if引导的条件句的用法

1、1if引导的条件句的用法1）当if用于表示普遍真理和科学事实的条件句中，其主从句的谓语动词一 般都用一般现在时。If you hea t ice, it mel ts.如果给冰加热，冰便融化了。If you pour oil on water, it floats.把油倒在水上，油浮于水面。If the temperature drops to zero degrees centigrade, water freezes.如果温度降至零度，水便结冰了。If you divide eight by two, you get four.8除以2，等于4。2）当if用于表示现在习惯动作条件句中，其主

2、从句的谓语也都用一般现在 时。lf I make a promise, I keep it.我只要许下诺言，就信守不渝。if it rains, I go to work by bus.每逢雨天，我就搭乘公共汽车上班。3）当if用于表示过去习惯动作的条件句中，其主从句谓语动词都用一般过 去式。lf I made promise, I kept it. 以前我只要许下诺言，就总是信守不渝。If it rained, I went to work by bus. 以前每逢下雨，我就坐公共汽车上班。4）if还常与从句一般现在时，主句用will/shall/can加动词原形结构搭配 使用。If you

3、 go to England, you will have to learn English .如果你到英国去，就必须学英语。If it is fine tomorrow , we can have a picnic somewhere .如果明天晴天，我们可以去野餐。if从句还常出现以下结构，主句祈使句，从句一般现在时。If you wake up before me, give me a call.如果你比我醒得早，就叫醒我。If you meet Mary in London , introduce youself to her .如果你在伦敦遇见玛丽，就向她做自我介绍。有时if从句中还

4、使用“should+动词原形”结构，加重语气。If we should miss the 10 oclock t rain, we wont get t here till after lunch.如果我们错过10点钟的火车，就要在午餐后才能到达。If he should fail to come, ask Philip to work in his place.万一他不来，就请菲利浦代替他工作。if从句中也常使用“will+动词原形”结构，表示“意愿”。If he will accept the nomination , a lot of electors will vote for him

5、 .如果他愿意接受提名，许多选民都会投他的票。lf you will wait for a few more minutes, the doctor will see you without your making an appointment.如果你愿意再等几分钟，医生不用预约就来看你。if主从句中都用“would+动词原形”结构，表示“意愿”，用于客气的 请求。If you would try Italian food, you would like it.如果您愿意尝试意大利食品，你会喜欢的。If you would read more carefully , you would und

6、erstand what the writer is trying to say.如果你愿意更加细心阅读，你会理解作家的意图。2If you offered me six times what you have just offered, I would still take my pound of flesh. 即使你愿意给我六倍于你刚才提出的钱数， 我仍然要拿我应得的那一磅肉。引导从句的连词if二even if,作“即使”解，引导的是让步状语从句，此 句中的谓语动词用了虚拟语气。例如：If I am mis taken, you are mis taken, too.就算我错了，你也错了。If he did say that, Im sure he didnt intend to hurt your feelings.就算