虚拟语气
(一)并不是if引导的条件从句都是虚拟语气。如果if从句所指的事很有可能发生，那么这是真实条件句；反之，则是虚拟条件句
A. If you study hard, you'll surely pass the examination. (真实条件句)
B. If I were a bird, I could fly freely in the sky. (虚拟条件句)
(二)虚拟语气中，有时条件从句和主句的时态可以不一致，这种句子叫做混合条件句，也叫错综时间条件句。这种句子的形式要根据表示的时间来调整
A. If it had not been for me, you would not be free.
B. If you had spoken to him yesterday, you would know what to do now.
C. “If I had missed, ”said William Tell, “and had shot too low, I was going to use this arrow on you. ”
(三)有时虚拟条件不用条件从句，而用介词短语来表示
A. They would not be able to live without him.
B. He would have failed but for his teacher's timely advice.
C. I had my hair cut off and sold it because I couldn't have lived through Christmas without giving you a present.
D. If only you had worked with greater care!
(四)假设的情况有时可以通过上下文或其他方式表现出来
A. He would have given you more help, but he was so busy.
B. I was ill that day. Otherwise I would have taken part in the parade.
C. He raised himself completely, obliging me to rise too, or I could not have supported him.
D. Einstein cared little for money, though he could have been very rich.
(五)如果条件从句的谓语动词含有连系动词were或助动词had或should, 可将if省略，而把were, had或should移到主语之前，构成倒装句形式
If they were here now, they could help us. (自然语序)
A.
Were they here now, they could help us. (倒装句)
If you had come earlier, you would have met him. (自然语序)
B.
Had you come earlier, you would have met him. (倒装句)
If he should join them in their discussion, they would be happy. (自然语序)
C.
Should he join them in their discussion, they would be happy. (倒装句)
The ship would have sunk with all on board if it had not been for the captain. (自然语序)
D.
The ship would have sunk with all on board had it not been for the captain. (倒装句)
(六)虚拟语气的一些其他用法
(1)在动词wish后的宾语从句中谓语动词用过去式，表示现在或将来的愿望；用过去完成式，表示过去的愿望。
A. I wish I knew the answer.
B. I wish that the time had not passed so fast!
(2)would rather后的从句中也用以上的结构。
A. I would rather they came tomorrow.
B. I would rather you had gone there too.
(3)由as if或as though引导的状语从句，也用以上的结构。
A. She loves the child as if he were her own.
B. “How wild his white hair looked-as if it had been electrified. ”
(4)在suggest, order, demand, propose, command, request, insist等后面的宾语从句，谓语动词用should+ 动词原形(should可省略)。
A. They requested that he (should) go at once.
B. He ordered that all (should) take part in the work.
(5)与下列词有关的表语从句、同位语从句也用以上的结构。
suggestion(proposal), order(decision), request(demand), plan, idea, a shame, a pity, no wonder
A. My idea is that we (should) win him over.
(6)在It is important(necessary, strange, natural, wonderful)that后以及It is suggested(requested, proposed, arranged, desired, ordered, insisted)that后从句中亦用以上的结构。
A. It is necessary that everyone should be there in time.
B. It is suggested that she should sing a song.
(7)在It is (high/about) time that从句中，谓语动词用一般过去式表示将来。
A. It is time we went to bed.
B. It's about time you began your work.
(8)由in order that, so that引导的状语从句用may或might加动词原形，而so that引导的状语从句也可用can或could加动词原形
A. The emperor ordered that the weavers should be given some gold in order that they might begin their work at once.
B. The teacher spoke slowly so that the students could(might)hear clearly.
(七)suggest表示“建议，提议”时，用虚拟语气；作“认为，提出，暗示，使人想起”时，用陈述语气
A. I suggest he (should) bring his friends in. (虚拟语气)
B. On the boy's pale face there was a half smile that seemed to suggest that he was happy to have given his life for his country. (陈述语气)
C. I suggest that you had an ulterior motive in doing this(陈述语气)
(八)insist表示“坚持要”或“一定要(某人做某事)”时，用虚拟语气；作“坚持认为，坚决主张、坚持说(某人的观点)”时，用陈述语气
A. They insisted that he (should) obey the rules. (虚拟语气)
B. She insisted that she needed no help. (陈述语气)
C. He insists that Shanghai is the largest city in China. (陈述语气)
(九)should have done表示应该做的事没做；shouldn't have done表示不该做的事做了；need have done表示必须做的事没做；needn't have done表示不必做的事做了。这些也都是虚拟语气
A. “It's our own fault, ”I thought bitterly. “We should have cut away the jungle brush. ”
B. How I regretted the hours wasted in the woods and fields, the days when I had played and should have studied!
C. You needn't have spent so much time on the problem; it is not worth doing at all.
责任编辑：李芳芳