可分為兩類，一類是用于連接句子或從句，常見的有therefore, otherwise, however, moreover, still, thus, meanwhile等；
另一類是用于引導(dǎo)從句或不定式，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.
連接副詞的特點(diǎn)：
一、連接句子或從句的連接副詞
連接副詞的性質(zhì)類似于并列連詞，使用時(shí)其前通常用分號(hào)或句號(hào)；
若其前用逗號(hào)，則通常帶有并列連詞(如and)。如：
I don't like it; besides, it's too expensive. 我不喜歡它，而且也太貴了。
We all tried our best; however, we lost the game. / We all tried our best. However, we lost the game. 我們都已盡了最大的努力，不過我們還是輸了。
注意，有的連接副詞(如however等)后通常有逗號(hào)與句子的其他成分隔開。另外，有的這類副詞還可位于句中或句末：
Peter is our youngest child, and we have three others besides. 彼昨是我們最小的孩子，我們另外還有三個(gè)孩子。
He may, however, come later. 不過，他也許一會(huì)兒就到。
We all tried out best. We lost the game, however. 我們都已盡了最大的努力，不過我們還是輸了。
二、引導(dǎo)從句和不定式的連接副詞
用于引導(dǎo)從句(名詞性從句)或不定式的連接副詞主要有when, why, where, how等。如：
Tell me when we shall leave. / Tell me when to leave. 告訴我什么時(shí)候離開。
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. 到哪里去弄到這筆錢正是我們頭痛的事。
That's why he speaks English so well. 那就是他為什么英語講得這么好的原因。
注：連接副詞why 后不能不定式，如可說 I don't know why I must leave.(我不知道我為什么必須離開)，但不能說 I don't know why to leave。
連接副詞的句法特征：
所謂連接代詞和副詞，實(shí)際上就是我們以前學(xué)過的疑問代詞和副詞，如who, whose, whom, what, which, when,where, why,how以及由how構(gòu)成的詞組。
1.連接副詞起對(duì)等連接詞的作用,連接兩個(gè)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.我有點(diǎn)累了,但我能堅(jiān)持下去。
They talked about it for hours. Finally, they decided to go。他們對(duì)此商量了好幾個(gè)小時(shí),最后他們決定去。
2.連接副詞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。他們對(duì)此商量了好幾個(gè)小時(shí),最后他們決定去。
finally作為連接副詞,放在句子的句首。
I have never been to Wales. I, therefore, don't know much about it.我從未去過威爾斯,因此我對(duì)它知道的不多。
therefore作為連接副詞,位于句子的句中。
3.有些連接副詞的含義彼此相同或相近,在使用時(shí)可以互相替換,而不會(huì)改變?cè)涞暮x。
The weather was cold. Therefore(Thus), we stayed home.天氣寒冷,因此我們待在家里。
therefore和thus的含義相近,因而也可以互相替換。
在應(yīng)用時(shí)要注意以下兩點(diǎn)：
一是它們?cè)跇?gòu)成疑問句時(shí)叫疑問詞，引導(dǎo)賓語從句時(shí)稱作引導(dǎo)詞。
一是它們和that不一樣，在從句中有含義，擔(dān)任相關(guān)的句子成分，所以不能省略，另外，它們須放在賓語從句之首，賓語從句必須是陳述句結(jié)構(gòu)。
引導(dǎo)名詞性從句的連接詞可分為三類：
連接詞：that, whether, if, as if, as though（不充當(dāng)從句的任何成分，但絕不能省略）
連接代詞：what, whatever, who, whoever, whom, whomever, whose, which, whichever.
連接副詞：when, whenever, where, wherever, how, however, why
不可省略的連詞：
1. 介詞后的連詞
2. 引導(dǎo)主語從句和同位語從句的連詞不可省略。
That she was chosen made us very happy.
We heard the news that our team had won.
大部分連接詞引導(dǎo)的主語從句都可以置于句末，用 it充當(dāng)形式主語。
It is not important who will go.
It is still unknown which team will win the match.
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