if和unless的用法講解

1、Chapter 1 語法 If 和 unless引導(dǎo)的條件狀語從句我們用if引導(dǎo)的條件狀語從句來討論可能的條件以及該條件成立時(shí)可能的結(jié)果。一. 學(xué)習(xí)if引導(dǎo)的條件狀語從句的用法，我們可先從如下的口訣入手：If條件句不一般，幾個(gè)要點(diǎn)記心間；條件句，放在前，逗號(hào)要句中間條件句表可能，主句多用將來時(shí)；條件句表事實(shí)，主句常用現(xiàn)在時(shí)。We can walk there if we cant find a bus. 如果我們找不到公車，也能走路去那里主句 條件狀語從句If it rains tomorrow, we will not go to the zoo. 如果明天下雨，我們就不去動(dòng)物園條件狀語從句

2、 主句What will you go if you find someone in danger? 主句 條件狀語從句如果你發(fā)現(xiàn)某人有危險(xiǎn)，你會(huì)怎么做？If 條件句有不同的類型，簡(jiǎn)述如下：1. 用if條件句表達(dá)客觀真理或普通現(xiàn)象 If條件句用于表達(dá)客觀真理或普通現(xiàn)象時(shí)，主，從句時(shí)態(tài)均用一般現(xiàn)在時(shí)，如：Eg. If you freeze water, it turns into ice. A fish dies if you take it out of water. 2. 用if 條件句表示將來可能發(fā)生的事情 在表示將來可能發(fā)生的事情的if條件句中，主句用一般將來時(shí)，而if從句用一般現(xiàn)在時(shí)表

3、示將來的時(shí)間，即主將從現(xiàn) Eg. If I like the house, I will buy it. 如果我喜歡這房子，我就會(huì)把它買下 I will tell her if I see her. 如果我見到她，我就會(huì)告訴她。主句中的will也可以用情態(tài)動(dòng)詞can, may 或might等代替。如：Eg. If they are friendly，I might invite them to the party. 如果他們很友善，我可能會(huì)請(qǐng)他們?nèi)⒓泳蹠?huì)If we hurry now, we can stop for coffee later. 如果我們現(xiàn)在抓緊時(shí)間，就可以稍后去喝咖啡注意：

4、在條件句中，主句部分只能使用動(dòng)詞will的一般將來時(shí)，不能使用be going to的結(jié)構(gòu)二. Unless 的條件句表示在特定條件下，才決定做或不做一件事，中文用的連接詞一般是“除非”和“否則”。如：除非刮臺(tái)風(fēng)，否則演唱會(huì)將如期進(jìn)行。在英語中，我們可以用unless表達(dá)這個(gè)意思，相當(dāng)于if not。以這個(gè)句子為例：The concert will be held as schedule unless there is a typhoon.= the concert will be held as schedule if there is not a typhoonShe will keep

5、on singing unless she is told to stop. 她會(huì)一直唱下去，除非有人叫她停止= she will keep on singing if she is not told to stop也可以用or(否則) 來做同義句轉(zhuǎn)換Unless you listen carefully, you wont know the answer. = if you dont listen carefully, you wont know the answer.= you should listen carefully, or you wont know the answer.深圳中

6、考題：1. If I _ his phone number, I will tell you.A. find B. found C. will find D. have found2. We will go camping if it _ tomorrow.A. Wont rain B. didnt rain C. doesnt rain D. isnt raining3. Im waiting for my friend. If he _, I _ swimming alone.A. doesnt come; will go B. wont come; will go C.will come

7、; wont go D. dont come; will go4. _ you go to the supermarket at 7 p.m, you can buy a lot of cheap food.A. If B. Unless C. Whether D. When5. I wont get to the party on time _ I catch the first train tomorrow morning.A. If B. Unless C. Whether D. When6. -Shall we go on a picnic this weekend? -Good id

8、ea! Unless it _.A. rains B. doesnt rain C. rain D. wont rain7. -Can I change the jacket for another one _ it doesnt fit me well? - Of course.A. unless B. if C. that D. though8. Nobody can learn maths well he works hard on it.A if B unless C thought D however9. If fish away from water, they die.A are taking, wont B are taken, will C are being taken, will D take, w