英语语法知识整理
一、系动词：
系动词又叫联系动词，是联系主语和表语的成分，有时候在句子中的意思不翻译，有的系动词也有实际的意义。
系动词通常分为be系动词和非be系动词，be系动词通常就是am，is，are。非be系动词主要分为以下几种：
1.、感官系动词
感官系动词通常翻译成“...起来”，例如,look , sound, taste, smell...
2.、渐变系动词
渐变系动词通常翻译成“变得...”，例如， turn, become, get, grow,go
3.、持续系动词
保持系动词通常翻译成“保持...”，表示状态不变，例如，be，remain，keep
系动词的用法：
1.、非be系动词不能拿来直接做句型转换。
2.、系动词后面往往跟形容词做表语，而普通的实意动词后面都是跟副词做状语
二、情态动词+ have +过去分词的用法：
1) may(might) have + done sth, can (could) have + done sth 表示过去，推测过去时间里可能发生的事情。
Philip may (might) have been hurt seriously in the car accident.
Philip can (could) have been hurt seriously in the car accident.
2)must have +done sth，对过去时间里可能发生的事情的推测，语气较强，具有"肯定"，"谅必"的意思。
---Linda has gone to work, but her bicycle is still here.
---She must have gone by bus.
3) ought to have done sth, should have done sth
本应该做某事，而事实上并没有做。否定句表示"不该做某事而做了"。
You ought to (should) have been more careful in this experiment.
He ought not to have thrown the old clothes away.（事实上已扔了。）
ought to 在语气上比should 要强。
4) needn't have done sth 本没必要做某事
I dressed very warmly for the trip, but I needn't have done so. The weather was hot.
5) would like to have done sth 本打算做某事
I would like to have read the article, but I was very busy then.
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