虛擬語氣被普遍認(rèn)為是難度大，不易掌握的語法項(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)虛擬語氣的謂語動(dòng)詞變化，把虛擬語氣分為四大類型，以便掌握。
l. 時(shí)間選擇型
當(dāng)虛擬語氣用來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、將來和過去情況相反的三種不同時(shí)間，從而決定謂語動(dòng)詞。這類虛擬語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．（與將來情況相反）
I wouldn't have finished the work without your help． （與過去情況相反）
（2）由 even if (though) 引導(dǎo)的讓步狀語從句，其謂語動(dòng)詞變化同于虛擬條件句，在口語中也可用直陳語氣。
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．（與過去情況相反）
（3） wish后的賓語從句
I wish I were five years younger than you．（與現(xiàn)在情況相反）
He wishes you would go with him.（與將來情況相反）
I wished I had won the match．（與過去情況相反）
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)的表語從句和方式狀語從句
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
這種類型的虛擬語氣一般用于主語從句、賓語從句、表語和同位語從句。謂語由should+動(dòng)詞原形構(gòu)成，無論什么人稱都不能用 would, should在口語中可以略去。
（1）在主語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、建議一類動(dòng)詞后的賓語從句，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)生過的事物的看法，或當(dāng)suggest為“說明了”，“
l. 時(shí)間選擇型
當(dāng)虛擬語氣用來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、將來和過去情況相反的三種不同時(shí)間，從而決定謂語動(dòng)詞。這類虛擬語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．（與將來情況相反）
I wouldn't have finished the work without your help． （與過去情況相反）
（2）由 even if (though) 引導(dǎo)的讓步狀語從句，其謂語動(dòng)詞變化同于虛擬條件句，在口語中也可用直陳語氣。
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．（與過去情況相反）
（3） wish后的賓語從句
I wish I were five years younger than you．（與現(xiàn)在情況相反）
He wishes you would go with him.（與將來情況相反）
I wished I had won the match．（與過去情況相反）
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)的表語從句和方式狀語從句
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
這種類型的虛擬語氣一般用于主語從句、賓語從句、表語和同位語從句。謂語由should+動(dòng)詞原形構(gòu)成，無論什么人稱都不能用 would, should在口語中可以略去。
（1）在主語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、建議一類動(dòng)詞后的賓語從句，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)生過的事物的看法，或當(dāng)suggest為“說明了”，“