is commonly known as Kit.This design came to be known as the Oriental style.Internet addresses are also known as URLs.
1. 当 be known to 中的 to 作不定式的标识时，表示某人或某物因自己的某个动作或状态特性而被知道，意为“众所周知”等，例如：This drug is known to have adverse side effects.The drug is known to cause a mild cardiac seizure.He was known to eat the same restaurant every Thursday.She was known to cancel interviews at the last minute.2. 当 be known to 中的 to 作介词时，后面通常跟人，表示已经某事情已经被某人知道，意为“为…所知”，例如：He wants to keep them all in his office for reasons best known to himself.他想把他们都留在他的办公室里，原因只有他自己知道。The suspect's violent past was known to police.Rabies has been described as one of the most terrifying diseases known to man.
Be known for 是三个中最好理解的一个，意为“因…而出名”，是一个褒义的短语，通常指某人的成就或某物的特征使某人或某物为众人所知，例如：He is better known for his film and TV work.She is best known for her work on the human brain.The French are known for their love of their language.This plant has long been known for its medicinal qualities.
需要引起注意的是，并不是所有的 known for 都意为“因…而出名”，特别是 for 后面接的一个时间段，它表示的某种状态（已知的，未知的）持续了一段时间，常用于否定句中，因此要根据具体的上下文来判断，例如：
The answer to that question may not be known for days.
这个问题的答案可能好几天都没人知道。
The true cost of these experiments to the environment will not be known for years to come.
这些实验对环境造成的真正损失在未来几年内还不得而知。
四、思考题
1. He is known _____ the police because of his previous criminal record.
a. as
b. to
c. for
2. The director is known _____ his first film.
a. as
b. to
c. for
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