1虚拟语气—时态退格
例：
If he were indoors，he wouldn't feel so cold.
他要是在室内就不会觉得冷了。
If anyone had been in his position，he would have done the same.
任何处在他位置的人都会这样做的。
If it were to rain tomorrow，I would stay at home.
明天万一下雨，我就待在家里了。
注：用with,without,under,but for等表示虚拟条件，并列连词or,otherwise含虚拟条件意义，
替换了if时候，也不要忘记，后方句子仍用虚拟。
注：在虚拟条件句中,如果出现有were,had,should,可以省去if,把这些词放在句子前面,构成虚拟倒装句。
Should he act like that again,he would be fined.
=If he should act like that again,he would be fined.
2虚拟语气—从句should省略
当主句谓语动词为表示愿望、建议、命令、要求等意义的特定标志词时,其宾语从句谓语动词要用（should）+动词原形的虚拟语气形式。
常见的此类标志词有：
一坚持（insist等）,
二命令（command,order等）,
三建议（advise, suggest,propose等）,
四要求（demand,require,request,ask等）。
另外像decide,desire,intend,recommend等也有这类虚拟用法。
例
Mother insists that the seats（should）be booked in advance.
妈妈坚持要预订座位。
注：当suggest意为“表明,暗示,说明”;insist意为“坚持说,坚持认为”时,从句谓语动词用陈述语气。
3特殊句式
•wish后的宾语从句谓语动词也用虚拟语气形式,表示与事实相反的一种愿望。（时态退格即可）
•would rather,would prefer等表示希望或婉转责备的动词后的宾语从句要用虚拟语气形式：用过去时表示与现在或将来事实相反的情况;用过去完成时表示与过去事实相反的情况。
•在以as if,as though引导的方式状语从句（如果主句的谓语动词是连系动词,
如be,feel,look,seem,sound等,那么as if,as though引导的就是表语从句）中,当表示非真实情况时,用虚拟语气,与wish后宾语从句谓语动词形式相同。（与现在相反,用一般过去时,be动词多用were;与过去事实相反,用had+过去分词;与将来可能相反,用would/could/might+动词原形。）
例：
She sings as if she were a singer.
她唱起歌来就像一位音乐家似的。（与现在事实相反）
注：当as if引导的从句表示真实情况时,就用陈述语气。
It looks as if it is going to rain.看上去天好像要下雨。
•由even if,even though引导的让步状语从句中,表示与所发生的事实相反时,应用虚拟语气,其构成形式与条件句中虚拟语气的构成形式相同。
例
Even though I had been with you then,I could not have done much for you.
即使当时我跟你在一起，也不能为你做更多的事情。（与过去相反）
注：如果even if,even though表示的是真实情况就用陈述语气。
Even if it rains,I will go.即使天下雨，我也要去。
•If only引起的感叹句
相当于How I wish +宾语从句,意思是“但愿……;要是……就好了”,用法和wish基本相同,可表示对现在、过去和将来的虚拟,比wish具有更强烈的感情色彩。
If only he could come!（对将来的虚拟）
他要是能来就好了!
•要不是…If it were not for...（= were it not for...）
If it hadn't been for...（= had it not been for...）“要不是因为有……;如果不是……”
例
If it hadn't been for the determined captain,all the passengers on board wouldn't have been saved.
要不是船长的意志坚定，船上的旅客就不会得救。
•It is（high/about）time that +从句,从句谓语动词为过去式或should+动词原形（should通常不省略）“……早就该……”
例
I think it is high time that she made up her mind.
我想她该拿定主意了。
•would rather sb.did sth.
would rather后接从句,表示“宁愿某人做某事”,从句谓语动词用过去时表示现在或将来的事情。
例
I would rather he were not present at the meeting tomorrow.
我倒希望他明天不要出席那个会议。
would rather sb.had done sth.
would rather后接从句,表示“宁愿某人已经做过某事（但实际上没有做）”,从句谓语动词用过去完成时表示过去的事情。
例
He would rather his son had agreed to take over his business.
他希望他的儿子答应接管他的生意。