1.基礎If I _____ you, I would talk to the teacher about the problem right away.
測驗重點：與現在事實相反
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正確答案：(C) were
與現在事實相反的假設，if 子句用過去式且 be 動詞一律用 were（不分人稱）：If I were you。這是假設語氣的招牌句型；had been 是與「過去」相反，本句語境是現在的建議。
內容概述
假設語氣以「時態退位」表達與事實相反：①與現在事實相反——If + S + 過去式（be 動詞用 were）, S + would/could + 原形（If I were you, I would apologize.）②與過去事實相反——If + S + had p.p., S + would have p.p.（If you had studied harder, you would have passed.）③混合時間——過去的假設影響現在：If + had p.p., ... would + 原形 + now。相關句型：I wish + 過去式／had p.p.（但願）、as if（彷彿）、without／but for＝if it were not for／if it had not been for（若非）、It's time + S + 過去式。倒裝假設（Were I you... / Had I known...）將 if 省略。假設語氣是學測文法與翻譯的必考重點。
學習重點
- 1與現在相反：If + 過去式（were）, would/could/might + V——時態「退一步」表示非事實
- 2與過去相反：If + had p.p., would have p.p.——兩邊都退到「過去完成」層
- 3混合型：過去的 if（had p.p.）＋ 現在的結果（would V + now）：If I had taken the medicine, I would feel better now.
- 4I wish 的兩層：wish + 過去式（與現在相反：I wish I were taller.）；wish + had p.p.（與過去相反：I wish I had gone.）
- 5「若非」三兄弟：Without/But for + N＝If it were not for（現在）／If it had not been for（過去）
- 6倒裝假設省略 if：If I were you → Were I you；If I had known → Had I known；If it should rain → Should it rain
- 7It's time + S + 過去式：It's time we went home.（該回家了——事實上還沒走）
大學學科能力測驗出題趨勢：學測必考：①判斷假設的時間層（現在相反 vs 過去相反）並選對動詞形式；②Had I known... 倒裝形式的還原；③without／but for 與 if 子句的互換；④I wish 後的時態選擇。翻譯題「如果當初……就會……」年年出現，是固定得分句型。
108 課綱對應
- 課綱學習內容 Ac-V-4：假設語氣的形式與語用功能。
- 課綱學習表現 3-V-3：能運用假設語氣表達與事實相反的情境。
- 課綱核心素養 B1：具備進階英語文表達能力。
進階探究・深度解析
假設語氣的本質是「時態的隱喻」：英文用「時間距離」比喻「現實距離」——過去式不表過去，而表「與現實隔了一層」。If I have time（真可能有）vs If I had time（暗示沒有）。理解這個隱喻就能貫通全部形式：想表達「更不可能／更遙遠的非事實」，時態就再退一層（過去→過去完成）。這也解釋了為什麼 were 不分人稱——它是「非現實標記」而非一般過去式。
解題先問「假設的是哪個時間」：看到 yesterday、last year、句中的 had p.p. → 與過去相反，選 would have p.p.；看到 now、today → 與現在相反，選 would + V。混合題（過去假設＋現在結果）的訊號是主要子句的 now：If you had saved the file, you wouldn't be in trouble now.——if 子句退到 had p.p.，主句因為有 now 只退一層 would be。學測選項常故意四種組合全列，時間定位是唯一解法。
倒裝假設是正式書面語的標配：Had the government acted earlier, the crisis could have been avoided.——省略 if、助動詞提前。只有三種可倒裝：Were（If I were → Were I）、Had（If I had known → Had I known）、Should（If it should rain → Should it rain）。學測閱讀的社論類文章常用此句型，看到句首 Had/Were/Should ＋主詞的結構，先還原成 if 子句再解讀，可避免誤判為疑問句。
章節試題（4 題・附詳解）
2.中等If Sarah _____ the weather forecast yesterday, she _____ her umbrella to work.
測驗重點：與過去事實相反
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正確答案：(B) had checked; would have taken
yesterday 表明是「與過去事實相反」：if 子句用 had p.p.（had checked）、主要子句用 would have p.p.（would have taken）。(D) 混合型需要主句有 now 等現在時間訊號，本句「帶傘上班」也發生在昨天，故兩邊都用過去層。
3.中等_____ I known that the tickets would sell out so quickly, I would have bought them earlier.
測驗重點：倒裝假設
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正確答案：(D) Had
空格後是「I known」——這是 If I had known 省略 if 後的倒裝：Had I known。倒裝假設只有三種：Were / Had / Should 提到句首。(A) If 之後應為 I had known 而非 I known。主句 would have bought 也印證是與過去相反的假設。
4.進階_____ the doctor's quick response, the patient would not be alive today.
測驗重點：but for 與混合時態
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正確答案：(A) But for
主要子句 would not be alive today 是假設語氣（與現在相反）——「若非」醫生當時的急救，病人現在就不會活著。表「若非」且搭配假設語氣的是 But for（= If it had not been for）。Because of / Thanks to 接「事實」不接假設；本句的 would 證明是非事實語氣。