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英语中的if条件句由两部分组成,一个是连词if引导的条件状语从句,一个是表示结果的主句,if从句可置于主句之前或之后。主从句的谓语动词的时态形式取决于说话者认为结果是否是真实的。if条件句分为零条件句、第一条件句、第二条件句和第三条件句四种,见下表(The 4 Types of Conditionals):
下面以动词do为例分别讲解if引导的四种条件状语从句。
一、零条件句/绝对真实条件句(Zero Conditional)
零条件句,又叫绝对真实条件句,用于阐述事实。用来表达在该条件下,结果一定会如此(如规则,客观规律、真理等)。结构是:If+主语+do/does,主语+do/does。其从句和主句的谓语动词通常为一般现在时。如:
If ice is heated,it melts.如果冰被加热,就融化了。(表示科学理论的条件句)
If you heat water,it boils. 如果你烧水,水会开。(表示科学理论的条件句)
If the temperature drops to 0 ℃,water freezes. 如果温度降至零摄氏度,水就会结冰。(表示科学理论的条件句)
If I am late for training,my coach gets angry. 如果我培训迟到了,我的教练会很生气。(表示客观事实的条件句)
Im happy to go to the party if you come with me.如果你和我一起,我就愿意去参加晚会。(意思是你去我才去)(表示客观事实的条件句)
In time of serious accidents,if we know some basic things about first aid,we can save lives. 在严重事故的时候,如果我们了解一些基本的急救常识,我们可以挽救生命.(表示客观事实的条件句)
If I felt any doubt,I always asked my teachers. 我一有了疑惑,总要问我的老师。(表示现在习惯动作,其从句和主句谓语动词为一般现在时;如表示过去习惯动作,其从句和主句谓语动词为一般过去时。)
请注意,在零条件句(即绝对真实条件句)里,主句和从句都使用现在时态,而且连词if相当于when。
【例题】 neighbors want to get along well with each other,they have to show their tolerance.
【答案与解析】 If/When。本句可以用if也可以用when,主从句都是一般现在时,属于绝对真实条件句,if从句是表示客观事实的条件句,所以也可以用when。句意:如果邻居间想要友好相处,他们就必须表现出能够对他人容忍的一面。
【例题】 If steel is heavier than water,why are ships able to float on the sea?
【解读】 If steel is heavier than water是一个条件状语从句,疑问句why are ships able to float on the sea。句意:既然铁重于水,为什么船可以浮在水面上。
二、第一条件句/相对真实条件句(First Conditional)
第一条件句又叫相对真实条件句,谈论将来可能发生的事情,并考虑这件事情的结果。强调偶然性或一次性的条件,也可以与绝对真实条件句同义。if从句用一般现在时或其他现在时,表示将来可能发生的事情(条件);主句用一般将来时,表示这件事情的结果。结构是:If+主语+do/does,主语+will do。如:
I will tell him about it if he comes. 要是他来的话,我就把此事告诉他。
I will be happy to go to the party if you come with me. 如果你和我一起去的话,我就会很开心地去参加晚会。(也就是说你去不去,我都得去)
If you want to make your dream come true,the first thing you have to do is to wake up.
若要梦想实现,先要从梦中醒来。
You will get the full mark if you study hard. 如果你努力学习,你就会得满分。
If ice meets heat,it will melt. = If ice is heated,it melts.
【例题】 Thats why I help brighten peoples days.If you dont,whos to say that another person will?
【解读】 “主将从现”是指在条件状语从句和时间状语从句中,如果主句是一般将来时,从句用一般现在时替代一般将来时。本句主句是一般将来时,if条件状语从句用一般现在时代替将来。
【例题】 Peter:Unbelievable!Oh... , you dont mind,Ill stop and take a deep breath.
【答案与解析】 if 。句意:这真是难以相信,如果你不介意,我要停下了深呼吸一下。
三、第二条件句/现在虚拟条件句(Second Conditional)
第二条件句是虚拟条件句的一种,即现在虚拟条件句(Unreal Present),用来表达在现在或将来时间下不太可能或不可能发生的条件,这种条件句还可以用来表示试探性的、委婉的语气(可以理解为不大有自信,所以不太真实的条件)。结构是:①与将来事实相反的非真实条件句是If+主语+should do/were to do/did,主语+would/should/could/might do;②与现在事实相反的非真实条件句是If+主语+did,主语+would/should/could/might+do。如: If I should have/were to have / had enough money next month,I would buy a copy of “The Advanced Learners Dictionary of Current English”。如果我下个月有足够的钱,我就会买一本《现代高级英语学习词典》。
If I didnt suffer from a fear of flying,I would travel more. 我要不是晕机的话,我会多出行的。(现在实际情况是由于晕机出行较少)
If I were you,I would ask our teacher for advice. 如果我是你的话,我就请教老师。
If I wanted you to travel to Tibet with me,would you want to go?要是我让你跟我一起去西藏,你愿意去吗?(问话者问的比较委婉)
【例题】 This meeting room is a non-smoking area. I would like to warn you in advance that if you smoked here you would be fined.
【解读】 句意:这个会议室是无烟区域,我想提前警告你:如果你在这里吸烟,会被罚款。“if you smoked here you would be fined”是表示与将来情况相反的虚拟语气,表示在提前警告某人。
【例题】 If you are me,would you talk to him?
【答案与解析】 are—were。考查虚拟语气。根据句子可知,此处为虚拟语气,与现在事实不相符,故把are改成were。句意:如果你是我,你会跟他谈谈吗?
三、第三条件句/过去虚拟条件句(Third Conditional)
第三条件句是表示与过去事实相反的虚拟语气,是用来表达如果(If)当时那样发生,另外一方面(当时)结果会如何。通常是指过去的事情,带有一切已经太迟而不能够补救的意思。结构是:If+主语+had done,主语+would/should/could/ might+have done。如:
If she hadnt been ill,she would have gone to work. 当时她要不是生病就去上班了。(事实是生病了而没有去上班。)
If he hadnt been so lazy in college,he would have found a much better job when he graduated. 他要不是读大学时候那么懒,毕业的时候就找到一份更好的工作了。
If he had studied harder in college,he would have found a much better job when he graduated. 他读大学时候要是再努力点,毕业的时候就找到一份更好的工作了。
If the Second World War had not broken out,the Cold War might not have come to pass. 如果第二次世界大战没有发生,冷战也不一定会出现。
【例题】 If I (not see)it with my own eyes,I wouldnthave believed it.
【答案与解析】 hadnt seen。根据后半句wouldnt have believed可以判断是表示与过去事实相反的虚拟语气,所以从句是if+主语+had+done的形式。句意:如果不是我亲眼看到,我不会相信。
【即时演练】 翻译填空,注意if 从句的用法。
1. (如果你把一个鸡蛋丢下去),it breaks.
2. If you blow on a candle, (它就熄灭了).
3. If her mother (听从医生的建议),she would/might have got well earlier.
4. If I (没有搭错车),I wouldnt have missed the contest.
5. (如果你认为) treating a woman well means always getting her permission for things,think again.
6. (如果我是你),I would take an umbrella.
7. (如果没有水和空气),there would be no living things on the earth.
8. If (她下周一来这儿的话) next Monday,I would tell her about the matter.
Keys:1. If you drop an egg 2. it is out 3. had taken the doctors advice 4. hadnt taken the wrong bus 5. If you think (that) 6. If I were you 7. If there were no air or water 8. she were to be/ should be/ were there
下面以动词do为例分别讲解if引导的四种条件状语从句。
一、零条件句/绝对真实条件句(Zero Conditional)
零条件句,又叫绝对真实条件句,用于阐述事实。用来表达在该条件下,结果一定会如此(如规则,客观规律、真理等)。结构是:If+主语+do/does,主语+do/does。其从句和主句的谓语动词通常为一般现在时。如:
If ice is heated,it melts.如果冰被加热,就融化了。(表示科学理论的条件句)
If you heat water,it boils. 如果你烧水,水会开。(表示科学理论的条件句)
If the temperature drops to 0 ℃,water freezes. 如果温度降至零摄氏度,水就会结冰。(表示科学理论的条件句)
If I am late for training,my coach gets angry. 如果我培训迟到了,我的教练会很生气。(表示客观事实的条件句)
Im happy to go to the party if you come with me.如果你和我一起,我就愿意去参加晚会。(意思是你去我才去)(表示客观事实的条件句)
In time of serious accidents,if we know some basic things about first aid,we can save lives. 在严重事故的时候,如果我们了解一些基本的急救常识,我们可以挽救生命.(表示客观事实的条件句)
If I felt any doubt,I always asked my teachers. 我一有了疑惑,总要问我的老师。(表示现在习惯动作,其从句和主句谓语动词为一般现在时;如表示过去习惯动作,其从句和主句谓语动词为一般过去时。)
请注意,在零条件句(即绝对真实条件句)里,主句和从句都使用现在时态,而且连词if相当于when。
【例题】 neighbors want to get along well with each other,they have to show their tolerance.
【答案与解析】 If/When。本句可以用if也可以用when,主从句都是一般现在时,属于绝对真实条件句,if从句是表示客观事实的条件句,所以也可以用when。句意:如果邻居间想要友好相处,他们就必须表现出能够对他人容忍的一面。
【例题】 If steel is heavier than water,why are ships able to float on the sea?
【解读】 If steel is heavier than water是一个条件状语从句,疑问句why are ships able to float on the sea。句意:既然铁重于水,为什么船可以浮在水面上。
二、第一条件句/相对真实条件句(First Conditional)
第一条件句又叫相对真实条件句,谈论将来可能发生的事情,并考虑这件事情的结果。强调偶然性或一次性的条件,也可以与绝对真实条件句同义。if从句用一般现在时或其他现在时,表示将来可能发生的事情(条件);主句用一般将来时,表示这件事情的结果。结构是:If+主语+do/does,主语+will do。如:
I will tell him about it if he comes. 要是他来的话,我就把此事告诉他。
I will be happy to go to the party if you come with me. 如果你和我一起去的话,我就会很开心地去参加晚会。(也就是说你去不去,我都得去)
If you want to make your dream come true,the first thing you have to do is to wake up.
若要梦想实现,先要从梦中醒来。
You will get the full mark if you study hard. 如果你努力学习,你就会得满分。
If ice meets heat,it will melt. = If ice is heated,it melts.
【例题】 Thats why I help brighten peoples days.If you dont,whos to say that another person will?
【解读】 “主将从现”是指在条件状语从句和时间状语从句中,如果主句是一般将来时,从句用一般现在时替代一般将来时。本句主句是一般将来时,if条件状语从句用一般现在时代替将来。
【例题】 Peter:Unbelievable!Oh... , you dont mind,Ill stop and take a deep breath.
【答案与解析】 if 。句意:这真是难以相信,如果你不介意,我要停下了深呼吸一下。
三、第二条件句/现在虚拟条件句(Second Conditional)
第二条件句是虚拟条件句的一种,即现在虚拟条件句(Unreal Present),用来表达在现在或将来时间下不太可能或不可能发生的条件,这种条件句还可以用来表示试探性的、委婉的语气(可以理解为不大有自信,所以不太真实的条件)。结构是:①与将来事实相反的非真实条件句是If+主语+should do/were to do/did,主语+would/should/could/might do;②与现在事实相反的非真实条件句是If+主语+did,主语+would/should/could/might+do。如: If I should have/were to have / had enough money next month,I would buy a copy of “The Advanced Learners Dictionary of Current English”。如果我下个月有足够的钱,我就会买一本《现代高级英语学习词典》。
If I didnt suffer from a fear of flying,I would travel more. 我要不是晕机的话,我会多出行的。(现在实际情况是由于晕机出行较少)
If I were you,I would ask our teacher for advice. 如果我是你的话,我就请教老师。
If I wanted you to travel to Tibet with me,would you want to go?要是我让你跟我一起去西藏,你愿意去吗?(问话者问的比较委婉)
【例题】 This meeting room is a non-smoking area. I would like to warn you in advance that if you smoked here you would be fined.
【解读】 句意:这个会议室是无烟区域,我想提前警告你:如果你在这里吸烟,会被罚款。“if you smoked here you would be fined”是表示与将来情况相反的虚拟语气,表示在提前警告某人。
【例题】 If you are me,would you talk to him?
【答案与解析】 are—were。考查虚拟语气。根据句子可知,此处为虚拟语气,与现在事实不相符,故把are改成were。句意:如果你是我,你会跟他谈谈吗?
三、第三条件句/过去虚拟条件句(Third Conditional)
第三条件句是表示与过去事实相反的虚拟语气,是用来表达如果(If)当时那样发生,另外一方面(当时)结果会如何。通常是指过去的事情,带有一切已经太迟而不能够补救的意思。结构是:If+主语+had done,主语+would/should/could/ might+have done。如:
If she hadnt been ill,she would have gone to work. 当时她要不是生病就去上班了。(事实是生病了而没有去上班。)
If he hadnt been so lazy in college,he would have found a much better job when he graduated. 他要不是读大学时候那么懒,毕业的时候就找到一份更好的工作了。
If he had studied harder in college,he would have found a much better job when he graduated. 他读大学时候要是再努力点,毕业的时候就找到一份更好的工作了。
If the Second World War had not broken out,the Cold War might not have come to pass. 如果第二次世界大战没有发生,冷战也不一定会出现。
【例题】 If I (not see)it with my own eyes,I wouldnthave believed it.
【答案与解析】 hadnt seen。根据后半句wouldnt have believed可以判断是表示与过去事实相反的虚拟语气,所以从句是if+主语+had+done的形式。句意:如果不是我亲眼看到,我不会相信。
【即时演练】 翻译填空,注意if 从句的用法。
1. (如果你把一个鸡蛋丢下去),it breaks.
2. If you blow on a candle, (它就熄灭了).
3. If her mother (听从医生的建议),she would/might have got well earlier.
4. If I (没有搭错车),I wouldnt have missed the contest.
5. (如果你认为) treating a woman well means always getting her permission for things,think again.
6. (如果我是你),I would take an umbrella.
7. (如果没有水和空气),there would be no living things on the earth.
8. If (她下周一来这儿的话) next Monday,I would tell her about the matter.
Keys:1. If you drop an egg 2. it is out 3. had taken the doctors advice 4. hadnt taken the wrong bus 5. If you think (that) 6. If I were you 7. If there were no air or water 8. she were to be/ should be/ were there