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連詞是一種在句子與句子之間，短語之間以及名詞等其他詞語之間起連接作用的虛詞，它不能單獨作句子的成份。按其意義可分為并列連詞和從屬連詞兩大類。

常有的并列連詞有

并列連詞連接的雙方是對等的。and, both…and, either…or, neither…nor， not only…but also, as well as等。但如果連接的兩部分意義不趨向一致，：but, however, yet, still，while等。

Mary was a nice girl, but she had one shortcoming.

Tomgot up early, yet he failed to catch the train.

He was very tired, still he kept on walking.

Your composition is fairly good, however, there is still some

room for improvement.

Jane is hard working ,while her sister is quite lazy.

還有表示選擇關系的并列連詞，

如：or, or else, otherwise… 再有的是連接雙方，互為因果，或表示前因后果的連詞有：for, so, therefore (因此)，then等。

從屬連詞在中學范圍內常常用來連接名詞性從句，

如：that, if, whether, 其次用來連接狀語從句。：when , while, as, since, before, after, once, as soon as, until, till。

連接條件狀語的連詞有：

if, unless, as long as 等，because, since, as, now that (既然)。so that, so…that, such…that, as…as, than, where… 它們在句子與文章中幾乎無處不見。

簡單連詞

并列連詞	用法	例句
and	表并列或順承關系	He came into the classroom and put his schoolbag on the desk.
and	用于“祈使句，and +陳述句”結構	Be careful, and you will make fewer mistakes.
or	意為“或者”，表示任選其一	Do you want to go the zoo or the museum?
or	意為“否則”，用于“祈使句，or +陳述句”結構	Please be quick, or we will miss the last bus.
so	表示因果關系	It’s raining heavily now, so we have to put off the P.E class.
for	表示原因，及附帶理由	I must be off now, for it is getting late.
but	“但是”，表轉折關系	Nearly every kid hates exams, but they’re necessary. They help to check if kids have learned the specific knowledge.

并列連詞短語

連詞短語	意義用法	例句
neither--nor-	既不--也不,謂語動詞的數遵循“就近原則”	Neither he nor his children like fish.
either--or--	或者--或者--，謂語動詞的數遵循“就近原則”	Either you or he is wrong.
both--and--	兩者都，謂語動詞用復數形式	Both she and I are good at English.
not only-- but also	不但--而且-，謂語動詞的數遵循“就近原則”	Not only you but also he wants to buy the book.

注意：

neither...nor, either...or, not only...but also連接兩個成分作主語時，謂語動詞要和最近的主語保持一致，即就近原則;both...and連接兩個成分作主語時，謂語動詞只能用復數。

1.引導時間狀語從句的從屬連詞

從屬連詞	用法	例句
when 當--時候	引導的從句中，謂語動詞可以是短暫性動詞也可以是延續性動詞	It was raining when he came out of the office.
while 當--時候	引導的從句中，謂語動詞必須是延續性動詞，且常用進行時	Don't make any noise while others are reading in the library.
before 在--之前	“在……之前”，從句的動作通常發生在主句動作之后	She reached the train station before he called her yesterday.
after 在---之后	“在……之后”，從句的動作通常發生在主句動作之前	He turned off the light and went to bed after he cleaned the room.
until	常用在“not...until...”結構中，表示“直到……才……”	Nancy didn't appear until it was ten o'clock last night.
as 一邊--一邊	表示一件事情在發生，另一件事情也在同時發生	The students took notes as they listened to the radio in English class.
as soon as 一--就--	表示從句的動作一發生，主句的動作就隨之發生	I'll write a letter to you as soon as I get to America.
since 自從	從句常用一般過去時，主句用現在完成時	The girl who can speak English smoothly has lived in London since she was five years old.
once 一旦	表示從句動作一發生，主句的動作就隨之發生	Once they find people in trouble, they are eager to help them without payment.

2.引導條件狀語從句的從屬連詞

連詞	用法	例句
if 如果	主句用一般現在時，主句通常用一般將來時，即主將從現，但有時用主情從現或主祈從現。	1.If he has time tomorrow, he will come to the meeting. 2.None can succeed if he doesn’t work hard.
unless 除非，如果不	主句用一般現在時，主句通常用一般將來時，即主將從現，但有時用主情從現或主祈從現。。 unless可轉化成if--not結構。	1.He won’t finish the work unless he works hard. 2.If it doesn’t rain, go for a picnic.
as long as 只要	主句用一般現在時，主句通常用一般將來時，即主將從現。	You can take any book as long as you like.

3.引導讓步狀語從句的從屬連詞

連詞	含義	用法
though	雖然	引導讓步狀語從句時，這些詞不能與but連用。
although	盡管
even though(if)	即使

4. 引導原因狀語從句

連詞	意義	例句
because	表示造成某種情況的直接原因，語氣最強，常用來回答由why引導的問句，其從句的位置通常在主句的后面。	He has to leave because it is too late. 因為太晚了，他不得不走。
since	since語氣比as稍強，不表示直接的或根本的原因，而是一種已知的或非常顯然的理由，since引導的從句通常位于主句之前。	Since everyone is here, let’s start. 既然大家到齊了，我們就出發吧！
as	as是從屬連詞，表示原因時，語氣最弱，所說的原因比較明顯或是已知的事實，它引導的從句一般位于主句之前。	We all like her as she is kind. 我們都喜歡她，因為她善良。
for	是并列連詞,表明附加或推斷的理由,常用于口語中,意為“因為”。for連接的句子不用于句首,并列句之間可以用逗號分開。	Imustbeawayforaweek,forI'llgotoShanghai. 我要離開一個星期,因為我要去上海。

5.引導方式狀語從句的從屬連詞

連詞	意義	例句
as	按照--方式	She always does as her father tells her.
as if	似乎，好像	He walked around as if he was looking for something.

6.引導結果狀語從句的從屬連詞

連詞

意義

用法及例句

so --that

如此--以至于

so后跟形容詞副詞原形。(so--that--結構常與too--to結構轉化）。

She was so tired that she couldn’t go any farther.

ThatquestionissodifficultthatIcan'tworkitout.

→Thatquestionistoodifficultformetoworkout.

這個問題太難,我算不出來。

such --that

such后跟名詞或名詞性詞組。

It’s such a fine day that many people go to the park for fun.

so...that...可以與以下結構轉換：

A. 與too...to...結構的轉換

too...to...意為“太……以至于不能……”,與so...that...結構互換時,that從句中必須使用情態動詞can't(如果是過去時則用couldn't)。

如:

Hewassocleverthathecouldn'tmakesuchstupidmistakes.

→ Hewastooclevertomakesuchstupidmistakes.

他太聰明了,不會犯這么愚蠢的錯誤。

溫馨提示:如果主從句的主語不一致,改為同義句時,要用too...for sb. to...結構。

如:

ThatquestionissodifficultthatIcan'tworkitout.

→Thatquestionistoodifficultformetoworkout.

這個問題太難,我算不出來。

B. 與enoughtodo/notenoughtodo結構的轉換

a)與enough to do sth.結構的轉換。

enough to do sth.意為“……足夠做某事”,與so...that...結構轉換時,that從句中必須使用情態動詞can。

如:

Youaresohealthythatyoucangetbacktoschool.

→ Youarehealthyenoughtogetbacktoschool.

你身體健康,可以回學校去了。

b)與not...enough to do結構的轉換。

not...enough to do意為“沒到做某事的……”,與so...that...結構轉換時,that從句中必須使用含有否定意義的情態動詞。enough前面的形容詞是so...that...結構中so后面形容詞的反義詞。

如:

Theboyissoyoungthathecan'tdresshimself.

→Theboyisnotoldenoughtodresshimself.

這個孩子還沒到自己穿衣服的年齡。

Heissoimpatientthathecan'twait.

→ Heisnotpatientenoughtowait.

他沒有足夠的耐心等待。

7.引導目的狀語從句的從屬連詞

連詞	意義	用法
so that	以便于，為了	They sped up so that they could get there on time.
in order that	為了	They sped up so that they could get there on time.