對(duì)過去事實(shí)的虛擬
基本形式：If + had done…，…would /could / should /might + have done
例如：If she had been warned earlier，she wouldn't have broken the rules.
（事實(shí)上：She was not warned earlier and she broke the rules.）
If it hadn't rained，the match would have seemed more fascinating.
（事實(shí)上：It rained and the match was less fascinating.）
此種虛擬可進(jìn)行倒裝，如：
Had the letter been sent out，it would have ruined our friendship.= If the letter had been sent out，it would have ruined our friendship.
對(duì)將來事實(shí)的虛擬基本形式：
If + should do…，…would /could /should /might + do；意思類似漢語中的“萬一”
例如：If he should forget the date，I might teach him a good lesson.
（事實(shí)上：他不大可能忘記那個(gè)日期）
If it should snow this afternoon，we could make a snowman.
（事實(shí)上不大可能會(huì)下雪）
此種虛擬可倒裝，如：Should my car fail，I would have to return home on foot.= If my car should fail，I would have to return home on foot.
注意1：部分動(dòng)詞的賓語從句中需用虛擬語氣，形式為should do，其中should常被省略。
此類動(dòng)詞有：insist，demand，suggest，propose，order，require，decide，ask，request等。
例句：We all insist that we （should） not rest until we finish the work.
The professor suggests that the students （should）collect enough mate rials before they work on this project.
上面的動(dòng)詞如果以名詞形式出現(xiàn)時(shí)，后面的that從句仍然要采用虛擬語氣。
He gives me the suggestion that I（should）eat breakfast every moning.
注意2：在一些慣用語之后經(jīng)常需要用虛擬，來表示與事實(shí)相反或者難以實(shí)現(xiàn)的事情這類習(xí)語有：as if ，as though，but for，otherwise，without，wish，if，only等。
例句： But for your help，I would not have arrived here in time.
（如果沒有你的幫助，我就不能準(zhǔn)時(shí)到達(dá)）
Without your help，I would not arrive here in time.
注意3：在下列形容詞引導(dǎo)的that從句中必須要用虛擬語氣（should）do，但是由于should經(jīng)常被省略，所以實(shí)際上用的就是動(dòng)詞原形。
這類形容詞有：It is important/ necessary/ proper/ imperative/ essential/advisable等+ that
例句：It is necessary that he（should）realize his situation.
基本形式：If + had done…，…would /could / should /might + have done
例如：If she had been warned earlier，she wouldn't have broken the rules.
（事實(shí)上：She was not warned earlier and she broke the rules.）
If it hadn't rained，the match would have seemed more fascinating.
（事實(shí)上：It rained and the match was less fascinating.）
此種虛擬可進(jìn)行倒裝，如：
Had the letter been sent out，it would have ruined our friendship.= If the letter had been sent out，it would have ruined our friendship.
對(duì)將來事實(shí)的虛擬基本形式：
If + should do…，…would /could /should /might + do；意思類似漢語中的“萬一”
例如：If he should forget the date，I might teach him a good lesson.
（事實(shí)上：他不大可能忘記那個(gè)日期）
If it should snow this afternoon，we could make a snowman.
（事實(shí)上不大可能會(huì)下雪）
此種虛擬可倒裝，如：Should my car fail，I would have to return home on foot.= If my car should fail，I would have to return home on foot.
注意1：部分動(dòng)詞的賓語從句中需用虛擬語氣，形式為should do，其中should常被省略。
此類動(dòng)詞有：insist，demand，suggest，propose，order，require，decide，ask，request等。
例句：We all insist that we （should） not rest until we finish the work.
The professor suggests that the students （should）collect enough mate rials before they work on this project.
上面的動(dòng)詞如果以名詞形式出現(xiàn)時(shí)，后面的that從句仍然要采用虛擬語氣。
He gives me the suggestion that I（should）eat breakfast every moning.
注意2：在一些慣用語之后經(jīng)常需要用虛擬，來表示與事實(shí)相反或者難以實(shí)現(xiàn)的事情這類習(xí)語有：as if ，as though，but for，otherwise，without，wish，if，only等。
例句： But for your help，I would not have arrived here in time.
（如果沒有你的幫助，我就不能準(zhǔn)時(shí)到達(dá)）
Without your help，I would not arrive here in time.
注意3：在下列形容詞引導(dǎo)的that從句中必須要用虛擬語氣（should）do，但是由于should經(jīng)常被省略，所以實(shí)際上用的就是動(dòng)詞原形。
這類形容詞有：It is important/ necessary/ proper/ imperative/ essential/advisable等+ that
例句：It is necessary that he（should）realize his situation.