If和unless引导的条件状语从句的用法
if引导的条件状语从句
由引导词if或unless引导的状语从句叫做条件状语从句。条件状语从句用来说明主句动作发生的条件，即某一件事情（从句中的动作）实现之后，其他事情（主句中的动作）方能发生。其中if是“如果，假如”的意思。
if引导的条件状语从句使用须知：
一、位置
if引导的条件状语从句，既可放在主句之前也可放在主句之后。当从句置于主句之前时，常用逗号与主句隔开。例如：
You will catch the bus if you get up early.
=If you get up early, you will catch the bus.
如果你早起的话，就能赶上公共汽车。
二、时态
（1）若主句是一般将来时，if引导的从句用一般现在时
If it rains tomorrow, I’ll stay at home. 如果明天下雨，我将呆在家里（2）如果主句是祈使句或含情态动词can, may, must等时，从句也用一般现在时。
例如：
You must see the doctor if you are ill. 如果你生病了，你必须去看医生。
If you want to go skating, wear warm clothes. 如果你想去滑冰，穿上暖和的衣服。
三、主句不能用be going to 表示将来，只能用will.
四、宾语从句中的if与条件状语从句if的区别。宾语从句中的if“是否”相当于 wh ether，引导宾语从句，时态需根据语境确定。如果主句用一般现在时，从句可以根据具体情况选用时态，如果主句用一般过去时，从句必须用过去式的某种形式。
I don’t know if it will rain tomorrow.
我不知道明天是否会下雨。
The old woman asked me if I knew the way to the hospital.
老妇人问我是否知道去医院的路。
unless引导的条件状语从句使用须知：
unless也可引导条件状语从句，意思是“如果不；除非”，相当于if…not…
We’ll go for a picnic if it doesn’t rain this Sunday
=We’ll go for a picnic unless it rains this Sunday.
if ,unless
If，unless 一结构 If 作“如果”解，用来引导条件状语从句，可放在主语前面或后面。二时态 1 当谈论未来可能出现的情况时,主句用一般将来时,if从句用一般现在时。 例：If I am free, I will come to see you . 2 当谈论可预测的、反复出现的情况时，主句和if 句都用一般现在时，此时if 相当于when. 这类句子通常表示不受时间限制的自然法则表普通真理和客观事实 例：If you cool the water below zero, it turns into ice. 三转换 If 从句和主句还可以由“祈使句+and/or+简单句代替”，and 表示句意顺承；or则意为“否则”。 If you study hard, you will pass the exam. = Study hard, and you’ll pass the exam. If you don’t hurry up, you’ll miss the train. = Hurry up, or you’ll miss the train. 另外，unless 也可以引导条件状语从句，相当于if…not,“如果不、除非”。 I will plant the flowers if it doesn’t rain tomorrow. = I will plant the flowers unless it rains tomorrow. Unless: conj. 除非, 如果不 Unless you take more care, you’ll have an accid ent. 如果不多加小心的话，你会出事故的。 更详细的如下 一、unless的基本用法 unless“除非……如果不……”引导否定意义的真实条件句有时也可引导非真实条件句 (1)主句为肯定句。 Unless I visit every bookstore in town．I shall not know whether I can get what want． 如果我不到城里每一家书店去看看，我就不知道是否能买到我想要的书。 You will miss the bus unless you hurry up．你要不快点就会错过班车。 (2)主句为否定句。 I wouldn't be saying this unless I were sure of the facts． 要是我对这些事情没有把握，我就不说这话了。 二、应注意的一些问题 1．unless不能与if'"not换用的情况 unless在意义上相当于if...not，因此在有些场合中unless与if...not可互换使用。
if引导的条件状语从句讲解和练习(答案)
t 条件状语从句 一、 条件状语从句通常由 if （如果）, unless （除非），as long as （只要）引导。 例如：If it rains tomorrow, we won ’go to the park. 如果明天下雨，我们就不去公园了。 Unless weather stops me, I go for a walk every. 我每天都会去散步，除非遇上坏天气。 Our parents will be pleased with our performance as long as we try our best. 小试牛刀：1、只要我们竭尽全力，父母就会满意我们的表现。 Our parents will be pleased with our performance _____ _____ ______ we try our best. 2、如果人人为保护环境做出贡献，世界将会变得更美好。______ ______ ______ _____ _______ to protecting the environment, the world will become much more beautiful. 二、if 引导的条件状语从句 （1）“if 从句+祈使句”的句子。其实，if 作为一个连词，主句也可以是其他形式的句子。 例如：If you want to go, please let me know. If the green light isn ’t on, wait for a minute. (2)“祈使句 + and (or)+ 陈述句” 在意思上相当于一个带有条件状语从句的复合句。 注意：A. “祈使句 + and + 陈述句”可以转化为 if 引导的肯定条件状语从句，而且主语是第二人称。 B. “祈使句 + or + 陈述句”可以转化为 if 引导的否定条件状语从句，而且主语是第二人称。 例如：Study hard and you will pass the exam. =If you study hard, you will pass the exam. Hurry up, or you ’ll be late. =If you don ’t hurry up, you ’ll be late. 考题 (2010 重庆中考)Work hard ，________ you may catch up with your classmates soon. A.or B.but C.and D.yet 思路解析：本句是“祈使句＋and”的句型，句意为“努力学习，你会很快赶上其他同学的”，and 在句中表示承接 关系，所以选 C 项。答案：C 黑色陷阱：本题的陷阱是句型，本句型区别于“祈使句＋or”，这个句型的含义是“……，不然的话/否则……”。 绿色通道：祈使句后面既可以加 and ，也可以加 or ，所以要全面分析句意，再作决定。 小试牛刀：用 if 连接下列句子 1、Go to bed early and you will have a good rest. 2、Hurry up, or you ’ll miss the bus. 三、if 从句与主句具有以下特点： 1．If 从句中用一般现在时，表示未来的一种条件，从句中可以加时间状语。 e.g.If yo u can’t come tomorrow, we can hold the party a little later.明天你如果不能来，我们可迟一点举行宴会。
If引导条件状语从句的详细用法解答
If引导条件状语从句的详细用法解答 引导条件状语从句最常用的连词是if，常见的if条件状语从句表示在某条件下，某事很可能发生，条件是可能存在的，主句中某种情况发生的概率也是很高的。如： If you ask him，he will help you．如果你请他帮忙，他会帮你的。 If you fail in the exam，you will let him down．如果你考试不及格，你会让他失望的。 If you have finished the homework，you can go home．如果你作业做完了就可以回家了。 另外，if从句还表示不可实现的条件或根本不可能存在的条件，也就是一种虚拟的条件或假设。从句多用一般过去时或过去完成时，表示对现在或过去的一种假设。如： If I were you，I would invite him to the party．如果我是你，我会邀请他参加聚会。 I would have arrived much earlier if I had not been caught in the traffic．要不是交通堵塞，我本会来得早一些。 另外你还要注意if 条件句的时态搭配 1．if从句用一般现在时，主句用一般将来时 If he runs he’ll get there in time. 如果他用跑的，他就会及时赶到那儿。 The cat will scratch you if you pull her tail. 如果你拉猫的尾巴，它就会抓你。2．if从句用一般现在时，主句用may/might/can If the fog gets thicker the plane may/might be diverted. 如果雾在大一些，飞机可能就会改在别的机场降落。 If it stops snowing we can go out. 如果雪停了，我们就可以出去。 3．if从句用一般现在时，主句用must/should If you want to lose weight you must/should eat less bread. 如果你想减肥，你必须少吃面包。 4．if从句用一般现在时，主句用一般现在时 If you heat ice it turns to water. (也可用will turn)如果把冰加热，它就会化成水。5．if从句用现在进行时，主句用一般将来时 If you are looking for Peter you’ll find him upstairs. 如果你是在找彼得，上楼就会找到他。 6．if从句用现在完成时，主句用一般将来时 If you have finished dinner I’ll ask the waiter for the bill. 如果你吃完了，我就叫服务生来算账 注意： 学习" if " 引导的条件状语从句的用法,现在总结一下: if 条件句不一般,几个要点记心间; 条件句,放在前,逗号要放句中间。 条件句表可能，主句多用将来时； 条件句表事实，主句常用现在时。
if引导的条件状语从句
语法10单元语法再现梁老师组稿2017-12-31 一、观察下面的句子 If you go to the party, you will have a great time. If you do , you will be late. If you do,you will be sorry. If they have it today, half the class won’t come. If we ask people to bring food, they will just bring potato chips and chocolate. 以上几个句子中“if”有相同的含义“如果”，引导条件状语从句逗号后面的句子是主句。整个连起来的大句子叫主从复合句。 注意主句和从句的时态有什么特点。 总结：If引导的条件状语从句用一般现在时，主句用一般将来时。 简称“主将从现” 练习：（1）If you ______(come)here, you ___________(be) happy. (2) If it _________(rain) tomorrow, we__________(not, go) to the park. (3) If he _________(come) here, I ___________(call) you. (4) If it ___________(not rain), we _________(have) a picnic(野餐). (5) If we do that, more people _________(want) to play the games. 页脚内容1
由if引导的条件状语从句用法
我们以前学习过由if引导的真实条件句，学生对条件状语从句有了个大概的认识，但从教学反馈来看，学生对真实条件句的时态（主将从现）把握并不是很好。这一节内容，围绕What would you d o if you had a million dollars? 展开想像，这是一个轻松的话题，学生也感兴趣，因此教学中要充分利用话题调动学生积极性，使学生多操练，然后进行归纳和总结。更全面比较真实条件句和虚拟语气的区别。在教学中，学生可能比较难把握的是什么是真实条件什么是百真实条件，对虚拟语气的时态也会难以适应，教学中要多强调。 教学目标 1知识目标：掌握虚拟语气的结构并能运用，学会用虚拟语气谈论一些假设的虚拟的情况。2能力目标：培养学生根据情景发挥想像的能力，进行发散思维训练。 3情感、态度和价值观：通过本节课 , 激发学生对社会的关注 , 增强奉献意识 , 使学生形成积极的情感态度 , 教学重点和难点 1虚拟语气的结构和运用（ If+ 主语 +did(were), 主语 + would + do. What would you do if you had a million dollars? I’d give the money to charity If I were you, I’d take a small present. 2虚拟语气与真实条件句的区别。 If it rains this weekend, I will stay at home. If it rained now 事实上现在没下雨 ), I would read a book.
教学过程 （教学过程的表述不必详细到将教师、学生的所有对话、活动逐字记录，但是应该把主要教学环 节、教师活动、学生活动、设计意图很清楚地再现。） Step1 Greeting Step2 Warming-up Step3 1a Step4 Listening (1b) Step5 Pair-work Step6 Summary Ask : How are you today? How ’ s the weather today? What are you going to do after school? What will you do if it rains after school? If 引导的真实条件句时态：主将从现 ut one hundred Yuan and ask W hat would you do if it was yours? Etc. Help the students to answer :I would buy a pair of shoes. 3. 指出虚拟条件句 :If + 主语 +did(were), 主语 +would + do.
unless 与 if not
Unless 与 if not 1. unless 与if … not 都可以用来引导条件状语从句， unless 的语气较重，从句中的动词用一般现在时代替一般将来时。例如： We will visit the Great Wall tomorrow unless it rains. 除非明天下雨，否则我们就去参观长城。 I won't believe what you said unless I've seen it with my own eyes. 我要亲眼所见才能相信你所说的。 Don't enter the lab unless you are permitted to. 只有经过允许才能进入实验室。 2. 有的同学在遇到使用 unless 的句子时，弄不清该用肯定还是否定而出错。这时最好的办法是将 unless 替换成if … not 的结构，从而就一目了然了。例如： I won't go to the party unless I am invited. （ =I won't go to the party if I am not invited. ） 如果没有人邀请我，我是不会去参加聚会的。 3. 由于 unless 与if … not 的语气不同，有时两者替换后，其意思就不一样了。例如： Unless he were my friend, I shouldn't expect his help. 除非他是我的朋友，我才会期待他的帮助。（本句的潜在意思为：他并不是我的朋友。） If he were not my friend, I shouldn't expect his help. 如果他不是我的朋友，我就不会期待他的帮助了。（本句的潜在意思为：正因为他是我的朋友，我才会期待他的帮助。） 4. 在平时使用过程中，要注意 unless 与 until 的区别。
初中英语——If引导的条件状语从句
初中英语――if引导的条件状语从句 在主从复合句中修饰主句中的动词、形容词、副词等的从句叫做状语从句，状语从句一般可分为时间状语从句、地点状语从句、原因状语从句、目的状语从句、结果状语从句、条件状语从句、让步状语从句、比较状语从句和方式状语从句九种。 在句子中做条件状语的从句称为条件状语从句。可置于句首、句尾，有时还可置于主语和谓语之间。引导条件状语从句的连接词有：if ,unless,as/so long as等 1.if引导的条件状语从句 表示在某种条件下某事很可能发生。 If we pay much attention to the earth, we'll have a better world. 如果我们多关爱地球，就会拥有一个更美好的世界 If it rains tomorrow, what shall we do? 如果明天下雨，我们怎么办？ 注意：if还可以引导虚拟条件句，表示不可实现的条件，从句中多用一般过去时或过去完成时。 What would happen if there were no water ? 如果没有水会怎样？ 2.unless引导的条件状语从句 unless的意思是如果不，除非。可与if...not互换。 You will fail in English unless you work hard. 你英语考试会不及格的，除非你更加努力。 3.as /so long as引导的条件状语从句 as /so long as意思是“只要” So long as you're happy,i will be happy. 只要你高兴，我就高兴。 4.once引导的条件状语从句 once引导的条件状语从句，意为“一旦...，就”，从句可置于主句前或后 Once you begin,never stop. 一旦开始，就绝不要停止 Maths is easy to learn once you understand the rules. 一旦你理解了规则，数学就不难学了。 提示：在条件状语从句中，用一般现在时代替一般将来时，用一般过去时代替过去将来时。 If the weather is bad next week, we'll put off the climbing. 如果下周天气不好，我们将推迟爬山。 Father told me if i worked hard he would buy me a gift. 爸爸告诉我，如果我努力学习，他会给我买一份礼物。
if条件句和should的用法
If 引导条件句的用法 1、真实条件句用于陈述语气，假设的情况可能发生，其中if 是如果的意思。时态关系 句型：条件从句主句 一般现在时shall/will + 动词原形 If he comes, he will bring his violin. 典型例题 The volleyball match will be put off if it ___. A. will rain B. rains C. rained D. is rained 答案B。真实条件句主句为将来时，从句用一般现在时。 注意： 1）在真实条件句中，主句不能用be going to表示将来，该用shall, will. (错) If you leave now, you are never going to regret it. (对) If you leave now, you will never regret it. 2）表示真理时，主句谓语动词便不用shall (will) +动词原形，而直接用一般现在时的动词形式。 2 非真实条件句 1）时态：可以表示过去，现在和将来的情况。它的基本特点是时态退后。 a. 同现在事实相反的假设。 句型：条件从句主句 一般过去时should( would) +动词原形 If they were here, they would help you. b. 表示于过去事实相反的假设。 句型：条件从句主句 过去完成时should(would) have+ 过去分词 If she had worked harder, she would have succeeded. The rice would not have been burnt if you had been more careful. If my lawyer had been here last Saturday, he would have prevented me from going. If he had come yesterday, I should / would have told him about it. 含义：He did not come yesterday, so I did not tell him about it. If he had not been ill and missed many classes, he would have made greater progress. 含义：He was ill and missed many lessons, so he did not make greater progress. c. 表示对将来的假想 句型：条件从句主句 一般过去时should+ 动词原形 were+ 不定式would + 动词原形 should+ 动词原形
if和unless区别和练习
C h a p t e r1语法If 和unless引导的条件状语从句 我们用if引导的条件状语从句来讨论可能的条件以及该条件成立时可能的结果。一. 学习if引导的条件状语从句的用法，我们可先从如下的口诀入手： If条件句不一般，几个要点记心间； 条件句，放在前，逗号要句中间 条件句表可能，主句多用将来时； 条件句表事实，主句常用现在时。 We can walk there if we can’t find a bus. 如果我们找不到公车，也能走路去那里 主句条件状语从句 If it rains tomorrow, we will not go to the zoo. 如果明天下雨，我们就不去动物园 条件状语从句主句 What will you go if you find someone in danger? 主句条件状语从句 如果你发现某人有危险，你会怎么做？ If 条件句有不同的类型，简述如下： 1. 用if条件句表达客观真理或普通现象 If条件句用于表达客观真理或普通现象时，主，从句时态均用一般现在时，如：Eg. If you freeze water, it turns into ice. A fish dies if you take it out of water. 2. 用if 条件句表示将来可能发生的事情 在表示将来可能发生的事情的if条件句中，主句用一般将来时，而if从句用一般现在时表示将来的时间，即主将从现
Eg. If I like the house, I will buy it. 如果我喜欢这房子，我就会把它买下 I will tell her if I see her. 如果我见到她，我就会告诉她。 主句中的will也可以用情态动词can, may 或might等代替。如： Eg. If they are friendly，I might invite them to the party. 如果他们很友善，我可能会请他们去参加聚会 If we hurry now, we can stop for coffee later. 如果我们现在抓紧时间，就可以稍后去喝咖啡注意：在条件句中，主句部分只能使用动词will的一般将来时，不能使用be going to的结构 二. Unless 的条件句 表示在特定条件下，才决定做或不做一件事，中文用的连接词一般是“除非”和“否则”。如：除非刮台风，否则演唱会将如期进行。在英语中，我们可以用unless表达这个意思，相当于if not。以这个句子为例： The concert will be held as schedule unless there is a typhoon. = the concert will be held as schedule if there is not a typhoon She will keep on singing unless she is told to stop. 她会一直唱下去，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(否则) 来做同义句转换 Unless you listen carefully, you won’t know the answer. = if you don’t listen carefully, you won’t know the answer. = you should listen carefully, or you won’t know the answer. 深圳中考题： 1. If I ________ his phone number, I will tell you. A.find B. found C. will find D. have found 2. We will go camping if it _______ tomorrow.
if条件状语从句专练
If条件状语从句专练 1. If I ___(go) to the party, they ___(be) upset. 2. If I ___(take) a taxi, it ___(be) too expensive. 3. If she ___(finish) work early, she can go home. 4. If the weather is fine, we ____(go) for a walk. 5. If I ___(have) time tonight, I will finish the book. 6. If it ___(rain) next Sunday, we won`t be able to plant trees. 7. If she ___(arrive) home, she will phone
me. 8. Unless you speak to him first, she ___(not speak) to you. 9. If he ___ (call) to you, tell him I will ring back. 10. I don`t know if it ___(rain) tomorrow. 11. Have a rest if you ___(be) tired. 12. Don`t come unless I ___(call) you. 13. I don`t know if he ___(come) tomorrow, but if he __(come), I`ll let you know. 宾语从句与状语从句混合 1. ——Helen, do you know if Martin
if与unless专项练习
If, unless 专项练习 一、完成下列句子 1. I’m sure if he _____(go) to the party, he________ (have) a great time. 2. If the rain _______(stop) tonight, we will go to the cinema. 3. I’ll buy a computer if I ______(have) enough money. 4. You _________(not get) nervous if you _____(do ) enough exercise. 5. I want to know if he _________(come) tomorrow, if he _______(come), I __________(give) the massage to him. 6. Comrade Wang didn't know if there _______ (be) on English evening that day. 7. Please tell me if she _______ (come) again next time. 8. Mike asked me if we _______(ask) any questions the next class. 9．The twins ______________ (fight) if they_______________ (argue). 10. I ____________ (have) a bake sale if I _____________ (need) money for education. 二、选择 ( )1. I don’t know _____ he will come tomorrow. _____ he comes, I’ll tell you. A. if; Whether B. whether; Whether C. if; That D. if; if ( ) 2. He said he would help me with my maths if he _______ free. A．was B．will be C．would be D．is ( ) 3. Tommy, do you know if Frank ________ to the zoo this Sunday if it ________? -Sorry, I have no idea. A. will go; is fine B. goes; is fine C. will go; is going to be fine D. goes; will be fine ( ) 4. -Listen! It is still noisy in the head teacher’s office. -Go and see ________ they have finished correcting the papers yet. A. though B. whether C. unless D. while ( ) 5. He asked me ________ we could go to Beijing to watch the game by plane. A. that B. if C. how D. what （）6 . The volleyball match will be put off if it ______. A. will rain B. rains C. rained D. is raining （）7. Difficulties are nothing if we ______ not afraid of them A. will B. shall C. are D. do （）8. I don’t like to be interrupted if I______. A. speak B. will speak C. am speaking D. spoke （）9. If you______ the book you will understand the story better. A. will be reading B. have read C. will have read D. read ( ) 10. There is going to______ a sports meeting next week. If it ______ , we’ll have to cancel it.. A. be; will rain B. have; will rain C. be; rains D. give; is going to rain （）11. If you ______ a chance to study in a foreign country, just take it. A. getting B. had got C. will get D. get ( ) 12. I want to know if they ____ the spring sports meeting next month. If they ____ it, I must get ready for it. A. hold; will hold B. will hold; hold C. hold; hold D. will hold; will hold （）13. –Look, what have you done? -Sorry. I think if I ________ another chance, I’ll do it better. A. give B. will be given C. will give D. am given （）14.If you _______ him tomorrow, please ask him if he ______ to work on the farm with us. A. see ; goes B. will see; goes C. will see; will go D. see; will go ( ) 15. It makes no difference __________. A. whether will you come tomorrow. B. Whether or not will be pass the exam C. If he will come to the meeting or not D. Whether he will come to the meeting or not ( ) 16. Even now many people still remembered ________ when hey heard about the 1976 earthquake in Tangshan. A. what were they doing B.that they were doing C. what they were doing D.if they were doing ( ) 17. In summer, food goes bad easily _____ it is put in the refrigerator. A. until B. if C. unless D. since ( ) 18. –I hear Jack Chan will come to Shanghai next week. -Really? _______ he comes, my younger sister will be very happy. A. If B. Until C. Unless D. Before ( ) 19. We will have no water to drink______ we don’t protect the earth. A．until B. before C. though D. if ( ) 20 –May I surf the Internet now? - No, _______ you have finished doing the dishes.
If 引导的条件状语从句
If 引导的条件状语从句 If 引导的条件状语从句遵循主过从过、主将从现的原则。 主将从现（主情从现、主祈从现） If it rains tomorrow,I won’t climb the hills. If it doesn’t rain tomorrow,I will go to the countryside with my friends. If 引导的条件状语从句 If 引导的条件状语从句遵循主过从过、主将从现的原则。 主将从现（主情从现、主祈从现） If you will help me,I'll finish it on time. We may go out if it's fine tomorrow. If you finish your homework,you can watch TV. Please call me if you go shopping next Sunday. If I go there，I'll take her some flowers. We'll stay at home if it rains tomorrow. Please call me if he’s at home. If you work harder,you’ll pass the exam. She will visit her grandpa if she has time tomorrow. We’ll take a taxi to the city if the train doesn’t arrive on time. The teacher will be angry if he is late. If引导的条件状语从句与unless引导的条件状语从句的转换 If+否定形式=unless+肯定形式
(完整版)if引导的条件句中的虚拟语气
if引导的条件句中的虚拟语气 虚拟语气表示一种不能实现的假设。该语法主要用于if条件状语从句。 一、if引导的条件状语从句的分类及虚拟条件句的判断 1、可以把条件句分为两类： 1).真实条件句（Sentences of Real Condition）：凡是假设的情况发生性可能很大，就是真实条件句。例如： ⑴、If I have time , I will help you with this work.如果我有时间会帮助你做此工作的。 (2)、If time permits, we'll go fishing together.(如果有时间的话，我们就一起去钓鱼。） 2).虚拟条件句（Sentences of Unreal Condition）：当假设是不大可能实现时，就是虚拟条件句。例如： ⑴、If I were you , I would have attended the meeting. 如果我是你的话，就去参加会议了。 ⑵、If he had come here yesterday, he would have seen his ol d friend.假如他昨天来这儿的话，就会看见他的老朋友。 ⑴、If it had rained yesterday, we would have stayed at home.（如果昨天下雨的话，我们就会留在家里。） 2、.if条件状语从句中虚拟语气的判断 判断是真实条件句还是非真实条件句。只有在非真实条件句中才使用虚拟语气。通过句子意思，看假设的条件是否能够实现，能
够实现是真实条件句，不能使用虚拟语气；假设的条件不能实现则是非真实条件句，要用虚拟语气。 判断这个假设是与哪个事实相反。通常有三种情况：①与过去事实相反。②与现在事实相反。③与将来事实可能相反。 3、“后退一步法” 后退一步法是指在准确地判断了该句与哪一事实相反后，按虚拟语气的后退一步法处理从句谓语动词的时态。即：在非真实条件状语从句中，谓语动词按正常情况“后退一步”。也就是： ①与过去事实相反，在从句中用过去完成时形式表示。 ②与现在事实相反，在从句中用过去一般时形式表示。 ③与将来事实可能相反，在从句中用过去将来时形式表示。 主句中则用情态动词would, should, could 等加一个与从句一致的动词形式。例： ⑴、If I had come her yesterday, I would have seen him. ⑵、If I were a teacher, I would be strict with my students. ⑶、If it should snow tomorrow, they couldn't go out. 4、注意事项 ①if条件句中如有were, should, had，可以省去if，并使用倒装语序。 ②在现代英语中if条件状与从句中的谓语动词如果是be其过去形式一般用were。
if引导的条件状语从句-与专题练习
if引导的条件状语从句 引导条件状语从句最常用的连词是if，常见的if条件状语从句表示在某条件下某事很可能发生。如： If you ask me ,I will answer you． If it rains tomorrow, I will stay at home. I will stay at home if it rains tomorrow. 另外，if从句还表示不可实现的条件或根本不可能存在的条件，也就是一种虚拟的条件或假设。从句多用一般过去时或过去完成时，表示对现在或过去的一种假设。如： If I were in university，I would …． If I had enough money ,I would buy a car. 1.if从句用一般现在时，主句用一般将来时 If he runs , he’ll get there in time． 2.if从句用一般现在时，主句用may/might/can/must If the fog gets thicker the plane may/might be diverted. 3.if从句用一般现在时，主句用一般现在时 If you heat ice it turns to water. (也可用will turn) 4. if从句用现在进行时，主句用一般将来时 If you are looking for Peter you’ll find him upstairs. 5.if从句用现在完成时，主句用一般将来时 If you have finished dinner I’ll ask the waiter for the bill.
unless的用法
unless的用法 unless是从属连词，引导条件状语从句，含有否定意义，相当于if条件状语从句的否定形式。所以unless = if not。注意：unless引导的条件状语从句和if条件状语从句，与其它时间状语从句一样，用一般现在时代替将来时。 Unless: conj. 除非, 如果不 Unless you take more care, you’ll have an accident. 如果不多加小心的话，你会出事故的。 My baby sister never cries unless she is hungry. 我那刚出生的妹妹除非饿了，否则她是从来不哭的。 Don’t promise anything unless you’re 100 per cent sure. 不要作任何的许诺, 除非你有百分百的把握。 Unless bad weather stops me, I run every day. 除非坏天气作梗，每天我都跑步。 木头容易燃烧，除非是水湿了。 We'll be late unless we speed up. 我们要不加快些，就会迟到了。 You'll fail in English unless you work hard. 除非你努力学习，否则你英语将不及格。 You'll miss the bus unless you walk more quickly. 除非你走快一点，否则将赶不上公共汽车。 You won't hear anything unless you roll the tape ahead. 除非你把录音带往前转，否则你是不会听到任何东西的 You will never pass the exam unless you study harder. 除非你加紧学习，否则考试永远过不了关。 更详细的如下 一、unless的基本用法 连词unless意为“除非……如果不……”，“除了……”，多引导一个否定意义的真实条件句，有时也可引导非真实条件旬。unless引导条件句时，主要用于下列情况。 (1)主句为肯定句。如： Unless I visit every bookstore in town．I shall not know whether I can get what l want．如果我不到城里每一家书店去看看，我就不知道是否能买到我想要的书。 You will miss the bus unless you hurry up．你要不快点就会错过班车。 You’ll fail in chemistry again unless you work harder．如果你不再加把劲，你化学考试还会不及格。 (2)主句为否定句。如： Unless you oil the motor regularly．it won’t run smoothly．要不是你经常给发动机上油。它就不会转得那么顺畅。 I wouldn't be saying this unless I were sure of the facts．要是我对这些事情没有把握，我就不说这话了。 You will never get anywhere unless you have set your goal．如果你不设定目标，你哪儿也去不了。 二、应注意的一些问题 1．unless不能与if'"not换用的情况 unless在意义上相当于if...not，因此在有些场合中unless与if...not可互换使用。