英语语法条件句

1、条件句一、条件句概说条件句指某一事情发生之后其它事情才发生。if通常的意思是“假如”，其后有时跟then。如果没有，一般也隐含在内。例如：If X happens, (then) Y follows.二、条件句的类型（一）零条件句1. 常用结构从句主句If you heat ice,it turns to water. If you lower the temperature of water to 0, it freezes.If there is a shortage of any product, the price of that product goes up. 2. 什么时候使用零

2、条件句如果我们谈论的事情总是正确的，比如科学事实、客观真理等，则使用这一类条件句。（二）第一条件句（真实）1. 常用结构从句主句if + 现在时Will 将来时eg. If it rains,we will stay at home.2. 什么时候使用第一类条件句如果我们认为将来发生的事情是可能发生的，就用第一类条件句，描述将会发生什么事情或不会发生什么事情。具备的条件可能的结果If it rains, we wont go for a picnic.If it doesnt rain,we will go for a picnic.PS: 具备的条件是真实的，天气可能下雨，可能不下雨。如果是

3、这样，它就会有真实的结果。所以，这样的句子被称为“开放”条件句或“真实”条件句。3. 第一类条件句变体I：If从句需具备的条件情态动词表示可能的结果phone me.一般现在时If she arrives early,she can/ could/ may/ might/ should/ ought to/ must现在进行时If she is arriving today,现在完成时If she has arrived, 现在完成进行时If she has been waiting, can, must If she cant understand4. 第一类条件句变体II：if 从句具备的

4、条件（不确定性增加）主句：祈使句If you (should) visit me,please let me know. Should you visit me,5. 第一类条件句变体III：祈使句+连词+小句祈使句具备的条件连词小句Stop crying,and I will give you an ice-cream.Drop the gun, or (otherwise)I will kill you.（三）第二条件句（非真实）1. 常用结构从句：if + 一般过去时主句 would/ could等情态动词If you got up early, you would catch the

5、train.If you didnt stay up late last night, you wouldnt feel so sleepy this morning. PS：尽管if从句用过去时，但并非指过去的时间，而是对现在情况的否定，因此也称为“非真实的过去”。2. 什么时候使用第二条件句if谈论的是对现在情况的否定，主句推测想象的结果。3. 第二条件句的变体从句主句If I / he/ she/ it were/waswould, could, should, might, could, might do you/ we they wereeg. If I were in your p

6、osition, I would accept their offer. If I were Jack, I would help Jane. Were I Jack, I would help Jane. （四）第三条件句（非真实）1. 常用结构if 从句：过去完成时主句：would/ could have done.If I had taken your advice, I would have met John. If we had gone by train, we would have been arrived earlier. If I had been trying harder, I would have succeeded. If I hadnt been wearing a raincoat, I would have got wet. 2. 什么时候使用第三条件句if从句是纯粹想象的事情，与现在事实相反，主句则是讲述想象的结果。3. 第三条件句的变体：had倒装从句主句Had we gone by train, we would have been arrived e