连接副词：
可分为两类，一类是用于连接句子或从句，常见的有therefore, otherwise, however, moreover, still, thus, meanwhile等；
另一类是用于引导从句或不定式，主要有when, why, where, how等。
例如：We all tried our best; however, we lost the game. 
            Tell me when we shall leave. 
            I do not know how to find him.

 连接副词的特点：
一、连接句子或从句的连接副词
连接副词的性质类似于并列连词，使用时其前通常用分号或句号；
若其前用逗号，则通常带有并列连词(如and)。如：
I don't like it; besides, it's too expensive. 我不喜欢它，而且也太贵了。
We all tried our best; however, we lost the game. / We all tried our best. However, we lost the game. 我们都已尽了最大的努力，不过我们还是输了。
注意，有的连接副词(如however等)后通常有逗号与句子的其他成分隔开。另外，有的这类副词还可位于句中或句末：
Peter is our youngest child, and we have three others besides. 彼昨是我们最小的孩子，我们另外还有三个孩子。
He may, however, come later. 不过，他也许一会儿就到。
We all tried out best. We lost the game, however. 我们都已尽了最大的努力，不过我们还是输了。

二、引导从句和不定式的连接副词
用于引导从句(名词性从句)或不定式的连接副词主要有when, why, where, how等。如：
Tell me when we shall leave. / Tell me when to leave. 告诉我什么时候离开。
I don't know how I can find him. / I don't know how to find him. 我不知道如何找到他。
Where we can get the money is just our problem. / Where to get the money is just our problem. 到哪里去弄到这笔钱正是我们头痛的事。
That's why he speaks English so well. 那就是他为什么英语讲得这么好的原因。
注：连接副词why 后不能不定式，如可说 I don't know why I must leave.(我不知道我为什么必须离开)，但不能说 I don't know why to leave。

连接副词的句法特征：
所谓连接代词和副词，实际上就是我们以前学过的疑问代词和副词，如who, whose, whom, what, which, when,where, why,how以及由how构成的词组。
1.连接副词起对等连接词的作用,连接两个句子或子句,如:
however, so, then,moreover,concequencely,hence,also,besides,,otherwise,therefore,thus等。
I feel a bit tired. However, I can hold on.我有点累了,但我能坚持下去。
They talked about it for hours. Finally, they decided to go。他们对此商量了好几个小时,最后他们决定去。

2.连接副词通常位于子句的句首,有的也可位于句中。
They talked about it for hours. Finally, they decided to go。他们对此商量了好几个小时,最后他们决定去。
finally作为连接副词,放在句子的句首。
I have never been to Wales. I, therefore, don't know much about it.我从未去过威尔斯,因此我对它知道的不多。
therefore作为连接副词,位于句子的句中。

3.有些连接副词的含义彼此相同或相近,在使用时可以互相替换,而不会改变原句的含义。
The weather was cold. Therefore(Thus), we stayed home.天气寒冷,因此我们待在家里。
therefore和thus的含义相近,因而也可以互相替换。

在应用时要注意以下两点：
一是它们在构成疑问句时叫疑问词，引导宾语从句时称作引导词。
一是它们和that不一样，在从句中有含义，担任相关的句子成分，所以不能省略，另外，它们须放在宾语从句之首，宾语从句必须是陈述句结构。

引导名词性从句的连接词可分为三类：
连接词：that, whether, if, as if, as though（不充当从句的任何成分，但绝不能省略）
连接代词：what, whatever, who, whoever, whom, whomever, whose, which, whichever.
连接副词：when, whenever, where, wherever, how, however, why

不可省略的连词：
1. 介词后的连词
2. 引导主语从句和同位语从句的连词不可省略。
That she was chosen made us very happy.
We heard the news that our team had won.
大部分连接词引导的主语从句都可以置于句末，用 it充当形式主语。
It is not important who will go.
It is still unknown which team will win the match.

并列连词：
主要是用来表示并列关系、选择关系、因果推理关系等。也可用来连接平行的词，词组或分句。

并列连词表示关系及代表实例:
1.表示并列关系
表示并列关系的连词主要含有“和”、“补充”、“增加”等意思。用来表达并列关系的连词有如下几个：
and 和 both...and...二者都
either...or...或者...或者...
neither...nor...既不...也不...
as well as 也、连同
not only...but (also)... 不但...而且...
e.g.
I used to live in Paris and London.
我过去住在伦敦和巴黎。
Both Jane and Jim are interested in pop music.
詹妮和吉姆对流行音乐都很感兴趣。
She is not only kind but also honest.
她不但和蔼而且诚实。
Bob as well as his parents is going on holiday this summer.
鲍勃和他的父母今年夏天要去度假。

2.表示转折关系
常用来表示转折关系的并列连词有如下几个：
but 但是
yet 然而
still 仍然
while 然而
while 然而、偏偏
e.g.
The winter in Beijing is very cold while that of Kunming is warm.
北京的冬天很冷，然而昆明的冬天却很温暖。
I explained twice, still he counldn't understand.
我解释了两遍，然而他却还不懂。

3.表示选择关系
表示选择关系的并列连词：
or 或者
or else 否则
otherwise 否则
neither...nor... 既不...也不...
either...or... 或者...或者...
e.g.
Would you like leave or would you like to stay?
你是想走还是想留？
You can come either on Saturday or on Sunday.
你可以星期六来也可以星期天来。
Neither you nor I nor anyone else believes such things.
不管你我或者其他任何人都不会相信这件事。

4.表示因果推理关系
表示因果关系的并列连词主要有so，for，then，therefore 等。
e.g.
The air here is polluted, so the crops are dying.
这里的空气受到了污染，所以庄稼快死了。
The leaves of the trees are falling, for it's already autumn.
树叶在落下，因为秋天已经到来了。

并列连词注意事项：
并列连词for引导的分句只能放在句尾，前面用逗号隔开，表示补充说明的微弱理由，只是为前面的内容提供判断的理由，有时译为并列的某种形式。
这与because不同，because引导的是一种明确的因果关系，解释原因，常可回答why的提问。
几个特殊并列连词用法：
一、表示并列关系的and，or，well，as，not only...but also... 等连词也有比较活跃的用法。
and 作为并列连词有多重含义，除了可以表示并列关系外，还可以表示顺承、目的、条件、反复等关系。
e.g：He went to market and bought some vegetables.(表示顺承，动作的先后发生）
他到市场买了一些蔬菜。
Come and help me out.(表示目的）
过来帮我一下。
Be careful and you'll make fewer mistakes.(表示条件）
如果仔细，你所犯的错就少。

二、or 与 either...or...
or表示为“否则”的话，前句一般是祈使句，后句用一般将来时。
在表示选择关系时or 与 either...or... 用法相同，但 either...or...更具强调性。
在多个对象进行选择时，可以用A or B or C... , either A or B or C... , neither A or B or C... 。
e.g：Either Jim or Jake or Jeff knows about this.

三、as well as 与not only... but also...
名词+as well as+名词作主语时，强调前面的名词，谓语动词要根据前面的名词而定。
not only...but also...连接名词作主语时，其强调在后者，谓语动词要根据后面的名词而定。
e.g：China as well as many other countries loves peace.
中国与世界上的其他许多国家一样热爱和平。
Not only Bill but also his parents want to go traveling by bike.
不仅比尔而且他的父母都想骑自行车去旅游。
注：当or，neither...nor...，either...or 等连接主语时，谓语动词由or或nor后面的部分而定。
并列连词表示关系:

种类	用法	举例
并列连词	表示转折关系	but, yet等
	表示因果关系	For, so等
	表示并列关系	And, or, either…or, neither…nor, not only.. but also, as well as等

从属连词：
这种连词是用以引导名词性从句定语从句和状语从句的，由从属连词所引导的句子叫从句,而含有从句的句子叫作复合句。

从属连词可分为三大类：
1、that （无词义，不做成分）
if，whether （表达是否的意义，但不做句子成分）
2、连接代词：who，whom，whose，what，which，whatever, whoever, whichever（有词义，在句子中可作主语、表语、宾语）
3、连接副词：when，where，why，how，how many，how long，how far，however，whenever，wherever （有词义，作从句的状语）

用法：
从结构上说，英语连接词分两大类：并列连词和从属连词。

并列连词连接两个或两个以上地位平等的字、词组或分句。例如：
(1) Air and water are indispensable to me. 　　
(2) She likes going out with friends or playing outdoor games. 　　
(3) Most workers have a good income, so they look very happy. 　　

从属连词连接两个或两个以上的分句，形成复杂句中的从属分句。例如： 　　
(4) He said that he did not want to go . 　　
(5) Many things have happened since I last saw him. 　　
(6) You may come if you want to. 　　

从属连词用来连接各种从句。
until(till)直到，在用until表达时间状语的句子中，主句中的动词是要十分小心去选择的。
如动词是持续行动词，它要用肯定句，如：
I studied hard until 12 o'clock last night.
如果动词是瞬间截止性动词，则要用否定句，如:
He didn't go to bed until his mother came back.
由since,for,by,before, 来引导的时间状语从句。
since 引导的时间状语是动作的开始时间，如:
I have studied English since 1990.
而by引导的时间状语通常是动作的结束时间，如：
I had learned 25 English songs by the end of last term.

从属连词语法分类：

种类	语法作用	连词举例
从属连词	引导原因状语从句	Because, since
	引导条件状语从句	If, unless, as long as
	引导目的状语从句	So that
	引导结果状语从句	So…that
	引导方式状语从句	As, just as, as if
	引导让步状语从句	Though, although, even though, no matter what, however, no matter how, whoever, no matter who, wherever, no matter where
	引导比较状语从句	As…as, not so…as, than, less…than, the more…the more
	引导名词性从句	Who, whom, whose, which, that, when, where, why

宾语从句：
在句子中起宾语作用的从句叫做宾语从句。
宾语从句分为三类：动词的宾语从句，介词的宾语从句和形容词的宾语从句。
宾语从句连接代词主要有：
who, whom ,whose ,what ,whoever ,whomever ,whosever, whatever, whichever 等。

宾语从句的特点:
1.宾语从句可以作及物动词、介词及形容词的宾语。
2.宾语从句的语序一律用陈述句语序。
3.连接词that引导宾语从句在句中无词义，不充当句子成份，多数情况下可以省略。
4.whether 和 if 都可引导宾语从句，但 whether后可紧跟or not；whether从句可作介词的宾语。
5.如果从句太长，可以用形式宾语it.

宾语从句的时态:
1.主句是一般现在时，从句根据实际情况使用任何时态。
例句：The headmaster hopes everything goes well.
2.主句是过去时态，从句须用过去时态的某种形式。
例句：She was sorry that she hadn’t finished her work on time.
3.当宾语从句表示的是一个客观真理或者事实时，即使主句是过去时，从句也用一般现在时态。
例句：The teacher told his class that light travels faster than sound.
4. 如果从句的动作发生在主句之前，则从句要用过去完成时态。 

宾语从句的语序:
A. 宾语从句必须用陈述语序。 　　
False: He is wondering when can he finish this difficult job. 　　
Right: He is wondering when he can finish this difficult job.
B. 有时候可以用it 作形式宾语，而把真正的宾语从句放在后面。 　　　
Bad: I thought that he could finish this　job in just two hours impossible. 　　
Good: I thought it impossible that he could finish this job in just two hours.　 
C. 带有宾语从句的复合句的否定形式一般是否定主句。
Bad: I think he doesn’t like the English teacher. 　　
Good: I don’t think he likes the English teacher. 
D.  主句一般过去时态，从句也要用过去时态。
False: He wanted to know why he is crying in the corner. 　　
Right: He wanted to know why he was crying in the corner

宾语从句的否定转移:
主句的谓语动词是think,believe,imagine,suppose,consider,espect,fancy,guess等。
并且主句的主语是第一人称而且为一般现在时，从句的否定词一般要转移到主句上来,其反义疑问句一般与宾语从句一致。
I don’t think he will come to my party.而不能说成I think he won’t come to my party.
我认为他不会来我的舞会.
I don’t believe that man is killed by Jim,is he?
我认为那个人不是Jim所杀的,是不是?
如果宾语从句中有某个含有否定意义的形容词或副词,其反义疑问句要用肯定形式。
We find that he never listens to the teacher carefully,does he?
我们发现他从来不仔细听老师讲课，是不是?

宾语从句中引导词的用法比较
在复合句中作主句的宾语，引导词有：
连词：that (that 常可省略),whether, if
代词：who, whose, what ,which
副词：when ,where, how, why 等。

（一）that引导的宾语从句（在非正式场合that可以省略）
1.可跟that从句做宾语的动词有：
say, think, insist, wish, hope, demand, imagine, wonder, know, suppose, see, believe, agree, admit, deny, expect, explain, order, command, feel, dream, suggest, hear, mean, notice, prefer, request, require, propose, declare, report等。
例句：The boy believes that he will travel through space to other planets.
注意事项：当主句谓语动词是 think, believe, suppose, expect 等词，而宾语从句的意思是否定时，常把否定转移至主句表示。
例句：I don’t think it is right for him to treat you like that.

2.在以下情况中that不能省略
a.当句中的动词后接多于两个由that引导的宾语从句时，第一个that可省，但后面的that不可省。
例句：He said (that) you were too young to understand the matter and that he was asked not to tell you.
b.当主句的谓语动词与that宾语从句之间有插入语时，that一般不可省。
例句：Just then I noticed, for the first time, that our master was wearing his fine green coat and his black silk cap.
c.当that从句是双宾语中的直接宾语时，that不可省。
例句：I can’t tell him that his mother died.
d.注:许多带复合宾语的句子，that引导的宾语从句经常移到句子后部，而用it作形式宾语。
例句：I find it necessary that we should do the homework on time.

（二）由whether,if 引导的宾语从句
1.由whether(if)引导的宾语从句，实际上是一般疑问句演变而来的。意思是“是否”。宾语从句要用陈述句语序。
一般说来，在宾语从句中whether与if可以互换使用，但在特殊情况下if与whether是不能互换的。
例句：I wonder whether(if) they will come to our party.

2.只能用whether，不能用if引导的宾语从句
a.在带to的不定式前
例句：We decided whether to walk there.
b.在介词的后面
例句：I’m thinking of whether we should go to see the film.
c.在动词后面的宾语从句时
例句：We discussed whether we had a sports meeting next week
d.直接与or not连用时
例句：I can’t say whether or not thet can come on time.

3.只能用if不能用whether引导的宾语从句
a.if引导条件状语从句，意为“如果”
例句：The students will go on a picnic if it is sunny.
b.if引导否定概念的宾语从句时
例句：He asked if I didn’t come to school yesterday.
c.引导状语从句even if（即使）和as if（好象）时
例句：He talks as if he has known all about it.

if,whether在宾语从句中的区别
a.if和whether在作“是否”解时,引导宾语从句常放在动词know,ask,care,wonder,find out等之后,介词后一般不用if
b.少数动词,如:leave,put,discuss,doubt后的宾语从句常用whether. 
c. whether后可以加or not,但是if不可以.
d.在不定式前只能用whether.
（如：I can’t decide whether to stay. 我不能决定是否留下。）
e.避免歧异时,我们常用whether而不用if.

（三）连接代词和连接副词引导的宾语从句
这样的宾语从句实际上是由特殊疑问句变化而来的，宾语从句要用陈述句语序。
用于这种结构的动词常常是：see, say, tell, ask, answer, know, decide, show, find out, imagine, suggest, doubt, wonder, discover, understand, inform, advise等。
1.英语中的连接代词有：who,whom,whose,which,what,在句中担任主语、宾语、定语或者表语。
例句：Can you tell me whom you are waiting for?
2.英语中的连接副词有：when,where,why,how，在句中担任状语的成分。
例句：None of us knows where these new parts can be bought.

简化宾语从句常用六法：
方法一：
当主句谓语动词是hope， decide， wish， choose， agree， promise等，
且宾语从句的主语与主句主语一致时，宾语从句可简化为不定式结构。
例如：
Li Ming hopes he will be back very soon.
→Li Ming hopes to be back very soon.
We decided that we would help him.
→We decided to help him.

方法二：当主句谓语动词是know， learn， remember， forget， tell等动词，
且主句主语与从句主语一致时，宾语从句可简化为“疑问词+不定式”结构。例如：
She has forgotten how she can open the window.
→She has forgotten how to open the window.
注：当主句谓语动词是tell， ask， show， teach等动词，
且后带双宾语，从句主语和间接宾语一致时，宾语从句可简化为“疑问词+不定式”结构。例如：
Could you tell me how I can get to the station？
→Could you tell me how to get to the station？

方法三：当主句的谓语动词是order（命令），require（需要）等时，
如果主句和从句的主语不一致，宾语从句可简化为“名词（代词）+不定式”结构。例如：
The headmaster ordered that we should start at once.
→ The headmaster ordered us to start at once.

方法四：某些动词后的宾语从句，可以用介词加动名词（短语）等其他形式简化。例如：
He insisted that he should go with us.
→He insisted on going with us.
The poor boy doesn’t know when and where he was born.
→The poor boy doesn’t know the time and the place of his birth.

方法五：某些动词后面的宾语从句可转化为“宾语+V-ing形式（作宾语补足语）”结构。例如：
Liu Ping found that there was a wallet lying on the ground.
→ Liu Ping found a wallet lying on the ground.

方法六：动词seem后的宾语从句，也可以用不定式（短语）来简化，但句型需要进行适当的变化。例如：
It seemed that the boys were going to win.
→The boys seemed to win.
除上述方法外，还有一些特殊句式的转化。例如：
I found that it was difficult to learn English well.
→I found it difficult to learn English well.
Soon we found that the ground was covered with thick snow.
→Soon we found the ground covered with thick snow.
They found that the box was very heavy.
→They found the box very heavy