语法重难点之现在分词作状语

   非谓语动词作状语使用频率很高，其中现在分词作状语在英语学习中是一个重点，也是一个较为复杂的难点。现在分词在句子中充当状语时其逻辑主语必须与整个句子的主语保持一致，可表示时间、原因、目的、条件、结果、方式、伴随、让步和评价，相当于一个状语从句。

一、现在分词作时间状语

  现在分词作时间状语，按照分词动作与谓语动作发生的先后，可以分为以下三种情况：

（1）现在分词表示的动作一发生，谓语动词表示的动作立即发生，这时用作时间状语的现在分词用一般式，多置于句首。这种情况所表达的含义可以换成由as soon as或when引导的时间状语从句，该从句的动词多用一般过去时。例如：

  Hearing his mother’s voice, Robert turned off his computer at once.(= As soon as he heard his mother’s voice, Robert turned off his computer at once.) 或者(= When he heard his mother’s voice, Robert turned off his computer at once.)

（2）现在分词的一般式所表示的动作与谓语动所表示的动作同时发生，可以在现在分词前加上when或while表示强调，这时可转换成 when、while引导的时间状语从句，该从句的谓语动词用进行时态。例如：

  When multitasking, the brain is concentrating on one task and then switching to the other, in sequence.(= When / While it is multitasking, the brain is concentrating on one task and then switching to the other,in sequence.)

（3）谓语动词表示的动作发生在现在分词所表示的动作之后，现在分词用完成式，即 having done的形式。此时相当于after+ doing结构，也可以用after，when引导的时间状语从句来替换，该从句的谓语动词用过去完成时。例如：

  Having reviewed hundreds of applications from around the world, the judges settled on a design by Jurgen Mayer.(= After reviewing hundreds of applications from around the world, the judges settled on a design by Jurgen Mayer.) 或者(= After / when they had reviewed hundreds of applications from around the world, the judges settled on a design by Jurgen Mayer.)

二、现在分词作原因状语

  现在分词作原因状语时，一般置于句首，相当于because,since或as所引导的原因状语从句，此时也要注意分词所表示的动作与谓语动作的先后关系。当分词所表示的动作与谓语动作同时发生或几乎同时发生时，分词用一般式，从句谓语动词用一般过去时。例如：

  Depending on the distance the information has to travel, the reaction time of the robotic arms can be delayed slightly, and computer compatibility can be an issue as well.(= Because it depends on the distance the information has to travel, the reaction time of the robotic arms can be delayed slightly, and computer compatibility can be an issue as well. )

  当分词表示的动作发生在谓语动作之前，分词要用完成式，从句谓语动词用完成时。

  Having lost her job, she had to look for another one．(= As she had lost her job, she had to look for another one. )

三、现在分词作条件状语

  现在分词作条件状语时，一般放句首，相当于if、unless、once引导的条件状语从句，谓语动词常用一般将来时态。例如：

Working hard, you will succeed.(= If you work hard, you will succeed.)

四、.现在分词作结果状语

  现在分词作状语时，表示一种自然而然或符合逻辑的结果，通常放在句尾，其前常有thus，thereby等表示结果意义的词，相当于 so that 引导的结果状语从句。作结果状语的现在分词的逻辑主语可以是句子的主语，也可以是前面的整个句子。在前一种情况下，现在分词短语相当于由and连接的并列谓语；在后一种情况下现在分词短语相当于一个非限制性定语从句。例如：

  The child fell, (thus) striking his head against the door. (= The child fell and struck his head against the door.)On the fire,it heated up, turned black, and finally exploded, causing a loud “boom” and frightening everyone nearby.(= On the fire,it heated up,turned black,and finally exploded, which caused a loud “boom” and frightening everyone nearby.)

五、现在分词作方式状语

  现在分词作方式状语时表示行为方式或补充说明，既可放在句首，也可放在句尾，相当于一个由and连接的并列句。

  Using tiny GPS devices, scientists conducted several different experiments to learn more about hoe Egyptian fruit bats navigate.(= Scientists used tiny GPS devices and conducted several different experiments to learn more about hoe Egyptian fruit bats navigate.)Chinese chemists began to experiment, combining chemical substances to make louder, more powerful explosions.(= Chinese chemists began to experiment and combined chemical substances to make louder, more powerful explosions.)

六、现在分词作伴随状语

  现在分词作伴随状语表示分词表示的动作与句子谓语动词所表示动作同时进行，由同一个主语发出，分词既可放在句首，也可放在句尾，相当于并列句。例如：

  High-tech monitors around the room beep and buzz, measuring oxygen in take, heart rate, and blood pressure.(= High-tech monitors around the room beep and buzz and are measuring oxygen in take, heart rate, and blood pressure.)We sat exhausted on our backpacks, awaiting the arrival of our instructors to transport us home.(= We sat exhausted on our backpacks and were awaiting the arrival of our instructors to transport us home.)