虚拟语气的用法和时态是什么？

退时态：真实语气中的现在时变成过去时，过去时变成过去完成时，将来时变成过去将来时
1．条件句中：
 If it were not for…；If it hadn’t been for…这两种句型表示“要是没有”，相当于but for
If it had not been for the PLA man, he would not be studying English now.
 if…only…（或If only…）表示“要是…就好了”
1．名词性从句：
 demand/suugest/order/insist/propose/request/ask/advise/prefer/command/desire that…
They demanded that the aggressor troops (should) be withdrawn immediately.
由insist引导的宾语从句可以虚拟也可以不虚拟：
He insisted that he was right.坚持认为
He insisted that we should agree with him.坚持某事
由suggest引导的宾语从句可以虚拟也可以不虚拟：
His white face suggests that his not healthy.表明
He suggested that we have a rest.建议

If I could only see him once!
If only I had listened to your advice. 很明显，这种句型省略了主句
2．其他状语从句中：
 as if/as though/even if…
Tom looked sad as if he had heard bad news.
I won’t lend you any money even I had money.
3．名词性从句：
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