一、第一条件句：
第一条件句是指真实条件句，主要用于陈述语气，假设的情况可能发生。第一条件句中的动词应该用一般现在时代替一般将来时；用现在完成时代替将来完成时。如：
If Mary goes to the concert, she will bring her brother.
If the weather is fine tomorrow, we shall go to the country.
注意：
在第一条件句中，主句不能用be going to 表示将来，应用shall, will。例如：
If you leave now, you are never going to regret it. (错误)
If you leave now, you will never regret it. (正确)
二、第二条件句：
第二条件句是非真实条件句的一种，它表示现在或将来不可能实现，或实现的可能性很小的一种假设。它的谓语动词所表示的动作、状态都是虚构的、假想的、不可能实现或实现的可能性很小的。第二条件句中的谓语动词用一般过去时或should (were to)+动词原形，而主句中的谓语动词则用would / should / could / might+动词原形。
If I were you, I should not do that.
If everyone in the country knew first aid, many lives would be saved.
注意：
if 条件句中如有were, should, had，可以省去if，并使用倒装语序。
Were I a boy, I would join the army.
在现代英语中，if非真实条件状语从句中的谓语动词如果是be，其过去形式一般用were。
两者的区别在if从句的“条件”上。真实条件句中if从句给出的条件是可以实现的，而虚拟条件句中if从句所给出的条件是与现在情况相反的假设或是不可能实现的。
1.虚拟条件句的结构
虚拟条件句表示与情况相反的愿望、假想等。
(1)虚拟条件句的陈述句结构：If + 从句主语＋动词过去式, 主句主语＋ would ('d) + 动词原形。
1)If I had the time, I'd make something better. 如果有时间的话，我会做些更好吃的东西。
对比either, neither的用法
either意思是"两者中的任何一个"，neither意思是"两者都不"，两个词在句中都可以充当主语、宾语、定语和同位语。
①作主语时，可单独使用，也可以与of连用，either，neither接谓语动词一般用单数形式，但这两者在口语中作主语时，其后的谓语动词也可以用复数。例如：
Either(of them)is OK. (他们两个中)任何一个都行。
②作宾语,可单独使用，也可以与of连用，放在动词或介词之后。例如：
I don't know which book is the better；I shall read both.我不知道这两本书哪一本好，所以我两本都读。
I like neither.(两个)我一个也不喜欢。
③作定语,either和neither后面接单数名词。例如：
On either side of the river there are a lot of trees.河的两边都有许多树。
句中可作主语、宾语和定语。
Neither of the films is good.
两部电影都不好。（没有一部是好的）
Either of the films is good.
（作主语，谓语动词用单数）
两部电影中有一部不错。
He wrote to neither of them.
他没给他们两个任何一个人写信。
He wrote to either of them.(作宾语)
他给他们中的一个人写了信。
Neither teacher often answers the questions.
这两个老师，没有一个经常解答问题。
Either teacher often answers the questions.
这两个老师中有一个常常解答问题。
Both the teachers often answer the questions.（作定语）
这两个老师都常常解答问题。 赞同151| 评论(6)
2)If I didn’t drink so much, I’d be a lot thinner. 如果我没喝那么多酒的话，我会瘦很多。
(2)在虚拟条件句的if从句中，不论从句主语是什么人称，be动词都常用were。在口语和非正式语体中也能见到有人用was。但一般来说就要用were，而且在if I were you中，只能用were.
1)If my grandmother were alive, I'd ask her. 我祖母如果还活着，我会问她的。
2)If I were a man, I’d have to do military service. 如果我是男人，我就得服兵役。
(3)虚拟条件句的疑问句结构：虚拟条件句的疑问句形式只需把主句改为相应的疑问句形式即可，if 引导的从句不用变化。
1)Why would it be better if you ate before you started?
2)Could you get something to eat if you went to the gym after work?
3)What would happen if you didn’t wear long trousers after you finish?
2.虚拟条件句和真实条件句的区别
两者的区别在if从句的“条件”上。真实条件句中if从句给出的条件是可以实现的，而虚拟条件句中if从句所给出的条件是与现在情况相反的假设或是不可能实现的。
(1)If you ask him, he will help you. 如果你向他请求，他会帮助你。（真实条件句，“你向他请求”是可以实现的）
(2)If I were you, I would ask her. 如果我是你，我就会问她。（虚拟条件句，“我是你”这个条件不可能出现）
当与现实情况相反的时候，也用虚拟条件句。
(1)If you ate immediately after the session, you wouldn't feel sick.
(2)If you wore long trousers after exercise, you wouldn't get sore muscles.
(3)If you didn't go to the most popular classes, there wouldn't be so many people.
(4)If you didn't go so fast, you wouldn't get dizzy.
3.虚拟条件句的用法
用虚拟条件句可以表示提出忠告和建议。
(1)If you stretched before you start, you wouldn’t get sore muscles.
(2)If the machine were slower, you wouldn’t get dizzy.
三。第二条件句 虚拟’从句 常见句型
第二条件句经常被称为‘虚拟’从句，因为它用于猜测虚拟或不可能的情况。因此，第二条件句用于协商，可以在讨价还价时提出尝试性建议；但成功的可能性比较低。
If + 主语 + 过去时，主语 + would + 动词原形。
If you increased the order size, we would reduce the price.
If we bought 100 boxes, would you give us a discount?
从句的位置可以保留并且两个从句之间也不需要逗号：
例如：
We will pay within 10 days if you reduce the price by 5%.
We would give you a discount if you bought a larger quantity.
单词were + 不定式 和suppose / supposing 是礼貌的形式，用于提出假定的建议：
例如：
1.were + 不定式：
If you were to offer us a 20% discount, we would place a larger order.
If we were to buy 10 chairs, would you give us the cushions for free?
2. suppose, supposing + 从句:
Suppose I increase the order, will you give us a bigger discount?
Supposing we bought 100 boxes, would you give us a discount?
第一条件句是用于谈判的常见句型：
If + 主语 + 现在时，主语 + will / won't + 动词原形.
If you order 1,000 cases, we'll give you a 5% discount.
谈判经历不同的阶段：
1.制定一个初步的建议
2.讨价还价
3.作出让步
4.达成协议
第一条件句的使用表明协议最终达成的可能性。第一条件句用于连接协商者准备作出的让步和如果协议达成的结果。
例如：
让步： 结果：
If we pay immediately, will you offer us a bigger discount?
If you pay immediately, we will offer you a 10% discount.
If you increase your order by 10%, we will reduce the price by 10%.
四。将if条件句的基本规律总结如下：
零条件句：谈论总是发生，一般存在的现象时使用。
句子结构：从句If+一般现在时，主句用一般现在时
If + Simple Present, + Simple Present 或者 Simple Present + If + Simple Present
Examples：
If you boil an egg, it becomes solid.
If you heat something, it becomes hotter.
I always listen to music if I jog.
在零条件句中，我们可以用when代替if
第一条件句：用于描述将来很可能发生的事件
句子结构：从句if+一般现在时，主句将来时（主将从现）
If + Simple Present, + Will 或者 Will+ If + Simple Present
Examples：
Lisa will be very happy if she wins the prize.
If it rains, then we will stay at home.
If I see Sam, I will ask him to give you a call.
第一条件句中，主句可以用shall, can, may等情态动词代替will
第二条件句：用来描述将来不太可能发生的事情，或者和现在事实相反的事件
句子结构：
条件句if+一般过去时，主句would+动词原形
If + Simple Past, + Would + Base Form 或者 Would + Base Form + If + Simple Past
Examples：
If I won a million dollars, I would travel around the world.
She would quit school if her parents agreed.
I would be surprised if I saw pigs in the sky. 或者 You would see John if you were here now.
If things were different, we would be happy.
We would be good friends if she were nicer.
第二条件句中，我们可以用could, should, might代替will
注：第二条件句中只能用were，不用was
第三条件句: 用于描述和过去事实相反的事件
句子结构：从句if+过去完成时，主句would have + 过去分词
If + Past Perfect, + Would have + V3 或者 Would have + V3 + If + Past Perfect
Examples：
If I had woken up on time, I would have taken the bus.
If I had told Sarah the truth, I would have felt much better.
If it hadn't rained yesterday, we would have enjoyed a nice picnic.
第三条件句中可以用should have, could have, might have代替would have
第一条件疑问句
If + 主语 + 现在时, will / won't + 主语 + 动词原形 ？
1. FIRST CONDITIONAL 第一条件句.就系"主将/现, 从现", 用来描述"现在/未来,实际的情况".
例子:
If the lights turn red, I will stop the car.
如果红灯,我会停车.
if后面的半句, 系条件(conditional), 再后面半句, 系"未来的实际情况"(可以停到车).
2. SECOND CONDITIONAL 第二条件句
second都系讲"现在/未来的情况", 但是系"与现实不符的情况"..
例子:
If I didn't have five children, I could afford a car.
如果我没有5个孩子, 我可以买一辆私家车. (她家镇实际上系: 有孩子, 冇车子)
FIRST CONDITIONAL 讲"实际情况" SECOND CONDITIONAL讲"不实际的情况".
五。第一条件句：
If you study harder, you will pass the exam. 就是我们学的简单的那种，没有虚拟的语气，常规的条件状语从句。
第二条件句：If you studied harder, you would pass the exam.
这时有虚拟语气，主句、从句都把时态较第一条件句后退一步，表示与“现在”的情况相反。
第三条件句：If I had studied harder, I wouldn’t have failed.
这时也有虚拟语气，主句、从句又都把时态较第二条件句后退一步，表示与“过去”的情况相反。
错综条件句：If I were more diligent, I wouldn’t have failed.
If I had studied harder, I wouldn’t get a job like this.
主句与从句动作发生的时间不一致，其实就是把第二、三条件句的从句、或主句交换一下。
含有had、were、should的虚拟条件句可以省略if，并倒装：
Were I you, I would take an umbrella.
Should you come next month, I would tell you something about your father.
Had they got there earlier, they would have become the most popular band.
还有一些条件句是隐藏起来的，即没有if，而是由其他介词或连词来体现：
But for his help, we would still be working.
Without your instructions, I would not have been the mayor of the town.
We didn’t know him. Otherwise we might have been arrested.
虚拟条件句当中，主句或从句二者可以省略一个，表达某种强烈的情感：
You need not have accept his apology.
You should have told me that.
I could have ordered the train ticket.
If I were at home. If only you had not been so ambitious.
一些由动词的特殊含义引起的虚拟：
I wish I had your brains. I wish I had not said that.
wish后从句不用情态动词表示虚拟，时态倒退一格即可，wish本身涵义与情态动词虚拟有点冲突，你能想象：I wish I could have gone with him last night.中，wish和could同时存在吗？
I insisted the committee (should)accept his proposal.
The officer ordered everyone in the army (should)cut their long hair.
They suggested the company (should)kick the black sheep out.
should表示“应当而未”的意思，常用于对现在的虚拟
She locked all the windows for fear that/ lest/ in case thieves (should) come in.
在这种目的状语从句中，should意思是“万一”，表示几率极低（其实就是等于说几率是0，这种情况不可能）
有些表达观点的形容词后也可以跟虚拟语气：
It's a pity that he (should)drive his both parents out.
It's surprising that he (should)miss the last bus.
It's necessary that everyone (should)be on his own.
It's natural that he(should) lead the team.
FIRST CONDITIONAL, 主句用一般现在/将来时(也包括may, can), 从句用一般现在时.
SECOND CONDITIONAL 主句用一般过去时, 从句也是一般过去时.
