●情态动词有其独特的用法，例如，shall只能用在第一人称里。
●由主动语态变成被动语态，或由被动语态变成主动语态时，有的情态动词的意思会发生变化。比较下面的例句：
I can’t do it. 我不能做这件事。
I cant’t be done by me. 这件事不可能由我来做。
The Passive of Infinitives and gerunds 不定式和动名词的被动语态
Infinitives 不定式不定式的被动语态的形式如下所示：
(not) to be + 动词的过去分词
我们常用不定式的被动语态。比较一下下文里主动语态和被动语态的句子。
I would like someone to tell me the truth. 我希望有人能告诉我实情。
" I would like to be told the truth. 我希望能被告知实情。
They want us to pick them up at half past eight.他们希望我们8点半去接他们。
" They want to be picked up at half past eight.我们希望8点半被接。
I asked them to fet6ch me in the morning.我告诉他们早上来接我。
" I asked to be fetched in the morning.我要求早上来人接我。
*美国英语里一般常用pick up。
I asked them to pick me up in the morning. "I asked to be picked up in the morning.
不定式的被动语态常用来表示义务，特别是规则，规定常用这种形式。
Ties are to be worn at all times.领带要一直系着。
Every visitor is to be treated with respect. 每一个访问者都受到礼待。
Gerund 动名词
动名词的被动语态如下所示。
(not )being +动词的过去分词
第六单元的“语法博士DR GRAMMAR”里列举的接-ing形式的动词大部分都可以用动名词的被动语态。
If you want to avoid being sacked, be nice to the boss.如果你不想被开除，对老板好一点。
I can’t bear being ignored.我不能容忍被忽视。
Did you enjoy being shown round the factory?你喜欢有人带着参观一下工厂吗？
第七单元列举的加介词的动词和和介词+宾语+-ing形式，也可以用动名词的被动语态。
I object to being should at.我讨厌别人对我喊叫。
There’s no point in his being sent home.把他送回家毫无意义。
