我們知道由if 引導(dǎo)的條件句有兩種形式，一種是真實(shí)的條件句，也就說(shuō)是某事很可能發(fā)生，條件是可能存在的，主句中某種情況發(fā)生的概率也是非常高的。例如If you intend using humor in your talk to make people smile, you must know how to identify shared experiences and problems.(2002。Text1 )(如果你想在談話中用幽默來(lái)使人發(fā)笑，你就必須知道如何識(shí)別共同的經(jīng)歷和共同的問(wèn)題。)

另一種就非真實(shí)條件句，通過(guò)虛擬語(yǔ)氣來(lái)表達(dá)。例如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。)在這句話中，假設(shè)“不堵塞”，但是真實(shí)情況并不是這樣，所以用虛擬語(yǔ)氣。一般有6種常見(jiàn)的形式：

1)與現(xiàn)在事實(shí)相反的非真實(shí)條件句，從句中用一般過(guò)去時(shí)，主句中用would/could/ should 加動(dòng)詞原形，be 動(dòng)詞的過(guò)去式為were.

If you then examined the European national youth teams that feed the World Cup and professional ranks, you would find this strange phenomenon to be ever more pronounced.(2007,text 1 )(查看為世界杯和專業(yè)隊(duì)輸送人才的歐洲國(guó)家青年隊(duì)，你會(huì)發(fā)現(xiàn)這一奇怪的現(xiàn)象更加明顯。)

2)與過(guò)去事實(shí)相反的非真實(shí)條件句，從句用過(guò)去完成時(shí)，主句用would/could/should +have done .

If he had played last season,however,he would have been one of 42. (2008 text3 )(如果他打了上個(gè)賽季，他將只是42個(gè)(最高的人)中的一個(gè))

3)與將來(lái)事實(shí)相反的非真實(shí)條件句，從句用should do 或 were to do 結(jié)構(gòu)，主句中用 would /could/should 加動(dòng)詞原形。

If you were to examine the birth certificates of every soccer player in 2006’s World Cup tournament, you would most likely find a noteworthy quirk: elite soccer players are more likely to have been born in the earlier months of the year than in the later months.(2007 text 1)(如果查看2006年世界杯聯(lián)賽每個(gè)足球運(yùn)動(dòng)員的出生證，你很可能發(fā)笑一個(gè)值得注意的奇怪現(xiàn)象：好的足球運(yùn)動(dòng)員都在一年的頭幾個(gè)月而不是后幾個(gè)月出生。)

4)混合時(shí)態(tài)的虛擬。指的是主句和從句分別表示兩個(gè)時(shí)態(tài)，動(dòng)詞形式依照上述三種形式進(jìn)行相應(yīng)的變化。

If he had put all the important files in the safe yesterday, his boss wouldn’t be scolding him so angrily now.(如果昨天他把所有重要文件都放在保險(xiǎn)箱中，他的老板現(xiàn)在也不會(huì)這個(gè)嚴(yán)厲的說(shuō)他。)

5)省if將從句中的系動(dòng)詞或助動(dòng)詞提前到主語(yǔ)之前，變成倒裝句，考生對(duì)這種形式應(yīng)該理解和掌握。

Had it not for the timely investment from the general public, our company would not be so thriving as it is.(1998 )(如果不是群眾投資，我們的公司不會(huì)像現(xiàn)在這么興旺。)

6)用介詞或連詞表示虛擬.比如with,without, under…condition, but for. 　　

And if one received a grape without having to provide her token in exchange at all, the other either tossed her own token at the researcher or out of the chamber, or refused to accept the slice of cucumber.(2005 text 1 )(如果一只猴子甚至沒(méi)有用石塊就能得到葡萄，另一只猴子就會(huì)向研究人員扔石頭，或者把石頭扔出房間，或者拒絕接受一片黃瓜。)

這是比較常規(guī)和比較容易辨識(shí)的虛擬語(yǔ)氣，希望同學(xué)們多加練習(xí)。希望廣大的考生在復(fù)習(xí)的過(guò)程中把遇到的所有長(zhǎng)難句都匯總到一個(gè)筆記本上，積累自己的薄弱點(diǎn)，才能針對(duì)性提高。預(yù)?？忌鷤兌寄芸荚図樌?。