一、對現在情況的虛擬 條件從句中謂語動詞用一般過去式，主句用“would/should/might/could+動詞原形”形式，表示對現在不可能實現情況的假想。 If I were you,I would choose to work in a small town. 如果我是你，我會選擇在小城鎮工作。（事實上我不是你） If I had a map now,we could easily get out of the forest. 如果現在有地圖，我們能很容易地走出森林。（事實上是現在沒有地圖） 注意：在條件從句中，如果謂語動詞是be的形式，不管主語是單數還是複數，書面語中用were,而口語中如果是單數，也可以用was,不過在if I were...中一般用were. If the world were perfect,how could we enjoy the pleasure and comfort of being successful? 世界若完美，我們如何能嚐到創造成功的快慰？ 二、對過去情況的虛擬 條件從句中謂語動詞用過去完成式，主語用“would/could/should/might+have+動詞的過去分詞”形式。 If it had not been for your help yesterday,I could not have caught the bus. 如果昨天沒有你的幫助，我不會趕上公交車。（事實是你昨天已經幫助了我，所以我趕上了車) 三、對將來情況的虛擬 在表示與將來事實相反的條件從句中，謂語動詞可用should do,were to do或動詞的過去式三種形式表示，但意義略有不同。should表示的可能性最大，動詞過去式的可能性次之，were to do 的可能性最小。 If things were to be twice，all would be wise. 假如凡事都可以重新做一次，人人皆可成為聰明人。（事實是並不是所有的事都可以重新做一次)。

If you come to my house.If you will come to my house.If you are going to my house.這三個是if的條件狀語，主語用將來時態從句If you come to my house.是用一般時態表將來。If you will come to my house就是直接用一般將來時態If you are going to my house.進行時態表將來