1)与现在事实相反的非真实条件句，从句中用一般过去时，主句中用would/could/ should 加动词原形，be 动词的过去式为were.
If you then examined the European national youth teams that feed the World Cup and professional ranks, you would find this strange phenomenon to be ever more pronounced.(2007,text 1 )(查看为世界杯和专业队输送人才的欧洲国家青年队，你会发现这一奇怪的现象更加明显。)
2)与过去事实相反的非真实条件句，从句用过去完成时，主句用would/could/should +have done .
If he had played last season,however,he would have been one of 42. (2008 text3 )(如果他打了上个赛季，他将只是42个(最高的人)中的一个)
3)与将来事实相反的非真实条件句，从句用should do 或 were to do 结构，主句中用 would /could/should 加动词原形。
If you were to examine the birth certificates of every soccer player in 2006’s World Cup tournament, you would most likely find a noteworthy quirk: elite soccer players are more likely to have been born in the earlier months of the year than in the later months.(2007 text 1)(如果查看2006年世界杯联赛每个足球运动员的出生证，你很可能发笑一个值得注意的奇怪现象：好的足球运动员都在一年的头几个月而不是后几个月出生。)
If he had put all the important files in the safe yesterday, his boss wouldn’t be scolding him so angrily now.(如果昨天他把所有重要文件都放在保险箱中，他的老板现在也不会这个严厉的说他。)
Had it not for the timely investment from the general public, our company would not be so thriving as it is.(1998 )(如果不是群众投资，我们的公司不会像现在这么兴旺。)
6)用介词或连词表示虚拟.比如with,without, under…condition, but for.
And if one received a grape without having to provide her token in exchange at all, the other either tossed her own token at the researcher or out of the chamber, or refused to accept the slice of cucumber.(2005 text 1 )(如果一只猴子甚至没有用石块就能得到葡萄，另一只猴子就会向研究人员扔石头，或者把石头扔出房间，或者拒绝接受一片黄瓜。)