一、第一條件句：
第一條件句是指真實條件句，主要用于陳述語氣，假設的情況可能發(fā)生。第一條件句中的動詞應該用一般現(xiàn)在時代替一般將來時；用現(xiàn)在完成時代替將來完成時。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：
在第一條件句中，主句不能用be going to 表示將來，應用shall, will。例如：
If you leave now, you are never going to regret it. (錯誤)
If you leave now, you will never regret it. (正確)
二、第二條件句：
第二條件句是非真實條件句的一種，它表示現(xiàn)在或將來不可能實現(xiàn)，或實現(xiàn)的可能性很小的一種假設。它的謂語動詞所表示的動作、狀態(tài)都是虛構的、假想的、不可能實現(xiàn)或實現(xiàn)的可能性很小的。第二條件句中的謂語動詞用一般過去時或should (were to)+動詞原形，而主句中的謂語動詞則用would / should / could / might+動詞原形。
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 條件句中如有were, should, had，可以省去if，并使用倒裝語序。
Were I a boy, I would join the army.
在現(xiàn)代英語中，if非真實條件狀語從句中的謂語動詞如果是be，其過去形式一般用were。
兩者的區(qū)別在if從句的“條件”上。真實條件句中if從句給出的條件是可以實現(xiàn)的，而虛擬條件句中if從句所給出的條件是與現(xiàn)在情況相反的假設或是不可能實現(xiàn)的。
1.虛擬條件句的結構
虛擬條件句表示與情況相反的愿望、假想等。
(1)虛擬條件句的陳述句結構：If + 從句主語＋動詞過去式, 主句主語＋ would ('d) + 動詞原形。
1)If I had the time, I'd make something better. 如果有時間的話，我會做些更好吃的東西。
對比either, neither的用法
either意思是"兩者中的任何一個"，neither意思是"兩者都不"，兩個詞在句中都可以充當主語、賓語、定語和同位語。
①作主語時，可單獨使用，也可以與of連用，either，neither接謂語動詞一般用單數(shù)形式，但這兩者在口語中作主語時，其后的謂語動詞也可以用復數(shù)。例如：
Either(of them)is OK. (他們兩個中)任何一個都行。
②作賓語,可單獨使用，也可以與of連用，放在動詞或介詞之后。例如：
I don't know which book is the better；I shall read both.我不知道這兩本書哪一本好，所以我兩本都讀。
I like neither.(兩個)我一個也不喜歡。
③作定語,either和neither后面接單數(shù)名詞。例如：
On either side of the river there are a lot of trees.河的兩邊都有許多樹。
句中可作主語、賓語和定語。
Neither of the films is good.
兩部電影都不好。（沒有一部是好的）
Either of the films is good.
（作主語，謂語動詞用單數(shù)）
兩部電影中有一部不錯。
He wrote to neither of them.
他沒給他們兩個任何一個人寫信。
He wrote to either of them.(作賓語)
他給他們中的一個人寫了信。
Neither teacher often answers the questions.
這兩個老師，沒有一個經(jīng)常解答問題。
Either teacher often answers the questions.
這兩個老師中有一個常常解答問題。
Both the teachers often answer the questions.（作定語）
這兩個老師都常常解答問題。 贊同151| 評論(6)
2)If I didn’t drink so much, I’d be a lot thinner. 如果我沒喝那么多酒的話，我會瘦很多。
(2)在虛擬條件句的if從句中，不論從句主語是什么人稱，be動詞都常用were。在口語和非正式語體中也能見到有人用was。但一般來說就要用were，而且在if I were you中，只能用were.
1)If my grandmother were alive, I'd ask her. 我祖母如果還活著，我會問她的。
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)虛擬條件句的疑問句結構：虛擬條件句的疑問句形式只需把主句改為相應的疑問句形式即可，if 引導的從句不用變化。
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.虛擬條件句和真實條件句的區(qū)別
兩者的區(qū)別在if從句的“條件”上。真實條件句中if從句給出的條件是可以實現(xiàn)的，而虛擬條件句中if從句所給出的條件是與現(xiàn)在情況相反的假設或是不可能實現(xiàn)的。
(1)If you ask him, he will help you. 如果你向他請求，他會幫助你。（真實條件句，“你向他請求”是可以實現(xiàn)的）
(2)If I were you, I would ask her. 如果我是你，我就會問她。（虛擬條件句，“我是你”這個條件不可能出現(xiàn)）
當與現(xiàn)實情況相反的時候，也用虛擬條件句。
(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.虛擬條件句的用法
用虛擬條件句可以表示提出忠告和建議。
(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。第二條件句 虛擬’從句 常見句型
第二條件句經(jīng)常被稱為‘虛擬’從句，因為它用于猜測虛擬或不可能的情況。因此，第二條件句用于協(xié)商，可以在討價還價時提出嘗試性建議；但成功的可能性比較低。
If + 主語 + 過去時，主語 + would + 動詞原形。
If you increased the order size, we would reduce the price.
If we bought 100 boxes, would you give us a discount?
從句的位置可以保留并且兩個從句之間也不需要逗號：
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.
單詞were + 不定式 和suppose / supposing 是禮貌的形式，用于提出假定的建議：
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 + 從句:
Suppose I increase the order, will you give us a bigger discount?
Supposing we bought 100 boxes, would you give us a discount?
第一條件句是用于談判的常見句型：
If + 主語 + 現(xiàn)在時，主語 + will / won't + 動詞原形.
If you order 1,000 cases, we'll give you a 5% discount.
談判經(jīng)歷不同的階段：
1.制定一個初步的建議
2.討價還價
3.作出讓步
4.達成協(xié)議
第一條件句的使用表明協(xié)議最終達成的可能性。第一條件句用于連接協(xié)商者準備作出的讓步和如果協(xié)議達成的結果。
例如：
讓步： 結果：
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。將if條件句的基本規(guī)律總結如下：
零條件句：談論總是發(fā)生，一般存在的現(xiàn)象時使用。
句子結構：從句If+一般現(xiàn)在時，主句用一般現(xiàn)在時
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.
在零條件句中，我們可以用when代替if
第一條件句：用于描述將來很可能發(fā)生的事件
句子結構：從句if+一般現(xiàn)在時，主句將來時（主將從現(xiàn)）
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.
第一條件句中，主句可以用shall, can, may等情態(tài)動詞代替will
第二條件句：用來描述將來不太可能發(fā)生的事情，或者和現(xiàn)在事實相反的事件
句子結構：
條件句if+一般過去時，主句would+動詞原形
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.
第二條件句中，我們可以用could, should, might代替will
注：第二條件句中只能用were，不用was
第三條件句: 用于描述和過去事實相反的事件
句子結構：從句if+過去完成時，主句would have + 過去分詞
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.
第三條件句中可以用should have, could have, might have代替would have
第一條件疑問句
If + 主語 + 現(xiàn)在時, will / won't + 主語 + 動詞原形 ？
1. FIRST CONDITIONAL 第一條件句.就系"主將/現(xiàn), 從現(xiàn)", 用來描述"現(xiàn)在/未來,實際的情況".
例子:
If the lights turn red, I will stop the car.
如果紅燈,我會停車.
if后面的半句, 系條件(conditional), 再后面半句, 系"未來的實際情況"(可以停到車).
2. SECOND CONDITIONAL 第二條件句
second都系講"現(xiàn)在/未來的情況", 但是系"與現(xiàn)實不符的情況"..
例子:
If I didn't have five children, I could afford a car.
如果我沒有5個孩子, 我可以買一輛私家車. (她家鎮(zhèn)實際上系: 有孩子, 冇車子)
FIRST CONDITIONAL 講"實際情況" SECOND CONDITIONAL講"不實際的情況".
五。第一條件句：
If you study harder, you will pass the exam. 就是我們學的簡單的那種，沒有虛擬的語氣，常規(guī)的條件狀語從句。
第二條件句：If you studied harder, you would pass the exam.
這時有虛擬語氣，主句、從句都把時態(tài)較第一條件句后退一步，表示與“現(xiàn)在”的情況相反。
第三條件句：If I had studied harder, I wouldn’t have failed.
這時也有虛擬語氣，主句、從句又都把時態(tài)較第二條件句后退一步，表示與“過去”的情況相反。
錯綜條件句：If I were more diligent, I wouldn’t have failed.
If I had studied harder, I wouldn’t get a job like this.
主句與從句動作發(fā)生的時間不一致，其實就是把第二、三條件句的從句、或主句交換一下。
含有had、were、should的虛擬條件句可以省略if，并倒裝：
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.
還有一些條件句是隱藏起來的，即沒有if，而是由其他介詞或連詞來體現(xiàn)：
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.
虛擬條件句當中，主句或從句二者可以省略一個，表達某種強烈的情感：
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.
一些由動詞的特殊含義引起的虛擬：
I wish I had your brains. I wish I had not said that.
wish后從句不用情態(tài)動詞表示虛擬，時態(tài)倒退一格即可，wish本身涵義與情態(tài)動詞虛擬有點沖突，你能想象：I wish I could have gone with him last night.中，wish和could同時存在嗎？
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“應當而未”的意思，常用于對現(xiàn)在的虛擬
She locked all the windows for fear that/ lest/ in case thieves (should) come in.
在這種目的狀語從句中，should意思是“萬一”，表示幾率極低（其實就是等于說幾率是0，這種情況不可能）
有些表達觀點的形容詞后也可以跟虛擬語氣：
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, 主句用一般現(xiàn)在/將來時(也包括may, can), 從句用一般現(xiàn)在時.
SECOND CONDITIONAL 主句用一般過去時, 從句也是一般過去時.
