--Galileo proved that the earth revolves round the sun.

　　--The teacher told the students that knowledge is power.

　　如果從句中有一個表示絕對過去時間的狀語，就不必把一般過去時變為過去完成時。

　　--He said that he joined the Red Army in 1933.

　　虛擬語氣

　　1. 表示現在/過去/將來情況的虛擬條件句

　　虛擬條件句主要有三種結構：

　　1)　表示與現在情況相反：主句謂語用“would / could / might +動詞原形”，從句謂語用“動詞的一般過去時”(動詞be的過去式一律用were)。

　　If I were you, I would not accept his offer.

　　If I had time, I would certainly go to the cinema with you.

　　2) 表示與過去情況相反：主句謂語用“would / could / might + have +過去分詞”，從句謂語用過去完成時。

　　If I had got up a little earlier, I wouldn’t have missed the train.

　　If I had been more careful, I might have passed that exam.

　　3) 表示與將來情況相反：主句謂語用“would / could / might +動詞原形”，從句謂語用“were +動詞不定式”或“should +動詞原形”。

　　If I were to do the job, I would not be able to have enough time to study.

　　If it should rain tomorrow, I would not go out with you.

　　2. 虛擬條件句連接詞if的省略

　　如果虛擬條件句的從句中含有were, had, should, could等詞時，可以省略連接詞if，但這時必須把were, had, should, could等詞移到主語前面，形成倒裝。這種句型主要用于書面形式。

　　Were I to do the job, I would finish doing it within two weeks.

　　Had it not been for his help, we couldn’t have arrived there on time.

　　Should it rain tomorrow, I would stay at home.

　　3. wish后賓語從句中的謂語構成

　　動詞wish后的賓語從句表示未實現的或不可能實現的愿望，其賓語從句中的謂語動詞要用虛擬語氣，有以下三種構成形式。

　　1) 表示現在不可能實現的愿望，賓語從句中的謂語動詞用一般過去時。(be的過去式為were)。

　　I wish I had enough money to buy a car.

　　I wish I were as young and energetic as you.

　　2) 表示過去未能實現的愿望，賓語從句中的謂語動詞用過去完成時(had +過去分詞)或“would / could + have +過去分詞 ”。

　　I wish I hadn’t made such a mistake.

　　I wish I could have done it better.

　　3) 表示將來不可能實現的愿望，賓語從句中的謂語動詞用“would / should (could, might) +動詞原形”。

　　I wish I would not get old.

　　I wish I could travel around the world one day.

　　4. 某些動詞后的賓語從句中謂語動詞要用虛擬語氣

　　在一些動詞后面的賓語從句中，謂語動詞要用虛擬語氣。這時，謂語動詞用動詞原形或should +動詞原形。這類動詞一般表示命令，要求，決定，建議，主張等概念，主要有：advise, ask, command, decide, demand, desire, direct, insist, move, order, propose, recommend, request, require, suggest,等。

　　The workers demanded that their wages (should) be raised by 10 per cent.

　　The teacher decided that you do the experiment first.

　　5. 某些名詞后的表語從句和同位語從句中謂語動詞要用虛擬語氣

　　在一些名詞后面的表語從句和同位語從句中，謂語動詞要用虛擬語氣。這時，謂語動詞用動詞原形或should +動詞原形。這類名詞一般表示命令，要求，決定，建議，主張等概念，主要有：advice, idea, instruction, motion, order, plan, proposal, recommendation, request, requirement, suggestion,等。

　　My suggestion is that we (should) send for a doctor immediately.

　　He gave the order that they (should) do the experiment again.