虛擬語氣，要根據不同情況，用詞不同。這也是虛擬語氣不好記的原因。
1.表示與現在事實相反的情況：
從句：If主語+過去時
主句：
主語+should/would/could/might+do
例句:
If I were you , I would take an umbrella . 如果我是你，我會帶把傘。（事實：我不可能是你）
If I knew his telephone number, I would tell you.
如果我知道他的電話號碼，我就會告訴你。（事實：不知道）
If there were no air or water, there would be no living things on the earth.
如果沒有水和空氣，地球上就不會有生物。（事實：地球上既有空氣也有水）
If I had any money with me, I could lend you some. 如果我帶錢了，我就會借給你些。（事實：沒帶錢）
If he studied harder, he might pass the exam. 如果他再努力些，就能透過考試了。（事實：沒有努力）
she looked at me as if I had been a stranger. 她看我的樣子好像我是一個陌生人。（事實：我並非陌生人）
2.表示與過去事實相反的情況
從句：If主語+had+done
主語+should/would/could/might+have done
If I had got there earlier, I should/could have met her.
如果我早到那兒，我就會見到她。（事實：去晚了）
2. If he had taken my advice, he would not have made such a mistake.
如果他聽我的勸告的話，就不會犯這樣的錯誤了。（事實：沒有聽我的話）
3.表示對將來情況的主觀推測
從句：if+主語+were to do
If he should come here tomorrow, I would talk to him.
如果他明天來這兒的話，我就跟他談談。（事實：來的可能性很小）
If there were a heavy snow next Sunday, we would not go skating.
如果下週日下大雪，我們就不能去滑冰了。（事實：不知能否下雪）
If she were to be here next Monday, I would tell her about the matter.
如果她下週一來這兒的話，我就會告訴她這件事。
虛擬語氣，要根據不同情況，用詞不同。這也是虛擬語氣不好記的原因。
1.表示與現在事實相反的情況：
從句：If主語+過去時
主句：
主語+should/would/could/might+do
例句:
If I were you , I would take an umbrella . 如果我是你，我會帶把傘。（事實：我不可能是你）
If I knew his telephone number, I would tell you.
如果我知道他的電話號碼，我就會告訴你。（事實：不知道）
If there were no air or water, there would be no living things on the earth.
如果沒有水和空氣，地球上就不會有生物。（事實：地球上既有空氣也有水）
If I had any money with me, I could lend you some. 如果我帶錢了，我就會借給你些。（事實：沒帶錢）
If he studied harder, he might pass the exam. 如果他再努力些，就能透過考試了。（事實：沒有努力）
she looked at me as if I had been a stranger. 她看我的樣子好像我是一個陌生人。（事實：我並非陌生人）
2.表示與過去事實相反的情況
從句：If主語+had+done
主句：
主語+should/would/could/might+have done
例句:
If I had got there earlier, I should/could have met her.
如果我早到那兒，我就會見到她。（事實：去晚了）
2. If he had taken my advice, he would not have made such a mistake.
如果他聽我的勸告的話，就不會犯這樣的錯誤了。（事實：沒有聽我的話）
3.表示對將來情況的主觀推測
從句：if+主語+were to do
主句：
主語+should/would/could/might+do
例句:
If he should come here tomorrow, I would talk to him.
如果他明天來這兒的話，我就跟他談談。（事實：來的可能性很小）
If there were a heavy snow next Sunday, we would not go skating.
如果下週日下大雪，我們就不能去滑冰了。（事實：不知能否下雪）
If she were to be here next Monday, I would tell her about the matter.
如果她下週一來這兒的話，我就會告訴她這件事。