语法知识要点：.doc

语法知识要点： 被动语态 英语中的语态分主动语态和被动语态两种。但只有及物动词、动词短语和某些成语才 能构成被动语态。被动语态的构成形式一般为“be十动词的 ed分词”。在下列情况下可用被动语态：不知道或不必要提出动作的执行者；强调动作的承受者；“get十动词ed分词”是被动语态的特殊形式；某些系动词用主动表示被动。表示状态或特征的及物动词没有被动语态。 被动语志由“助动词 be十动词的 ed分词”构成，其时态由 be的不同时态变 化表现，常用的8种被动时态中的变化形式如下表： 时态 现在 过去 将来 过去将来 一般 am is written are was were written will be written would should be written 进行 am is being written are was were being written 完成 has have been written had been written 被动语态的用法 当我们不知道动作的执行者时。例如： He was robbed in the street. Many secrets are concealed. The University was founded 100 years ago. He was seen stealing. 当我们不必要指出动作执行者时。例如： The windows were broken yesterday. The problem had already been discovered by then. This tool can be made very easily by hand. 当我们强调或侧重动作执行者时，通常用by引出动作执行者。例如： It is well known that the ebb and flow are caused by the moon. The temperature of the earth is determined by the amount of solar heat which the atmosphere can keep. I was showed round the school by Bill. 主动形式表示被动意义 某些系动词例如cook, feel, write, smell, taste , sell 等用其主动形式表示被动意义。 1.Cotton feels soft. 2.All the tickets have sold out. 3.It smells terrible. Good medicine tastes bitter. This food cooks fast. [好煮] 没有被动语态的动词 有些动词必须使用主动形式，例如; The story took place two day ago. The earth consists of land and water. The plague broke out in Africa. 必须用被动形式的动词，例如： The article is composed of three parts. 有些动词既可以使用主动形式又可以使用被动形式。例如： He exposes himself to all kinds of opinions. / He is exposed to all kinds of opinions. He devoted himself to the project. / He was devoted to the project. He dresses himself / is dressed every morning. 虚拟语气 语气由一种动词形式来表达，用以表示说话者的意图或态度。虚拟语气表示说话者的 主观愿望、假想或建议等。所说的话有的与现在事实相反，或与过去事实相反，或与将来事实相反，也许表示与将来事实可能相反等等。所以虚拟语气往往与假设条件句用在一起，而虚拟的语言环境，可以由if条件句引出，还可以是其他常见的没有if的条件句或短语。有时，虚拟语气是由上下文环境创造的，没有明显的标志。另外，有时条件从句与结果主句表示的时间不一致, 便形成了错综复杂的条件句。虚拟语气有时还可倒装。除了与条件句在一起使用的主句用虚拟语气外，有些宾语从句、表语从句或同位语从句也时有虚拟。 虚拟条件句的形式与基本