英语语法里面很重要的一部分，是句子的构成。
概说
1、任何一个句子一定由主语（Subject，简写成S）及动词（Verb，简写成V）构成。
例：John works hard. （约翰努力工作。）
S V
He plays the piano well. （他钢琴弹得很好。）
S V
Mary seems to be fond of learning English. （玛丽似乎喜欢学习英语。）
S V
2、（1）有时主语可以省略，而构成祈使句。这种祈使句由原形动词（也称为动词不定式）引出。
例：Work hard! = （You should）work hard.（努力工作！）
原形V
Be quiet! =（You should）be quiet. （安静！）
原形V
（2）祈使句变成否定型式时，要在原形动词前加 Don’t。
例：Don’t fool around. （别游手好闲。）
Don’t be silly. （别傻了。）
可充当主语的词类
一般所见到的句型中，通常是以名词做主语，但除了名词以外，还可以用代词、动词转变过来的动名词或不定式短语、名词从句、名词短语、表距离的地点副词短语等做主语。
介绍如下：
一、名词做主语
例：The child is apt to tell lies.
（这孩子喜欢说谎。）
Gold is of much value.
（黄金很值钱。）
二、代词做主语
例：He always keeps his promise.
（他总是信守承诺。）
It is quite interesting to climb mountains.
（爬山蛮好玩的。）
三、动名词或不定式短语做主语
动词绝不可直接充当主语，一定要变成动名词或不定式短语，如此才可视为名词的对等语，当主语用。
例：See him makes me angry. （×，See为动词）
→Seeing him makes me angry. （○，Seeing为动名词）
（看到他就让我生气。）
See him is my purpose of coming here. （×，See为动词）
→To see him is my purpose of coming here. （○，To See为不定式）
（我来这儿是为了看他。）
1．动名词做主语
用动名词做主语，通常用以表示已知的事实或经验。
试译下句中的主语：
集邮是他的嗜好之一。
由“嗜好”一词得知，此处的“集邮”乃是一种经验。
故应译成动名词 Collecting Stamps，而成：
Collecting stamps is one of his hobbies.
再译下句中的主语：
听音乐使我快乐。
由“使我快乐”得知，“听音乐”是说话者曾经做过的事，故仍用动名词短语Listening to music 做主语，而成：
Listening to music makes me happy.
2．不定式做主语
用不定式做主语时，通常表示一种意愿、目的或未完成的事。
试译下句中的主语：
出国念书是我最大的愿望。
由“愿望”一词得知此处的“出国念书”乃是一种意愿或尚未做的事，故应以不定式短语 To study abroad 充当主语，而成：
To study abroad is my greatest desire.
（出国念书是我最大的心愿。）
再译下句中的主语：
到日本游玩是我今年的计划。
由“计划”一词得知说话者尚未到过日本游玩（go to Japan for a visit）,故此处用不定式短语 to go to Japan for a visit 做主语，而成：
To go to Japan for a visit is my plan for this year.
注意：不定式或动名词短语做主语时，往往会形成主语过大的现象，故通常均用代词it做主语，置于句首，而将真主语（亦即不定式或动名词短语）移至句尾。动名词移至句尾时，通常改为不定式短语。
例：Collecting stamps is one of his hobbies.
= It is one of his hobbies to collect stamps.
虚主语 真主语
Listening to music makes me happy.
= It makes me happy to listen to music.
虚主语 真主语
To study abroad is my greatest desire.
= It is my greatest desire to study abroad.
虚主语 真主语
注：虚主语相当于传统语法中的形式主语。
注意：被it代替的动名词短语移至句尾，仍保留动名词形态而不变成不定式短语。但此种用法并不普遍，初学语法者宜尽量避免。
例：It is interesting to learn English. （佳）
It is interesting learning English. （劣）
注意：以下句型则属例外情形，it要代替动名词短语，不可使用不定式短语：
It is no use 动名词短语例：It is no use crying over spilt milk.
(覆水难收。)
It is no use asking him for help.
(向他求救是没有用的。)
注意：
It is no use 动名词短语
= It is useless 不定式短语
= It is of no use 不定式短语
use
= There is no sense in 动名词短语
point
例：It is useless to cry over spilt milk.
= It is of no use to cry over spilt milk.
= There is no use in crying over spilt milk.
四、名词从句做主语
1．名词从句
他不用功令我生气。
这个句子的主语虽然是“他不用功”，但若译成 He doesn’t work hard，则大错特错。
He doesn’t work hard makes me angry. （×）
因为 He doesn’t work hard 是句子。所谓句子，就是一开头就是主语的结构（此处的He就是主语）。句子绝不能当主语，一定要变成名词从句方可做主语。
故本句的正确译法应为：
That he doesn’t work hard makes me angry. （○）
名词从句
2．名词从句的种类
名词从句一共有三种：that从句、whether从句、疑问词所引导的从句
（1）that从句
任何一个主语起首的句子前面冠以that即成that从句。
He doesn’t believe my words.
→ that he doesn’t believe my words
（他不相信我说的话。）
He enjoys dancing.
→ that he enjoys dancing
（他爱跳舞。）
There is much work to do.
→ that there is much work to do.
（有很多工作要做。）
（2）whether从句
本从句是由可用yes/no回答的问句变化而成。
① 问句有be动词时：
主语与be动词还原，前面冠以whether。
例：Is he happy?
→ whether he is happy
（他是否快乐……）
② 问句有一般助动词（can, will, may, should, ought to, must, have）时：
主语与助动词还原，前面冠以whether。
例：Can he do it?
→ whether he can do it
（他是否能做这件事……）
Has he done it?
→ whether he has done it
（他是否已做好这件事……）
③ 问句有do, does, did等助动词时：
主语与助动词还原，再将do，does，did去掉，后面的动词依人称和时态变化。
例：Did he come?
→ whether he did come
came
（did为过去式，故come改为came）
→ whether he came
（他来不来……）
Does he like it?
→ whether he does like it
likes
（does为第三人称单数现在式，故like改为likes）
→ whether he likes it
（他喜不喜欢它……）
（3）疑问词从句
本从句是由疑问词（when，what，how，where，why）等引导的问句变化而成。
① 问句有be动词时：
主语与be动词还原，前面保留疑问词。
例：What is he doing?
→ what he is doing
（他正在做什么……）
② 问句有一般助动词时：
主语与助动词还原，前面保留疑问词。
例：Where can he find it?
→ where he can find it （他在哪里能找到它……）
③ 问句有do，does，did等助动词时：
主语与助动词还原，前面保留疑问词，再将do，does，did去掉，动词依人称和时态变化。
例：What did he write?
→ what he did write
wrote
（did为过去式，故write改为wrote）
→ what he wrote
（他写什么……）
When did he come?
→ when he did come
came
（did为过去式，故come改为came）
→ when he came
（他何时来……）
How does he do it?
→ how he does do it
does
（does为第三人称单数现在式，故do改为does）
→ how he does it
（他怎么做这件事……）
注意：
who，what，which（哪一个）为疑问代词，若在问句中做主语，变成名词从句时，结构不变。
例：Who came here? 问句
主语
→ who came here 名词从句
（谁来这儿……）
What happened last night? 问句
主语
→ what happened last night
（昨晚发生什么事……）
Which was bought? 问句
主语
→ which was bought 名词从句
（哪个被买走……）
3．名词从句的功能
我们已知，名词从句是由叙述句子或问句变化而成，和动名词或不定式短语一样，名词从句也要被视为名词。由于具有名词的特性，故可做主语、谓语或be动词之后的补语。
（1）名词从句做主语
例：That honesty is the best policy is a proverb (Which) we should always keep in mind.
主语
（“诚实为上策”是一句我们应时时谨记在心的箴言。）
Where he lives is still a doubt.
主语
（他住哪里仍不确定。）
Whether he can do it remains to be seen.
主语
（他能胜任与否仍优待观察。）
注意：
动名词或不定式短语，名词从句做主语时容易造成主语过大的现象，可用代词it代替，置于句首，而被代替的名词从句则置于句尾。
因而上述各例句可改写为：
It is a proverb we should always keep in mind that honesty is the best policy.
It is still a doubt where he lives.
It remains to be seen whether he can do it.
（2）名词从句做动词的宾语
例：I know that he will go abroad in the nearest future.
（我知道他最近即将出国。）
I wonder whether he has finished the work.
（我怀疑他是否已做完工作了。）
（3）名词从句做介词的宾语
注意：
用whether或疑问词引导的名词从句可做宾语，但that从句不可做介词的宾语。
例：I am worried about whether he can do it.
（我很担心他是否能做这件事。）
I am suspicious of how he’ll cope with the problem.
（我怀疑他将如何应付这个问题。）
I am sure of that the team has won the game. （×）
遇有介词，且非要使用that从句时，其补救方法如下：
① 介词＋the fact＋that从句
如此，就可用the fact做介词的宾语，而that从句就成了the fact的同位语。
例：I am sure of the fact that the team has won the game.
（我确定这个队赢了。）
I am worried about the fact that he doesn’t study.
（我很担心他不念书。）
② 保留介词，但不加the fact，且介词之后的that从句要做适当变化
第一步：除去that；
第二步：that之后的主语变成所有格；
第三步：动词变成动名词。
例：I am worried about that he plays around all day.
prep. his playing
→ I am worried about his playing around all day.
（我为他整天游手好闲而担心）
注意：that从句若有助动词do，does，did时，去掉即可。
例：I am worried about that he doesn’t study.
prep. his not studying
→ I am worried about his not studying.
注意：that从句若有助动词will或would时，去掉即可，但也可以改为be going to，再将be动词转变为动名词being。
例：I am sure of that the team will win the game.
prep. the team’s winning
→ I am sure of the team’s winning the game.
或：I am sure of that the team is going to win the game.
prep. the team’s being
→ I am sure of the team’s being going to win the game.
注意：从句若有以下助动词时，做下列变化：
may → be likely to
can → be able to
should
→be supposed to
must
再将be动词变成动名词being。
例：I am happy about that he may come. （×）
→ I am happy about that he is likely to come.
→ I am happy about his being likely to come.
（我很高兴他可能会来。）
I am sure of that he can do it. （×）
→ I am sure of that he is able to do it.
I am sure of his being able to do it.
（我确定他能做这件事。）
I am sure of that he should accept Mary’s advice. （×）
→ I am sure of that he is supposed to accept Mary’s advice.
→ I am sure of his being supposed to accept Mary’s advice.
（我确定他应该会接受玛丽的劝告。）
③ be＋adj.＋that从句
也就是去掉介词，将that从句放在形容词后面，使that从句成为副词从句（注：相当于传统语法中的状语从句），修饰该形容词。
例：→ I am worried that he plays around all day.
adj. 副词从句
I am sure of that the team has won the game.
→ I am sure that the team has won the game.
以上三种用法中以①、③最为普遍，②是常考的一种句型。
有时介词之后也可以直接接that从句，而不需the fact，形成惯用语，同学亦应牢记。
in that = because 因为
例：He is great in that he can speak five different languages.
（他很棒，因为他能说五种语言。）
except that 只可惜
例：He is nice except that sometimes he lies.
（他人很不错，只可惜有时会说谎。）
for all that 尽管
= with all that
= not withstanding that
例：For all that he is nice, I don’t like him.
= Despite the fact that he is nice, I don’t like him.
= In spite of the fact that he is nice, I don’t like him.
（尽管他人好，我却不喜欢他。）
五、名词短语做主语
名词短语是由“疑问词＋不定式短语”构成。
1．疑问副词
where to live （住哪里）
whether to try again （是否再尝试一次）
when to talk to him （什么时候和他谈）
how to do it （如何做它）
2．疑问代词
what to do （做什么）
whom to see （看谁）
which to buy （买哪一个）
whom to talk to （与谁谈）
注意：疑问副词构成的名词短语中，疑问副词因为是副词的性质，故不做不定式短语中及物动词的宾语。但疑问代词构成的名词短语中，疑问代词因具有名词的性质，故一定要做不定式短语中动词或介词的宾语。因此what，whom，which在上述名词短语中，分别做do，see，buy，to（介词）的宾语。
名词短语因具有名词性质，故亦可做主语，是由名词从句简化而成。
例：Where to meet him is not decided yet.
= Where we should meet him is not decided yet.
（在哪里见他还未决定。）
How to handle the problem depends on how much money we can collect.
= How we can handle the problem depends on how much money we can collect.
（我们如何处理这个问题要视我们能募集到多少钱而定。）
六、表距离的地点副词短语做主语
From＋地点名词＋to＋地点名称，此为表距离的地点副词短语，亦可做主语，与单数的be动词并用。
例：From Taipei to Taichung is about 160 kilometers.
（从台北到台中大约160公里）
上面例句中，主语亦可用it代替，而构成下面句子：
It is about 160 kilometers from Taipei to Taichung.
