1、表示与现在事实相反的情况:
从句:If+主语+过去时(Be动词用were)
主句:主语+ should/would+do:
1.If I were you,I would take an umbrella.
如果我是你,我会带把伞。(事实:我不可能是你)
2、表示与过去事实相反的情况
从句:If+主语+had+done
主句:主语+should/would+have done
eg:1. If I had gotten there earlier,I should/would have met her.
如果我早到那儿,我就会见到她。(事实:去晚了)
3、表示对将来情况的主观推测
从句:①if+主语+were to do (if 表示未来的虚拟语气独有该形式,其他如wish, even
if等词都没有该形式来表示未来的虚拟语气)
②if+主语+should+do
③if+主语+过去式(be动词用were)
主句:主语+should/would+do
eg:1.If he should come here tomorrow,I would talk to him.
如果他明天来这儿的话,我就跟他谈谈。(事实:来的可能性很小,不可能)
当虚拟条件句的谓语动词含有were,should,had时,if可以省略,这时条件从句要用倒装语序,即把were,should,had等词置于句首,这种多用于书面语。
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