1、 條件狀語(yǔ)從句條件狀語(yǔ)從句在復(fù)合句中表示主句動(dòng)作發(fā)生的條件。一.if 引導(dǎo)的條件狀語(yǔ)從句1.用法條件狀語(yǔ)從句最常用的引導(dǎo)詞是if ,意為“如果，假如”，表示在某種條件下某事很可能發(fā)生。If it doesnt rain tomorrow ,we will go hiking .You will get good grades if you study hard.if 引導(dǎo)的條件狀語(yǔ)從句可以位于主句之前，也可以位于主句之后。如果從句在前，和主句之間要用逗號(hào)隔開(kāi)。2.時(shí)態(tài)(1)表示將來(lái)可能發(fā)生的事情；主句：常用一般將來(lái)時(shí)。從句：用一般現(xiàn)在時(shí)。(主將從現(xiàn))If you ask him, he wil

2、l help you.If he doesnt study hard, he will not pass the exam.If it doesnt rain tomorrow, we will go hiking.They are going to have a picnic if they are free next Saturday.(2)主句可含有情態(tài)動(dòng)詞或一個(gè)祈使句。從句：用一般現(xiàn)在時(shí)。If it stops snowing, we can go out.Dont wait for me if Im late .（3表示與現(xiàn)在事實(shí)相反的情況，主句：would/should/could

3、/might+動(dòng)詞原形。從句：一般過(guò)去時(shí),be動(dòng)詞常用were.If I had his telephone number, I would call him now.If I were you, I would not tell him that thing.二.unless引導(dǎo)的條件狀語(yǔ)從句。1.用法條件狀語(yǔ)從句也可由unless來(lái)引導(dǎo)，它的意思是“除非，如果不”，表示某件事只在特定情形下才會(huì)發(fā)生或成立。Unless you study hard, you will never pass the exam.You will be late unless you go at once.2.時(shí)

4、態(tài)(1)主句：常用一般將來(lái)時(shí)。從句：用一般現(xiàn)在時(shí)。(主將從現(xiàn))Unless it rains, the game will be played.You wont know the answer unless you listen carefully.(2)主句：可含有情態(tài)動(dòng)詞或一個(gè)祈使句。從句：用一般現(xiàn)在時(shí)。He cant see clearly unless he wears glasses.You must stop if the traffic light is red.If you drive too fast, you may have an accident. Dont make

5、any promise unless you can keep it. Dont touch the machine unless the teacher allows you to. Dont watch TV if you dont finish your homework.注：在“祈使句+and/or+陳述句”結(jié)構(gòu)中，祈使句在意義上相當(dāng)于條件狀語(yǔ)從句，二者可以相互轉(zhuǎn)換。Use your head, and youll find a way. = If you use your head, youll find a way.you wont know the answer if you d

6、ont listen carefully.=You wont know the answer unless you listen carefully.= Listen carefully, or you wont know the answer.三.unless與if.not 的區(qū)別。(1)if.not 與 unless 一樣，也表示“除非.,如果不.”,在很多情況下，二者可以互換使用。I wont go to the party if Im not invited .= I wont go to the party unless Im invited. If it doesnt rain t

7、omorrow, we will go hiking.=We will go hiking unless it rains tomorrow.She will keep on singing if she is not told to stop.=She will keep on singing unless she is told to stop.(2)當(dāng)某種條件所引起的結(jié)果是一種情緒或想法時(shí)，只能用if.not ,不用unless .I will be happyifIdonthave to do the homework.()I will be happyunless Ihave to

8、do the homework. ()I will be angryifI amnotinvited to the party. ()I will be angryunlessI am invited to the party. ()(3)當(dāng)表示與現(xiàn)在事實(shí)相反的情況時(shí)，只能用if.not,不用unless. 主句：would/should/could/might+動(dòng)詞原形。從句：一般過(guò)去時(shí),be動(dòng)詞常用were.Ifyouwerentalways in such a hurry ,your work would be much better.()Your work would be much better unless you w