教师在学生作文中经常见到非谓语动词使用错误的语句，例如：Live in big cities is bad for people's health.或者Internet has two sides include advantages and disadvantages. 以上错句都是由于不会运用非谓语动词的缘故，导致一个句子含有两个或多个谓语动词，违背了英语中一个句子通常不能有两个或两个以上谓语动词的原则（除非动词是并列谓语）。

首先，我们要先了解什么是非谓语动词。非谓语动词就是在句子中不作谓语，而是充当主语、宾语、表语、定语、状语和补语的词，主要包括不定式（to do）、动名词（doing）、现在分词（doing）和过去分词（done）四种情况。其中动名词和现在分词形式一样，都是动词的ing形式，但却是表示不同的两个概念。动名词是充当名词作用的词，现在分词、过去分词和不定式是充当形容词或副词作用的词。

1. 非谓语动词作主语成分

动名词（doing）和不定式（to do）可以作主语。不定式表示具体的某一次行为或未发生的动作，动名词表示习惯性或正在做的动作。Living in big cities is bad for people's health.一句中动名词Living in big cities作主语。 To punish a very young child is both wrong and foolish, as an infant will not understand what is happening or why he or she is being punished.一句中不定式to punish a very young child作主语。注意他们作主语时，谓语动词是单数。其中，不定式作主语时，句子头重脚轻，所以通常用it 做形式主语，把不定式放在后面，而不定式其实才是真正的主语，所以有了固定搭配It is… to do…。例如：It is quite common these days for young people in many countries to have a break from studying after graduating from high school.在这句话中，it做形式主语，而真正的主语是to have a break from studying after graduating from high school。

2. 非谓语动词作主语和表语成分

动名词和不定式也可放在be动词后面作表语。例如：The first step in the cement production is to put limestone and clay on two different conveyors. 一句中不定式 to put limestone and clay on two different conveyors作表语。One example of an activity that is easy for most people is swimming. 一句中动名词swimming作表语。

3. 非谓语动词作宾语成分

动名词和不定式还可放在实义动词后面作宾语。例如：Young adults tend to rely on their parents for help when buying a house. 一句中不定式作宾语。Many people, and children in particular, enjoy playing computer games. 一句中动名词作宾语。“V. + to do”和“V. + doing”结构的灵活运用需要学生在平时多积累类似于“tend to do”和“enjoy doing”这样的后面跟不定式或动名词的动词。

4. 非谓语动词作定语成分

写作中常用作定语的非谓语动词是现在分词（doing）和过去分词（done）。其中，现在分词作定语，修饰先行词时，表示主动且正在进行的动作。过去分词作定语，表示被动且已完成的动作。这两种形式，本质上算是定语从句的部分省略形式。比如：Those consisting of only one parent or a single adult had almost double this proportion of poor people, with 21% and 19% respectively.在这个句子中 consisting of only one parent or a single adult是现在分词作定语，修饰先行词those，实际上这句话可以还原为Those which are consisting of only one parent or a single adult had almost double this proportion of poor people, with 21% and 19% respectively.

过去分词作定语的情况也有很多，比如：Water used in the industrial and domestic sectors also increased, but the consumption was minimal until mid-century.在这个句子中used in the industrial and domestic sectors就是过去分词短语修饰先行词water作后置定语，water与use使用的关系为被动关系，水被使用。实际上可以还原成which is used in the industrial and domestic sectors。

4.非谓语动词作状语成分

现在分词、过去分词和不定式可作状语。其中现在分词和过去分词作状语表示原因、时间、条件、让步、结果等，可以转换为对应的状语从句。例如：The biggest gender difference is at the lowest post-school level, where 90% of those who held a skilled vocational diploma were men, compared with only 10% of women.其中compared with only 10% of women 作状语，表示比较，这里是男性被和女性进行对比，是被动关系，用过去分词。再看一个现在分词作状语的情况：Between these years electricity production almost doubled, rising from 100 units to 170 in Australia, and from 90 to 180 units in France。其中rising from 100 units to 170 in Australia, and from 90 to 180 units in France是现在分词作状语，表示伴随。

动词不定式作状语常常表示目的。例如：To help a child learn the difference between right and wrong, teachers and parents should firstly provide good role modelling in the their own behavior.  一句中to help a child learn the difference between right and wrong是目的状语，有时也可以用in order to或者so as to强调目的，例如：In order to buy an apartment and raise children, people have to spend most of their time on work.

如果学生能够掌握非谓语动词的使用规律和常用用法，并在写作中正确地使用它，也能帮助大家形成英语表达的思维，同时增加句子表达的多样性。如果在写作时想用从句时，不妨看看能否可以用非谓语动词代替从句，这样能使文章语言更简练。