发布时间：2016-03-18 来源：新东方在线 发布人：zolo
1) 表示与现在情况相反：主句谓语用“would / could / might 动词原形”，从句谓语用“动词的一般过去时”(动词be的过去式一律用were)。
If I were you, I would not accept his offer.
If I had time, I would certainly go to the cinema with you.
2) 表示与过去情况相反：主句谓语用“would / could / might have 过去分词”，从句谓语用过去完成时。
If I had got up a little earlier, I wouldn’t have missed the train.
If I had been more careful, I might have passed that exam.
3) 表示与将来情况相反：主句谓语用“would / could / might 动词原形”，从句谓语用“were 动词不定式”或“should 动词原形”。
If I were to do the job, I would not be able to have enough time to study.
If it should rain tomorrow, I would not go out with you.
如果虚拟条件句的从句中含有were, had, should, could等词时，可以省略连接词if，但这时必须把were, had, should, could等词移到主语前面，形成倒装。这种句型主要用于书面形式。
Were I to do the job, I would finish doing it within two weeks.
Had it not been for his help, we couldn’t have arrived there on time.
Should it rain tomorrow, I would stay at home.
I wish I had enough money to buy a car.
I wish I were as young and energetic as you.
2) 表示过去未能实现的愿望，宾语从句中的谓语动词用过去完成时(had 过去分词)或“would / could have 过去分词 ”。
I wish I hadn’t made such a mistake.
I wish I could have done it better.
3) 表示将来不可能实现的愿望，宾语从句中的谓语动词用“would / should (could, might) 动词原形”。
I wish I would not get old.
I wish I could travel around the world one day.
在一些动词后面的宾语从句中，谓语动词要用虚拟语气。这时，谓语动词用动词原形或should 动词原形。这类动词一般表示命令，要求，决定，建议，主张等概念，主要有：advise, ask, command, decide, demand, desire, direct, insist, move, order, propose, recommend, request, require, suggest,等。
The workers demanded that their wages (should) be raised by 10 per cent.
The teacher decided that you do the experiment first.
在一些名词后面的表语从句和同位语从句中，谓语动词要用虚拟语气。这时，谓语动词用动词原形或should 动词原形。这类名词一般表示命令，要求，决定，建议，主张等概念，主要有：advice, idea, instruction, motion, order, plan, proposal, recommendation, request, requirement, suggestion,等。
My suggestion is that we (should) send for a doctor immediately.
He gave the order that they (should) do the experiment again.
If the weather had been more favourable, the crops would be growing still better.