虛擬語氣用于條件狀語從句中
（1）表示與現(xiàn)在事實(shí)相反的假設(shè)，條件狀語從句中的謂語動(dòng)詞用“過去式（be動(dòng)詞的過去式用were）”，而主句中的謂語動(dòng)詞用“would / should/ could / might + 動(dòng)詞原形”。
如：
If I were a boy, I would join the army.
If the had time, she should go with you.

（2）表示與過去的事實(shí)相反，條件狀語從句中的謂語動(dòng)詞用過去完成時(shí)，主句中的謂語動(dòng)詞則用“would / should / might / could + have +過去分詞”。
如：
If he had taken my advice, he would have succeeded in the competition.

（3）表示與將來事實(shí)相反，條件狀語從句中的謂語動(dòng)詞一般過去時(shí)或should(were to) + 動(dòng)詞原形，而主句中的謂語動(dòng)詞則用would / should/could might + 動(dòng)詞原形。
如：
If it were to rain tomorrow, the football match would be put off.

（4）當(dāng)條件狀語從句表示的行為和主句表示的行為所發(fā)生的時(shí)間不一致時(shí)，動(dòng)詞的形式要根據(jù)它所表示的時(shí)間作相應(yīng)調(diào)整。
如：
If they had worked hard, they would be very tired.(從句說的是過去，主句指的是現(xiàn)在)

以下表格是虛擬語氣用于條件狀語從句中時(shí)，主句和從句謂語動(dòng)詞的形式：

	從句(if)	主句
與現(xiàn)在事實(shí)相反	主語+did/were	主語+ would/should/could/might + do
與過去事實(shí)相反	主語+ had done	主語+ should /would/could/might + have done
與將來事實(shí)相反	主語+ did/ should do/ were to do	主語+would/should/cold/might + do

有時(shí)侯在使用時(shí)可省略if,句子則可換成下列形式，即“were / had / should +主語”。
如：
Were I a boy, I would join the army.
Had he taken my advice, he would have succeeded.
Were it not for the expense, I would go to Britain.

虛擬語氣用于條件狀語從句中
（1）表示與現(xiàn)在事實(shí)相反的假設(shè)，條件狀語從句中的謂語動(dòng)詞用“過去式（be動(dòng)詞的過去式用were）”，而主句中的謂語動(dòng)詞用“would / should/ could / might + 動(dòng)詞原形”。
如：
If I were a boy, I would join the army.
If the had time, she should go with you.

（2）表示與過去的事實(shí)相反，條件狀語從句中的謂語動(dòng)詞用過去完成時(shí)，主句中的謂語動(dòng)詞則用“would / should / might / could + have +過去分詞”。
如：
If he had taken my advice, he would have succeeded in the competition.

（3）表示與將來事實(shí)相反，條件狀語從句中的謂語動(dòng)詞一般過去時(shí)或should(were to) + 動(dòng)詞原形，而主句中的謂語動(dòng)詞則用would / should/could might + 動(dòng)詞原形。
如：
If it were to rain tomorrow, the football match would be put off.

（4）當(dāng)條件狀語從句表示的行為和主句表示的行為所發(fā)生的時(shí)間不一致時(shí)，動(dòng)詞的形式要根據(jù)它所表示的時(shí)間作相應(yīng)調(diào)整。
如：
If they had worked hard, they would be very tired.(從句說的是過去，主句指的是現(xiàn)在)

以下表格是虛擬語氣用于條件狀語從句中時(shí)，主句和從句謂語動(dòng)詞的形式：

	從句(if)	主句
與現(xiàn)在事實(shí)相反	主語+did/were	主語+ would/should/could/might + do
與過去事實(shí)相反	主語+ had done	主語+ should /would/could/might + have done
與將來事實(shí)相反	主語+ did/ should do/ were to do	主語+would/should/cold/might + do

有時(shí)侯在使用時(shí)可省略if,句子則可換成下列形式，即“were / had / should +主語”。
如：
Were I a boy, I would join the army.
Had he taken my advice, he would have succeeded.
Were it not for the expense, I would go to Britain.