虛擬語氣(Subjunctive Mood)這一語法項目是各類英語考試中心測試的重點之一。虛擬語氣是一種特殊的動詞形式，用來表示說話人所說的話并不是事實，而是一種假設、愿望、懷疑或推測。判斷是真實條件句還是非真實條件句。只有在非真實條件句中才使用虛擬語氣。通過句子意思，看假設的條件是否能夠實現，能夠實現是真實條件句，不能使用虛擬語氣；假設的條件不能實現則是非真實條件句，要用虛擬語氣.判斷這個假設是與哪個事實相反。通常有三種情況：①與過去事實相反。②與現在事實相反。③與將來事實可能相反
I: 最基本的虛擬語氣句型:
1. 虛擬現在時表示與現在事實相反的假設，其if 從句的謂語形式用動詞的過去式(be 一般用were)，主句用would/ should/ could/ might 動詞原形。If places were a like, there would be little need for geographers.如果各個地方都一樣，就不需要地理學家了。
2. 虛擬過去時是表示與過去事實相反的假設，if 從句的謂語形式用過去完成時即had＋過去分詞，主句用would / should / could / might have 過去分詞。If he had known your address yesterday,he would have telephoned you.
3. 虛擬將來時是表示對將來實現的可能性很小的或不確定的假設。If從句的謂語形式用一般過去式或用were to / should 動詞原形，主句用would / should/could/ might 動詞原形。If he were to leave today, he would get there by Friday
4. 省略if 采用倒裝語序的條件句。有時可以把含有助動詞、情態動詞、be或have的虛擬條件句中的連詞if省去，而將had , should, were 等詞提到主語之前，即用倒裝結構。Had he worked harder, he would have got through the exams.Were he to leave today, he would get there by Friday.Were I in your place, I wouldn’t do that.

本文來自：逍遙右腦記憶 /waiyu/yingyuxuexi/18251.html

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