while
1.while（连接词）作“当…的时候”解。例如：
It was raining while we were out.
While he was reading, he heard his father call him.
while不可指一点时间（a point of time），如不可说：
He rang me up while he heard of his brother's arrival.
While I had finished my letter, I posted it.
这两句里的while都该改作when。
2.下面两句里的while表示对比（contrast），有(al)though的意思：
While this is true of some, it is not true of all.
While I like the story, I do not like the English.
3.While he was reading, he heard his father call him里的he was可以省去。但While I like the story, I do not like the English里的I like不可改作liking，因为liking只能代表I am liking，不能代表I like（参见though 3）。下面三句都不可说：
While being ready to help him, I wondered what he needed most. （该把being删去，或把While删去而把being改作Being）
The house, while being a very old one, is still kept in good repair. （该把being删去，或把while删去，或把while being删去）
While admitting that the idea is a very good one, we are sorry we are not in a position to carry it out. （该把admitting改作we admit）
4.在2里所讲的while表示对比（参见2）。while决不可表示原因，如下面两句都不对，该把While改作As或Since：
While he is perfectly honest, we all love him.
While you cannot go with me, I have to go alone.
5.while不可用作and then解，如下面三句都不对，该把while改作when：
I was about to start while it began to rain.
He was going to bed, while a letter came.
The case was heard yesterday, while she did her best to defend herself.
6.while用作动词只用在while away（闲混过）his（或her等）time，while away many afternoons等表达方式里，后面接现在分词，不接不定式。例如：He whiled away his time talking or walking. 和The children whiled away many afternoons playing on the beach.