連詞分為并列連詞和從屬連詞兩大類。并列連詞是連接主語(yǔ)與主語(yǔ)，謂語(yǔ)與謂語(yǔ)，句子與句子，分詞與分詞的詞，它要求前后兩部分有相同的形式和語(yǔ)法作用；而從屬連詞一般連接主句與從句，從句形式有名詞性從句，定語(yǔ)從句和狀語(yǔ)從句等。
（一）并列連詞：
并列連詞可用來(lái)連接詞與詞，詞組與詞組，分句與分句。常用的并列連詞有：and（和），as well as（既…又），both … and（不但…而且），not only … but also（不但…而且），not … but（不是…而是），neither … nor（既不…也不），either … or（不是…就是），or（或者），but （但是），yet（然而），for（因?yàn)椋瑂o（所以），while（而），when（這時(shí)）等。如：Both my brother and my sister are teachers./ His room is bright but mine is gloomy（暗沉沉的）./ He can not only repair radios but also fix them./ It is a glorious（光榮的）yet difficult task./ Strike while iron is hot.
（二）從屬連詞
從屬連詞是指在復(fù)合句中引導(dǎo)從句的連結(jié)詞。常見(jiàn)的從屬連詞有：
引導(dǎo)時(shí)間狀語(yǔ)從句的：after, before, when, as, while, since, until, till, as soon as
引導(dǎo)原因狀語(yǔ)從句的：because, since, as
引導(dǎo)讓步狀語(yǔ)從句的：although, though, no matter（無(wú)論）, even if (though)
引導(dǎo)條件狀語(yǔ)從句的：if, unless, once, so (as) long as
引導(dǎo)結(jié)果狀語(yǔ)從句的：so … that …, such … that …
引導(dǎo)目的狀語(yǔ)從句的：so that …, in order that …
引導(dǎo)比較狀語(yǔ)從句的：as … as …, not so (as) … as …, … than …
引導(dǎo)方式狀語(yǔ)從句的：as if …
引導(dǎo)主語(yǔ)，賓語(yǔ)或表語(yǔ)從句的連詞主要有：that, whether, if三個(gè)。其中that 和whether間或還可以引起同位從句和狀語(yǔ)從句。
（三）某些用法比較特殊的從屬連詞用法區(qū)別
1、當(dāng)while, when, as引導(dǎo)時(shí)間狀語(yǔ)從句時(shí)的區(qū)別：①while引導(dǎo)的狀語(yǔ)從句中動(dòng)詞必須是持續(xù)性。謂語(yǔ)動(dòng)詞多為進(jìn)行時(shí)，或狀態(tài)動(dòng)詞的一般時(shí)。while 的這些用法可用when代替，等于 “at the time that”, “during the time that”。例如：Please keep quiet while (when) others are studying；② when除可指一段時(shí)間外，還可用來(lái)指一點(diǎn)時(shí)間，等于 “at the time”，也就是說(shuō)when引出的時(shí)間狀語(yǔ)從句中的謂語(yǔ)動(dòng)詞可以是終止性的，也可以延續(xù)性的。因此主句和從句的謂語(yǔ)可以是一般時(shí)，進(jìn)行時(shí)，或完成時(shí)。例如：When I went into the lab, the teacher was doing an experiment.（when不能換成while）He often makes mistakes when he is speaking English.（when可換成while）③as常可與when，while通用，但強(qiáng)調(diào)“一邊、一邊”。例如：As (when, while) I was walking down the street, I noticed a police car in front of number 37. ④when引導(dǎo)的狀語(yǔ)從句中的主語(yǔ)與主句主語(yǔ)一致，主、謂是“主語(yǔ)+系動(dòng)詞”結(jié)構(gòu)時(shí)，這時(shí)主語(yǔ)和系動(dòng)詞可以省略。例如：When (he was) young, he worked for a rich man./ She’ll be here to give you help when (if it is) necessary. ⑤when有時(shí)代替if，引導(dǎo)條件句，意為“如果”、“假如”，例如：I’ll come when (if) I’m free.
2、before作連詞一般表示時(shí)間，意為“在…之前”，但有些句子中這樣譯就顯得別扭。試看以下句子的翻譯：He almost knocked me down before he saw me.他幾乎把我撞倒才看見(jiàn)我；Before I could get in a word he had measured me.我還沒(méi)來(lái)得及插話，他已經(jīng)給我量好了尺寸。
3、till, until作為介詞式從屬連詞引導(dǎo)時(shí)間狀語(yǔ)短語(yǔ)或狀語(yǔ)從句，用于否定句時(shí)，結(jié)構(gòu)為not …until (till)，主句謂語(yǔ)動(dòng)詞延續(xù)與非延續(xù)皆可，意為“直到…才…”。用于肯定句時(shí)，只與延續(xù)性動(dòng)詞連用，表示“到…為止”。例如：They played volleyball until (till) it got dark./ They didn’t talk（延續(xù)性動(dòng)詞）until (till) the interpreter（譯員）came./ He didn’t go to bed（非延續(xù)性動(dòng)詞）until (till) the his father came back.；until可以放在句首，till則不行，例如：Until the last minute of the match we kept on playing./ Not until he finished his work did he go home.（倒裝）；till, until只用于時(shí)間，以下句子是錯(cuò)誤的：We walked till the edge of the forest.（要用as far as或to）。
4、because, since, as引導(dǎo)原因狀語(yǔ)時(shí)注意使用上的區(qū)別：①如果原因構(gòu)成句子的最主要部分,一般用because ,因此because引導(dǎo)的從句往往放在句末。用why提問(wèn)的句子，一定用because回答。例如：He had to stay at home yesterday because he was ill.；②如原因已為人們所知，或不如句子的其他部分重要，就用as，或 since。since比as更正式些。as和since引導(dǎo)的從句一般放在句子的開(kāi)頭。例如：As you are tired, you had better rest./ Since everyone is here, now let’s begin.
5、although和though引導(dǎo)讓步狀語(yǔ)從句往往用法一樣，但注意以下區(qū)別：①although用于各種文體，而though則多用于非正式的口語(yǔ)或書(shū)面語(yǔ)中。注意由although, though引導(dǎo)的從句后，主句不能用but，但可用副詞yet, still。例如：Although/ Though it rained all the morning, they still went on working.（或yet they went on working）②though常與even連用，even though表示強(qiáng)調(diào)，意為“即使”，但不能說(shuō)even although，例如：Even though I didn’t understand a word, I dept smiling. ③though可用作副詞，意為“然而”，常用逗號(hào)與句子分開(kāi)。although則不能這樣使用，它只作連詞。例如：It was a quiet party, I had a good time, though.
6、once作副詞譯“曾經(jīng)”，作為連詞譯“一旦”，引導(dǎo)條件狀語(yǔ)從句。相當(dāng)于if的加強(qiáng)形式。例如：I don’t believe he was once a thief. (once這里是副詞)/ Once Aristotle had made up his mind that heavy objects always fell faster than light objects, he taught it as a truth to his students. (once連詞)
7、unless引導(dǎo)條件狀語(yǔ)從句等于if … not …。例如：He’ll accept the job unless the salary is too low. ( = He’ll accept the job if the salary is not too low.)
8、在用as if引導(dǎo)的方式狀語(yǔ)從句及表語(yǔ)從句中，根據(jù)情況要使用虛擬語(yǔ)氣。例如：He talks as if he knew all about it. 但有時(shí)也可用直陳語(yǔ)氣。例如：It looks as if it is going to rain.
9、whether, if引導(dǎo)從句的用法區(qū)別：①引導(dǎo)主語(yǔ)從句、表語(yǔ)從句或同位語(yǔ)從句時(shí)，用whether，不用if。例如：Whether they will go to the Great Wall is not known./ The question is whether we can finish the task on time./ The question whether we will take part in the physics contest has not been decided. ②whether可接不定式，而if則不可。例如：I haven’t decided whether to leave or not. ③whether可作介詞的賓語(yǔ)或置于句首表示強(qiáng)調(diào)，而if則不可。例如：Everything depends on whether we have enough money./ Whether he will come, I am not sure. ④whether和if均可引導(dǎo)賓語(yǔ)從句， whether引導(dǎo)的賓語(yǔ)從句一般都是肯定句，if引導(dǎo)的賓語(yǔ)從句可以是肯定的，也可以是否定的（此時(shí)不能用whether），例如：Could you tell us whether/ if it rains in winter in Australia?/ I wonder if it doesn’t rain. ⑤引導(dǎo)賓語(yǔ)從句的whether和if常可與or not連用。連用時(shí)要注意or not的位置，它一般與 whether、if分開(kāi)使用，有時(shí)它可與whether合起來(lái)使用，但不能與if合起來(lái)使用。例如：I don’t know whether/ if they will come or not./ I don’t know whether or not they will come. ⑥if可用來(lái)引導(dǎo)條件狀語(yǔ)從句，譯“如果”，whether則不行。例如：If you work hard, you are sure to succeed.
10、as作從屬連詞可引導(dǎo)多種狀語(yǔ)從句。①as引導(dǎo)時(shí)間狀語(yǔ)從句，意為“當(dāng)…時(shí)”。例如：As (he was) a young man, he was a storekeeper and later a postmaster./ He sang as he worked. ②as引導(dǎo)方式狀語(yǔ)從句，意為“象…一樣”。例如：We must do as the Party teaches us. ③as引導(dǎo)原因狀語(yǔ)從句。意為“由于”，例如：As you are tired, you had better rest. ④as引導(dǎo)讓步狀語(yǔ)從句。意為“雖然”、“盡管”Child as he is, he can do it well. ( = Although he is a child, he can do it well.) 另外，as做為關(guān)系代詞還可以引導(dǎo)定語(yǔ)從句，如：I have the same book as you.
練習(xí)、連詞
1 .He is very old,____ he still works very hard. A. but B.if C.when D.as
2. ____ you are dismissed.
A. Neither you go nor B. Either you go or C. Whether you go or D. Both you go and
3. They had camped once before, ____ they knew what to take.
A. because B. now C. so D. since
4. Why these things happened was ____ the driver had been careless.
A. because of B. owing to C. due to D. that
5. Although, it's raining, ____are still working in the fields.
A. they B. but they C. and they D. so they
6.___we have satisfied you, you have no grounds of complaint.
A. So B. Since that C. Now that D. By now.
7. Write clearly ____ your teacher can understand .you correctly.
A. since B. for C. because D. so that
8.You'll miss the train ____ you hurry up. A. unless B. as C. if D. until
9. Francis did the task____ his brother. A. as good as B. as better as C. as well as D. as best as
10.The size of the audience,____ we had expected, was well over twenty thousand.
A. as B. what C. that D. whom
11.I thought he hated the TV .You are right,____ he still watches the program.
A. yet B. besides C. also D. then
12. It looks ____ it's going to rain. A. that B. as C. as if D. like that
13.____ to New York, her father has not heard from her.
A. Because she went B. After she went C. When she went D. Since she went
14.___he daydreamed, Peter saw figures in the sky. A. Until B. Since C. While D. During
15. We arrived at the station ____ the train had left. A. after B. before C. since D. when
16.____ he was in poor health, he worked just as hard as everyone else.
A. But B. Although C. Even if D. If
17. Give me one more minute ____ I'll have finished. A. so B. until C. and D. when
18. The worker hunted for jobs in New York for months,____ he could not find any work.
A. and B. yet C. or D. and but
19. Hurry up, ____ you'll be late. A. or B. and C. so D. yet
20. Do not make the same mistake ____ I did. A. so B. as C. like D. that
21. My sister is expecting me,____ I must be off now. A. however B. or C. so D. otherwise
22. We should pay attention ____ to industry ____ to agriculture.
A. either, or B. neither, nor C. not, but D. both, and
23. He ran off____ I could stop him. A. before B. after C. since D. when
24.____ you told me, I had heard nothing of what happened. A. Till B. Until C. After D. Since
25. Where have you been ____ you left home? A. before B. as C. since D. when
26.____ the problem of method is solved, talking about the task is useless.
A. Until B. Since C. After D. Unless
27. We have produced 15% more cotton this year____ we did last year.
A. as B. than C. like D. white
28.It is late; ____, I'm too tired to go out. A. besides B. except C. except for D. except that
29. Everything around us is ____ solid ..liquid ____ gas.
A. not .. .but... B. either.. .or... C. neither.. .nor... D. whether.. .or...
30. He will come ____ you ask him. A. whether B. unless C. if D. while
31.____ he will come or not is still unknown. A. If B. Where C. That D. Whether
32.I don' t know ____ to stay at home or go out. A. whether B. if C. how D. where
33. He spoke loudly ____ the audience could hear him clearly.
A. so B. that C. so that D. in order to
34. The book is not easy.____ it's rather difficult.
A. On the one hand B. On the contrary
C. On the other hand D. On the other contrary
35. You must work hard,____ you will not learn English well.
A. if B. whether C. otherwise D. unless
36. It rained heavily,____ the basketball match had to be put off.
A. so that B. when C. otherwise D. therefore
37. We must do ____ the people want us to do..
A. whatever B. however C. wherever D. whenever
38. You are certainly right,____ others may say. A. what B. whatever C. that D. as
39.____ makes mistakes must correct them. A. Who B. What C. Whoever D. Whatever
40.I’ll discuss it with you ____ you like to come.
A. when B. where C. whoever D. whenever
41.____ you work, you must always serve the people heart and soul.
A. Wherever B. Whenever C. Where D. When
42.___you understand this rule, you will have no further difficulty.
A. Once B. At once C. Only D. Only then
43.___ difficult the task may be, we must fulfil it this month.
A. No matter how B. No matter what C. No matter when D. No matter where
44. We can surely overcome these difficulties _,___ we are closely united.
A. so far as B. so long as C. as soon as D. as well as
45.___ I know he will stay here for half a year.
A. as soon as B. as long as C. so far as D. as well as
46. Please write me ____ you arrive in New York.
A. as well as B. so long as C. as far as D. as soon as
47. That is not ____ I want. A. that B. why C. what D. whose
48. ___ he did it remains a secret. A. What B. Whom C. Which D. How
49. It is quite clear ____ he won't see us. A. what B. that C. why D. how
50. Would you tell me ____ way I should take? A. what B. that C. which D. whose
51. I am sure ____ you said is true. A. what B. that C. which D. who
52. The trouble is ____ we can not find such an expert.
A. why B. that C. where D. /
53. It has not been decided ____ they will leave.
A. why B. when C. which D. what
54. We shall go ____ you are ready. A. while B. as soon as C. as D. since
55. He will tell you about it ____ you get there. A. while B. as C. when D. /
56. Don't try to get off the bus ____ it has stopped.
A. while B. as C. since D. before
57. I'll come and see you _____ I go to the countryside.
A. while B. when . C. as soon as D. before
58. ___ he came to study in the university, he has made much progress in the study of English.
A. While B. When C. Since D. After
59. Things have changed a lot ____ I wrote to you last time.
A. when B. since C. as D. before
60. I can't use your pen, ___ there is no ink in it. A. for B. when C. if D. whether
61. I'd like to go swimming ____ the water is not too cold.
A. for B. unless C. if D. whether
62. Difficulties are nothing ___ we are not afraid of them.
A. for B. as C. if D. whether
63. The doctor will not perform the operation ___ it is absolutely necessary.
A. when B. if C. for D. unless
64. Go back ___ you came from. A. until B. where C. which D. when
65. He lay ___ the grass was the thickest. A. where B. when C. that D. after
66. You will find friendly people ___ you go in China.
A. where B. and C. wherever D. so
67. ___ it was already dark, they went on working in the fields.
A. If B. Whether C. But D. Though
68. ___ he has finished writing the novel is unknown.
A. If B. Whether C. When D. While
69. We'll go and see the patient ___we are busy.
A. even if B. for C. if D. while
70. The museum is ___ far ____ it will take us half an hour to get there by bus.
A. such... that B. as...as C. so...that D. so … as