1、 虚拟现在：If +P.,should(would,could,might)+V

　　If peoplel all lived a hundred years or more, the earth would be too small for them.

　　If I were a student of Russia, I could read the novels by Tolstoy.

　　2、 虚拟过去：If+had +p.p, should(would,could,might)+have+p.p

　　If I had not watched TV last night, I could have finished my homework.

　　If it hadn’t rained last Sunday, we might have gone picnicing.

　　3、 虚拟将来：If+should+V，should/would+V

　　If +P.，should/would+V

　　If were to+V, could/would+V

　　If it should rain tomorrow, our picnic would be put off.

　　If it rained tomorrow, our picnic would be put off.

　　If it were to rain tomorrow, our picnic would be put off.

　　注意：无论第几人称，be动词只能用were

　　should 只用于第一人称，would用于任何人称

　　4、 wish引起的虚拟：“但愿”，表示主观愿望与现实差距较大

　　Children wish every day were a New Year’s Day.

　　I wish I could be the Beenthoven of China some day.

　　I wish he would be more careful.

　　(would,should,could,might可表将来)

　　判断：从句动作和wish同时发生，从句用过去时

　　从句动作在wish前发生，从句用过完

　　从名动作在wish后发生，从句用情态动词过去式+V，虚拟将来

　　5、 would rather 引起的从句表虚拟：“宁愿”，“真希望”(原则同wish)

　　I would rather she were not there.

　　I would rather I had done the word for him.

　　6、without, but for“要不是”，其功能相当于一个虚拟条件句。后面主句用虚拟语气

　　Without(but for)your help, I might not be find my way home.

　　6、 should+V跟在下列词后，表“应该…”，should常省去

　　suggest,insist,propose,demand,ask,require,order…(这些词变成名词，规则照旧)

　　The doctor insists that his patient(should)not go to bed later than 10.

　　My proposal is that some comrades(should)be sent to help them.(名词)

　　7、 It is (was)+necessary,(important,possible,impossible,imperative)+that+should do

　　8、 It is(was) time (that)+should do/一般过去时(注意：should不可省)

　　It time we shuld get up =It is time we got up.

　　It is high time our athletes showed theirbest.=It is hight time our athletes should show their best