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與主語，謂語與謂語，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，定語從句和狀語從句等。

（一）并列連詞：

并列連詞可用來連接詞與詞，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（因為），so（所以），while（而），when（這時）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

從屬連詞是指在復合句中引導從句的連結詞。常見的從屬連詞有：

引導時間狀語從句的：after, before, when, as, while, since, until, till, as soon as

引導原因狀語從句的：because, since, as

引導讓步狀語從句的：although, though, no matter（無論）, even if (though)

引導條件狀語從句的：if, unless, once, so (as) long as

引導結果狀語從句的：so … that …, such … that …

引導目的狀語從句的：so that …, in order that …

引導比較狀語從句的：as … as …, not so (as) … as …, … than …

引導方式狀語從句的：as if …

引導主語，賓語或表語從句的連詞主要有：that, whether, if三個。其中that 和whether間或還可以引起同位從句和狀語從句。

（三）某些用法比較特殊的從屬連詞用法區別

1、當while, when, as引導時間狀語從句時的區別：①while引導的狀語從句中動詞必須是持續性。謂語動詞多為進行時，或狀態動詞的一般時。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除可指一段時間外，還可用來指一點時間，等于 “at the time”，也就是說when引出的時間狀語從句中的謂語動詞可以是終止性的，也可以延續性的。因此主句和從句的謂語可以是一般時，進行時，或完成時。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，但強調“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引導的狀語從句中的主語與主句主語一致，主、謂是“主語+系動詞”結構時，這時主語和系動詞可以省略。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有時代替if，引導條件句，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我；Before I could get in a word he had measured me.我還沒來得及插話，他已經給我量好了尺寸。

3、till, until作為介詞式從屬連詞引導時間狀語短語或狀語從句，用于否定句時，結構為not …until (till)，主句謂語動詞延續與非延續皆可，意為“直到…才…”。用于肯定句時，只與延續性動詞連用，表示“到…為止”。例如：They played volleyball until (till) it got dark./ They didn’t talk（延續性動詞）until (till) the interpreter（譯員）came./ He didn’t go to bed（非延續性動詞）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只用于時間，以下句子是錯誤的：We walked till the edge of the forest.（要用as far as或to）。

4、because, since, as引導原因狀語時注意使用上的區別：①如果原因構成句子的最主要部分,一般用because ,因此because引導的從句往往放在句末。用why提問的句子，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引導的從句一般放在句子的開頭。例如：As you are tired, you had better rest./ Since everyone is here, now let’s begin.

5、although和though引導讓步狀語從句往往用法一樣，但注意以下區別：①although用于各種文體，而though則多用于非正式的口語或書面語中。注意由although, though引導的從句后，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表示強調，意為“即使”，但不能說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”，常用逗號與句子分開。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”，作為連詞譯“一旦”，引導條件狀語從句。相當于if的加強形式。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引導條件狀語從句等于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引導的方式狀語從句及表語從句中，根據情況要使用虛擬語氣。例如：He talks as if he knew all about it. 但有時也可用直陳語氣。例如：It looks as if it is going to rain.

9、whether, if引導從句的用法區別：①引導主語從句、表語從句或同位語從句時，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可作介詞的賓語或置于句首表示強調，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均可引導賓語從句， whether引導的賓語從句一般都是肯定句，if引導的賓語從句可以是肯定的，也可以是否定的（此時不能用whether），例如：Could you tell us whether/ if it rains in winter in Australia?/ I wonder if it doesn’t rain. ⑤引導賓語從句的whether和if常可與or not連用。連用時要注意or not的位置，它一般與 whether、if分開使用，有時它可與whether合起來使用，但不能與if合起來使用。例如：I don’t know whether/ if they will come or not./ I don’t know whether or not they will come.　⑥if可用來引導條件狀語從句，譯“如果”，whether則不行。例如：If you work hard, you are sure to succeed.

10、as作從屬連詞可引導多種狀語從句。①as引導時間狀語從句，意為“當…時”。例如：As (he was) a young man, he was a storekeeper and later a postmaster./ He sang as he worked. ②as引導方式狀語從句，意為“象…一樣”。例如：We must do as the Party teaches us.　③as引導原因狀語從句。意為“由于”，例如：As you are tired, you had better rest.　④as引導讓步狀語從句。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做為關系代詞還可以引導定語從句，如：I have the same book as you.

練習、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