虛擬語(yǔ)氣被普遍認(rèn)為是難度大，不易掌握的語(yǔ)法項(xiàng)目，很容易使人望而生畏，能否從中找出一些規(guī)律呢？下面就是根據(jù)虛擬語(yǔ)氣的謂語(yǔ)動(dòng)詞變化，把虛擬語(yǔ)氣分為四大類(lèi)型，以便掌握。
l. 時(shí)間選擇型
當(dāng)虛擬語(yǔ)氣用來(lái)表示一種不能成為現(xiàn)實(shí)、不真實(shí)的情況時(shí)，須選擇與現(xiàn)在、將來(lái)和過(guò)去情況相反的三種不同時(shí)間，從而決定謂語(yǔ)動(dòng)詞。這類(lèi)虛擬語(yǔ)氣主要用于如下幾方面:
（1）虛擬條件句（含蓄虛擬條件句）
If l were you, l would study much harder．（與現(xiàn)在情況相反）
If he did（were to do，should do）it，he would do it well．（與將來(lái)情況相反）
I wouldn't have finished the work without your help． （與過(guò)去情況相反）
（2）由 even if (though) 引導(dǎo)的讓步狀語(yǔ)從句，其謂語(yǔ)動(dòng)詞變化同于虛擬條件句，在口語(yǔ)中也可用直陳語(yǔ)氣。
Even if he were here, he wouldn't be able to help you． （與現(xiàn)在情況相反）
Nothing could have saved your father，even if the doctor had arrived on time．（與過(guò)去情況相反）
（3） wish后的賓語(yǔ)從句
I wish I were five years younger than you．（與現(xiàn)在情況相反）
He wishes you would go with him.（與將來(lái)情況相反）
I wished I had won the match．（與過(guò)去情況相反）
注意：wish的時(shí)態(tài)不影響從句三種時(shí)間的判定。
（4） as if (though)引導(dǎo)的表語(yǔ)從句和方式狀語(yǔ)從句
He looks as if he were very sleepy．（與現(xiàn)在情況相反）
They are talking about something, as if they were quarrelling with each other．
2．should+動(dòng)詞原形型
這種類(lèi)型的虛擬語(yǔ)氣一般用于主語(yǔ)從句、賓語(yǔ)從句、表語(yǔ)和同位語(yǔ)從句。謂語(yǔ)由should+動(dòng)詞原形構(gòu)成，無(wú)論什么人稱(chēng)都不能用 would, should在口語(yǔ)中可以略去。
（1）在主語(yǔ)從句中用以表示驚奇、惋惜、理應(yīng)如此，構(gòu)成 It is natural （important, necessary, strange, a pity, a shame等）that… 句型。
It is natural that you should say apology to him．
It is a pity that you should be careless．
（2）用于表示命令、建議一類(lèi)動(dòng)詞后的賓語(yǔ)從句，如：suggest，move，insist，demand，request，command等。
The young man insisted that he should be sent to do the work．
I suggested that we should set off earlier．
應(yīng)注意：當(dāng)insist表示對(duì)已發(fā)生過(guò)的事物的看法，或當(dāng)suggest為“說(shuō)明了”，“
l. 時(shí)間選擇型
當(dāng)虛擬語(yǔ)氣用來(lái)表示一種不能成為現(xiàn)實(shí)、不真實(shí)的情況時(shí)，須選擇與現(xiàn)在、將來(lái)和過(guò)去情況相反的三種不同時(shí)間，從而決定謂語(yǔ)動(dòng)詞。這類(lèi)虛擬語(yǔ)氣主要用于如下幾方面:
（1）虛擬條件句（含蓄虛擬條件句）
If l were you, l would study much harder．（與現(xiàn)在情況相反）
If he did（were to do，should do）it，he would do it well．（與將來(lái)情況相反）
I wouldn't have finished the work without your help． （與過(guò)去情況相反）
（2）由 even if (though) 引導(dǎo)的讓步狀語(yǔ)從句，其謂語(yǔ)動(dòng)詞變化同于虛擬條件句，在口語(yǔ)中也可用直陳語(yǔ)氣。
Even if he were here, he wouldn't be able to help you． （與現(xiàn)在情況相反）
Nothing could have saved your father，even if the doctor had arrived on time．（與過(guò)去情況相反）
（3） wish后的賓語(yǔ)從句
I wish I were five years younger than you．（與現(xiàn)在情況相反）
He wishes you would go with him.（與將來(lái)情況相反）
I wished I had won the match．（與過(guò)去情況相反）
注意：wish的時(shí)態(tài)不影響從句三種時(shí)間的判定。
（4） as if (though)引導(dǎo)的表語(yǔ)從句和方式狀語(yǔ)從句
He looks as if he were very sleepy．（與現(xiàn)在情況相反）
They are talking about something, as if they were quarrelling with each other．
2．should+動(dòng)詞原形型
這種類(lèi)型的虛擬語(yǔ)氣一般用于主語(yǔ)從句、賓語(yǔ)從句、表語(yǔ)和同位語(yǔ)從句。謂語(yǔ)由should+動(dòng)詞原形構(gòu)成，無(wú)論什么人稱(chēng)都不能用 would, should在口語(yǔ)中可以略去。
（1）在主語(yǔ)從句中用以表示驚奇、惋惜、理應(yīng)如此，構(gòu)成 It is natural （important, necessary, strange, a pity, a shame等）that… 句型。
It is natural that you should say apology to him．
It is a pity that you should be careless．
（2）用于表示命令、建議一類(lèi)動(dòng)詞后的賓語(yǔ)從句，如：suggest，move，insist，demand，request，command等。
The young man insisted that he should be sent to do the work．
I suggested that we should set off earlier．
應(yīng)注意：當(dāng)insist表示對(duì)已發(fā)生過(guò)的事物的看法，或當(dāng)suggest為“說(shuō)明了”，“