1、表示在某條件下，某事很可能發(fā)生，條件是可能存在的，主句中某種情況發(fā)生的概率也是很高的。如：If you ask him, he will help you.如果你請(qǐng)他幫忙，他會(huì)幫你的。If you fail in the exam, you will let him down.If you have finished the homework, you can go home.2、表示不可實(shí)現(xiàn)的條件或根本不可能存在的條件，也就是一種虛擬的條件或假設(shè)。從句多用一般過(guò)去時(shí)或過(guò)去完成時(shí)，表示對(duì)現(xiàn)在或過(guò)去的一種假設(shè)。如： If I were you, I would invite him to the party.---->不能用was如果我是你，我會(huì)邀請(qǐng)他參加聚會(huì)。I would have arrived much earlier if I had not been caught in the traffic.要不是交通堵塞，我本會(huì)來(lái)得早一些。3、表示的是事實(shí)，可用 when 替代 if
Oil floats if you your pour it on water.如果你把油倒在水上，它就會(huì)浮起來(lái)。You must see the doctor if you are ill.
A、if 從句用一般現(xiàn)在時(shí)，主句用一般將來(lái)時(shí)If he runs, he’ll get there in time. 如果他用跑的，他就會(huì)及時(shí)趕到那兒。The cat will scratch you if you pull her tail. B、if 從句用一般現(xiàn)在時(shí)，主句用may/might/canIf the fog gets thicker the plane may/might be diverted. 如果霧在大一些，飛機(jī)可能就會(huì)改在別的機(jī)場(chǎng)降落。If it stops snowing, we can go out. C、if 從句用一般現(xiàn)在時(shí)，主句用must/shouldIf you want to lose weight, you must/should eat less bread. D、if 從句用一般現(xiàn)在時(shí)，主句用一般現(xiàn)在時(shí)(客觀真理)If you heat ice, it turns to water. ---->也可用 will turnE、if 從句用現(xiàn)在進(jìn)行時(shí)，主句用一般將來(lái)時(shí)If you are looking for Peter, you’ll find him upstairs. F、if從句用現(xiàn)在完成時(shí)，主句用一般將來(lái)時(shí)If you have finished dinner, I’ll ask the waiter for the bill. 如果你吃完了，我就叫服務(wù)生來(lái)算賬在 if 引導(dǎo)的條件狀語(yǔ)從句中，條件句位置靈活，可直接放在主句后面，若 if 條件句放句首， 從句后面要加逗號(hào)，和主句隔開(kāi)。if 條件句不一般,幾個(gè)要點(diǎn)記心間；條件句表可能，主句多用將來(lái)時(shí)；條件句表事實(shí)，主句常用現(xiàn)在時(shí)。7、if 有時(shí)可省略，然后將主語(yǔ)與所用的限定動(dòng)詞（尤其是were，had，should）倒置。例如： Should it (= if it should) be necessary, I will go. Were I (= if I were) in your place, I would do the same.Had I (= if I had) known earlier, I would come.如果我早一點(diǎn)知道，我就會(huì)來(lái)。二、if 引導(dǎo)賓語(yǔ)從句，常用于ask、know、find out、wonder等之后，和 whether 意思相同。例如：Lily asked if/whether she liked it. She asked if/whether they had a cotton one．三、if 引導(dǎo)讓步狀語(yǔ)從句，這時(shí) if 當(dāng)作“即使是”，“雖說(shuō)”解。例如：If she's poor, at least she's honest.雖說(shuō)她很窮，但至少她還是誠(chéng)實(shí)的。If I am wrong, you are wrong, too.即使說(shuō)我錯(cuò)了，那么你也不對(duì)。I’ll do it, even if it takes me all the afternoon. 雖然會(huì)花費(fèi)我一下午的時(shí)間，我還是要做這事。 四、if 引導(dǎo)時(shí)間狀語(yǔ)從句，當(dāng) if 做“當(dāng)”或“無(wú)論何時(shí)”解而不含有條件之義時(shí)，if 從句中的時(shí)態(tài)與主句中的時(shí)態(tài)相同。例如： If you mix yellow and blue, you get green.你將黃色與藍(lán)色混合，便會(huì)得到綠色。 If she wants the servant, she rings the bell.每當(dāng)她需要仆人時(shí)，她便按鈴。五、if 后接否定動(dòng)詞，用于感嘆句中，表示沮喪、驚奇等。例如：Well, if I haven't left my false teeth at home!And if he didn't try to knock me down!六、與 will 或 would 連用，表示客氣地請(qǐng)
If you will sit down for a few moments, I'll tell the manager you're here.請(qǐng)稍坐，我這就告訴經(jīng)理說(shuō)您來(lái)了。If you would care to leave your name, we'll contact you as soon as possible.麻煩您留下姓名，我們會(huì)盡快與您聯(lián)系的。七、if 與 as 連用，意為“仿佛，好像”，同樣引導(dǎo)從句。例如：It sounds as if you have grown apart from Tom. 聽(tīng)起來(lái)好像你和湯姆之間產(chǎn)生了隔閡。The whole room looks as if it has been lovingly put together over the years.整個(gè)房間看起來(lái)好像是經(jīng)過(guò)了多年的精心布置。It seemed as if she'd been gone forever. 好像她已經(jīng)永遠(yuǎn)地離開(kāi)了。He points two fingers at his head, as if he were holding a gun.A、if only 常表示愿望或一個(gè)未實(shí)現(xiàn)的條件，尤其用于感嘆句中。例如：If only he arrives in time!If only she would marry me!If only she had known about it!---->But she didn’t know.Only if a teacher has given permission is a student allowed to leave the room.學(xué)生只有得到老師的許可才能離開(kāi)教室。Only if the red light comes on is there any danger to employees.只有紅燈閃亮?xí)r才有危及職工的險(xiǎn)情。There are still a lot of ifs and buts before everything's settled.
本站僅提供存儲(chǔ)服務(wù)，所有內(nèi)容均由用戶發(fā)布，如發(fā)現(xiàn)有害或侵權(quán)內(nèi)容，請(qǐng)
點(diǎn)擊舉報(bào)。
