假設語氣在中文之中只要在句子的開頭說"如果"或"假設"就可以了，例如: "如果明天下雨的的話我將會待在家裡"，"如果我是一隻貓咪的話，我就可以一天睡16小時"，”如果我昨天有時間的話，我就會打掃房間"，"如果我年輕時認真讀書的話，我現在就不用補習" ；但是在英文中，這些假設語氣的句子就要考慮到說話者想表達的情境到底是有可能發生的事情，還是不可能發生的事情，以及時間點的問題，來使用不同的動詞時態及情態助動詞，這導致多數學習者對假設語氣用法的印象就像背了一堆公式但還是霧煞煞，在考試時還是常常選錯答案或者在日常生活中用錯假設語氣的句型，我建議大家在學假設語氣之前應該要先對英文12時態有基本的認識，再來學習假設語氣用法，這是因為假設語氣的句構其實是建立在時態的基礎上，如果你不懂什麼是現在簡單式、未來簡單式、過去簡單式，過去完成式，那直接就學習假設語氣是非常難以理解又痛苦的，如果你已經對英文時態有基本的認識，那麼我會建議在學習假設語氣時儘量用例子情境去理解，公式畢竟只是輔助你，接著試著把假設語氣的基本概念套用到你自己的生活情境中去造句，才能真正掌握假設語氣正確的用法，本文將對假設語氣常用的基本型態及混合式，多益考試常考的相關概念(例如：假設語氣倒裝、Wish的用法與假設語氣相似的其他用字)來做說明，並附上相關的假設語氣題目讓大家練習，希望能幫助讀者攻克假設語氣。
If I don’t drink a cup of latte in the morning, I feel sleepy during the day.
= I feel sleepy during the day if I don’t drink a cup of latte in the morning.
If I have enough time, I play with my cats every evening.
= I play with my cats every evening if I have enough time.
If I don’t eat dinner, I always get hungry at midnight.
=I always get hungry at midnight if I don’t eat dinner.
If you leave ice cubes in the sun, they melt.
= Ice cubes melt if you leave them in the sun.
If water reaches 100 degrees, it boils.
= Water boils if it reaches 100 degrees.
When you leave ice cubes in the sun, they melt.
= If you leave ice cubes in the sun, they melt.
When water reaches 100 degrees, it boils.
= If water reaches 100 degrees, it boils.
If my cell phone rings, just ignore it.
If anyone calls, please transfer the call.
第一式假設語氣用以描述「未來有可能發生」的事情，if子句用現在簡單式，主要子句用未來簡單式will/be going to + 原型動詞或其他情態助動詞can/could/may/might/should + 原型動詞等等來表達，我們來看幾個例句:
If I don’t drink a cup of latte tomorrow morning, I will feel sleepy during the day.
If I have enough time, I will play with my cats tonight.
If it rains tomorrow, I am not going to the library.
If Susan doesn’t leave soon, she will miss her flight.
A: What do you usually do in the evening?
If I have enough time, I play with my cats every evening.
-> A問我晚上通常在做什麼? 我說如果我有時間，我每天傍晚都會跟貓咪們玩耍，這是一個常態性的動作，過去現在未來皆是如此。
A:What are you going to do tonight?
B: If I have enough time, I will play with my cats tonight.
-> A問我今天晚上要做什麼? 這是個特定未來的情境，我說如果我今天晚上有時間，我今晚將跟我的貓咪們玩耍。
If you want to lose weight, you should do exercise every day. 如果你想要減重的話，你應該要每天運動。
If I win the lottery, I can buy a mansion or travel around the world.如果我中樂透，我就可以買一棟豪宅或環遊世界。
If it rains tomorrow, I might stay home.
If anyone should call, I will be at my grandfather’s home.
If anyone calls, I will be at my grandfather’s home.
那這兩句話跟有什麼差別呢?兩句話翻成中文是幾乎一樣的， 在if 子句中使用should代表這件事發生的機率更不確定，If anyone should call, I will be at my grandfather’s home. 如我有人打給我的話，我將在我外公家，但我不認為有人會打給我，有人打電話給我的機率是很低的。我們再來看兩個例句:
If it should snow tomorrow, I will stay home. 如我明天下雪的話我將待在家，但我覺得明天下雪的機率應該很小。
If Winnie should come this evening, give her this letter. 如果Winne今晚會來的話就拿給她這封信，但事實上我覺得她應該不會來，她來的機率很小。
True: I am not a cat. I can’t sleep up to 16 hours a day.
真實情境: 我不是一隻貓咪，我也不能一天睡16小時。 Conditional: If I were a cat, I could sleep up to 16 hours a day. 假設情境: 如果我是一隻貓咪的話，我就可以一天睡16小時。
-> 這邊大家應該有注意到be動詞是用were來表達，而不是was，在正式的文體中，不管前面的人稱是什麼都是用were來表達，當然在非正式的口語中，也會聽到有人用was，例如: If I was cat, I could sleep up to 16 hours a day. 也是可以的，但是有些人認為用were文法才是比較正確的。
True: He is not a bird, so he can’t fly.
Conditional: If he were a bird, he could fly.
True: It is raining right now, so I will not go to the coffee shop.
Conditional: If it were not raining right now, I would go to the coffee shop.
True: I don’t have a lot of money, so I won’t buy a house.
Conditional: If I had a lot of money, I would buy a house.
True: Susan doesn’t take her teacher’s advice, so she may not learn more quickly.
Conditional: If Susan took her teacher’s advice, she might learn more quickly.
If I am not too tired, I read a poem before I go to bed.
If I am not too tired, I will read a few pages of my favorite novel.
If I were not so tired, I would clean my room.
My coworker and I are talking about our daily routine.
A: What do you usually do before you go to bed?
B: If I am not too tired, I usually read a poem before I go to bed.
I was busy at work today. After work, my friend asked me, “Hey Rose, what are you going to do tonight? Any plans?”
I said, “No, if I am not too tired, I will read a few pages of my favorite novel tonight.”
I was busy at work today and I am exhausted. My room is messy, but I don’t think I have the energy to clean my room. If I were not so tired, I would clean my room tonight.->我今天白天上班時工作繁忙，然後我現在很累，我也沒力氣打掃房間，如果我不是這麼累的話，我今晚會打掃一下我的房間，這是與現在或未來事實相反的假設和想像。
第三式假設語氣，用以描述「與過去的事實相反」的情境，大家要注意的是原本真實發生的時間點都在過去，要描述與過去事實相反的假設: if子句用過去完成式had +P.P. ，主要子句用would have + P.P.或其他情態助動詞could/might/should + have +P.P. 來表達，我們來看幾個例句:
True: I didn’t study hard in the past, so I didn’t pass the final exam.
Conditional: If I had studied harder, I would have passed the final exam.
True: I wanted to send the package yesterday, but I didn’t have enough time.
Conditional: If I had had enough time, I would have sent the package yesterday.
True: It was raining yesterday morning, so I didn’t go hiking.
Conditional: If it had not been raining yesterday morning, I might have gone hiking.
True: You didn’t leave earlier last night, so you didn’t catch the flight.
Conditional: If you had left earlier last night, you could have caught the flight.
0 .If I have enough money, I donate 500 dollars to the Stray Cats Association every month.
1 .If I have enough money, I will donate 500 dollars to the Stray Cats Association next month.
2. If I had enough money, I would donate 500 dollars to the Stray Cats Association.
3. If I had had enough money last month, I would have donated 500 dollars to the Stray Cats Association.
If I have enough money, I donate 500 dollars to the Stray Cats Association every month.
(=When I have money, I donate 500 dollars to the Stray Cats Association every month .)
If I have enough money, I will donate 500 dollars to the Stray Cats Association next month.
If I had enough money now, I would donate 500 dollars to the Stray Cats Association.
If I had had enough money last month, I would have donated 500 dollars to the Stray Cats Association.
1. Situation: I usually drink a cup of black tea in the afternoon to refresh myself. That is a true fact. In other words: If I (not, drink)__________ a cup of black tea in the afternoon, I (feel) _________tired.
2. Situation: I am not rich, so I won’t buy a house or travel around the world. In other words: If I (be) _____________ rich, I ______(buy) a house or travel around the world.
3. Situation: I was busy and didn’t have time to clean my room last night. In other words: If I (have) _________enough time, I (clean) ___________my room last night.
4. Situation: According to the weather forecast, the weather is going to be sunny tomorrow. In other words: If the weather is nice tomorrow, my family (go) _______hiking.
5. Situation: It’s rainy and chilly today. I want to go running, but I can’t. In other words: If the weather (be) ______nice today, I (go) ________ running.
6. Situation: It was hot and humid yesterday. The temperature soared to over 40°C (104°F) yesterday. In other words: If the weather (be, not) ________ so hot, we (go) _________to the beach yesterday.
7. Situation: The report says that this candidate embezzled thousands of dollars from the bank. If the report (be) ____true, we will not offer him the position.
8. Situation: I don’t have an oven in my kitchen, so I can’t make a chicken casserole. In other words: If I (have) _____an oven in the kitchen, I (can) ______make a chicken casserole for dinner.
9. Situation: I didn’t know that the baby was sleeping when I came in. I made some noise and the baby woke up. If I (know) ________the baby was sleeping, I (come)______ in quietly.
10. Situation: There was an online workshop yesterday morning. I didn’t know that, so I didn’t take the class. In other words: If I (know) _______that there was an online workshop yesterday morning, I (have) _______the class.
2. were, would buy
3. had had, would have cleaned
4. will go
5. were, would go
6. hadn’t been, would have gone
8. had, could make
9. had known, would have come
10. had known, would have taken
1. If you don’t eat breakfast, what always happens?
EX: If I don’t eat breakfast, I always get hungry and feel dizzy at work.
2. What will you do if you go to Japan?
EX: If I go to Japan, I’ll try their noodles.
3.If you want to learn a language faster, what should you do?
EX: I should use the language every day.
4.If you had only 24 hours to live, what would you do?
EX: If I had only 24 hours to live, I would spend time with my dear family and friends.
5.If you could be an animal, what animal would you be?
EX: If I could be an animal, I would be a cat or a panther because cats/panthers are elegant animals.
6.How would your life have been different if you had been born a girl/ boy?
EX: If I had been born a boy, my parents wouldn’t have worried about my safety so much. I could have lived overseas or travelled alone.
假設語氣的混合式是由假設語氣第二式與第三式所組成的情境，這邊大家要先搞懂原本真實情境的句子事件所發生的時間點是落在過去還是在現在，假設語氣混合式可分為兩類: "過去的因導致現在的果" 以及"現在的因導致過去的果"
True: I didn’t study Japanese in school, so I watch Japanese animated films with Chinese subtitles.
Conditional: If I had studied Japanese in school, I would be able to watch Japanese animated films without Chinese subtitles.
假設情境：如果我過去在學校有學習日文，我現在就可以不需要中文字幕而看懂日本動畫。在if 子句中，這是與過去事實相反的假設，所以用假設語氣第三式had +P.P.; 結果句是與與現在事實相反的假設，所以用假設語氣第二式would+原型動詞。
True: Sue didn’t wear a mask while going out and didn’t sanitize her hands after she got home. Now she is sick. 真實情境：Sue出門時沒有戴口罩，回家後也沒消毒手，所以她現在生病了。
Conditional: Sue wouldn’t be sick now if she had worn a mask while going out and had sanitized her hands after getting home.
假設情境：如果那時候Sue 出門時有戴口罩，回家後也有消毒手，她現在就不會生病。結果句是與現在事實相反的假設，所以用假設語氣第二式would+原型動詞，if 子句中是與過去事實相反的假設，所以用假設語氣第三式had +P.P.
Situation: My friend, Jan, invited me to her wedding reception. However, I don’t live in the United States. I couldn’t go to Jan’s wedding party.
Conditional: If I lived in the United States, I would have gone to Jan’s wedding party.
假設情境：如我我一直住在美國的話(這是與現在事實相反的情況，用假設語氣第二式，if子句用過去簡單式的動詞)，我那時候就會去參加Jan的婚宴 (這是與過去事實相反的假設情況，用假設語氣第三式表達結果句would have +P.P.)
Situation: Kate is not good at time management, so she didn’t finish the project on time.
If Kate were good at time management, she would have finished the project on time.
假設情境：如果Kate擅長時間管理的話(這是與現在事實相反的情況，用假設語氣第二式，if子句用過去簡單式的動詞，那因為是Be動詞所以我們不管人稱是什麼都會寫were)，她當時就會準時完成專案報告(這是與過去事實相反的假設情況，用假設語氣第三式來表達結果句的部分would have +P.P.)
1.If I had majored in literature in school, I _____ a writer now. A) could have been B) had been C) could be D) will be
2. If she had studied English harder in school, she _________ so many English classes after work now. A) wouldn’t have to take B) won’t have to take C) would have had to take D) cannot take
3. If my mom___ tidy, she wouldn’t have misplaced her keys and glasses half an hour ago. A) is B) were C) doesn’t be D) didn’t be
4. If you hadn’t gone over the speed limit five minutes ago, you _________ a speeding ticket now. A) wouldn’t have got B) wouldn’t get C) won’t get D) hadn’t got
5. If I were rich, I __________ more money to the charity last week. A) would have donated B) would donate C) will donate
7. True: I didn’t go to bed earlier last night, so I feel sleepy and have a headache now.
8. True: I didn’t buy enough canned cat food, so I am worried about running out of it now.
6. If I knew Japanese, I would have gone backpacking in Japan last year.
7. If I had gone to bed earlier last night, I wouldn’t feel sleepy and have a headache now.
8. If I had bought more canned cat food, I wouldn’t be worried about running out of it now.
If I were you, I would tell him the truth.
-> Were I you, I would tell him the truth.
If you had asked me to pick you up, I would have helped you.
-> Had you asked me to pick you up, I would have helped you.
If anyone should call, please let them know I won’t be available until 4 o’clock.
-> Should anyone call, please let them know I won’t be available until 4 o’clock.
1. If it should snow tomorrow, I will stay home.
2. If I were a cat, I could get enough sleep every day.
3. If they had foreseen the outcome, they wouldn’t have done that.
4. If you should change your mind, give us a call right away.
5. If I were rich, I would hire an interior designer to renovate my old house and change it into a cat house.
2. Were I a cat, I could get enough sleep every day.
3. Had they foreseen the outcome, they wouldn’t have done that.
4. Should you change your mind, give us a call right away.
5. Were I rich, I would hire an interior designer to renovate my old house and change it into a cat house.
I wish you a Merry Christmas.
I wish you all the best in your future endeavors.
除此之外， “wish to + 原型動詞” 有want to 的意思，例如:
I wish to see the chef.
I wish to make an appointment with our biggest patron.
但當wish的意思是"希望"時，跟hope這個字有什麼差異了? 倒底何時要用wish何時要用hope呢? 簡單地來說:
你會說: I hope you can get the score you want.
這邊不能用I wish 來講，因為這是真實情境中有可能發生的事情
你會說: I hope you get well soon.
這邊一樣不能用I wish 來講，因為這是真實情境中有可能發生的事情
wish 用以表示不太可能實現的願望(unreal, impossible, unlikely)，是描述真實情況相反的(counterfactual)、假設的(hypothetical)情境，通常語氣上帶有挫折失望、懊悔、厭煩的感覺(frustration, regret, annoyance)，wish 後面接上that子句的用法也與上述if子句假設語氣類似，子句的that常被省略，wish假設語氣的句子大致可分為兩類:
I don’t think you “will”-> I wish you “would”
I don’t think you “are going to”-> I wish you "were going to”
I don’t think you “can”-> I wish you "could”
My friend is always complaining about her job. This has been going on for a while. I suggested that she quit her job in the past, but she didn’t take my advice. She still has her job now. Therefore, I say, “I wish you would get a new job.” -> I am frustrated that she hasn’t quit her job. I think she should quit, but probably I think she won’t.
I don’t think you will get a new job. -> I wish you would get a new job.
情境二: My family is going to have a reunion next weekend. I asked my brother to come home, but he said, “I am busy with my work. I have no time. I am not going to be home next weekend.” I feel a bit disappointed because I haven’t seen him for a long time and I miss him very much. I wish my brother could come home next weekend. -> I hope that my brother will change his mind, but I don’t necessarily expect this will happen.
I don’t think you can come home. -> I wish you could come home.
(It’s a pity. It’s too bad. This is the way it is, but I wish it were not that way. )
I wish I didn’t have to work tonight. Because if I didn’t have to work tonight, I could play with my cats. However, the real situation is that I have to work tonight and it is impossible for me to play with my cats. It’s too bad, but this is how it is.
I have to work tonight. -> I wish I didn’t have to work tonight.
情境二: I wish I were rich. Because if I were rich, I could buy a big house and my cats could have more space to run around. But the real situation is that I am not rich and it is unlikely to buy a big house. It’s a pity, but this is how it is. I don’t have a big house, so my cats can’t have more space to run around.
I am not rich. -> I wish I were rich.
(It was a pity. It was too bad. This was the way it was, but I wish it hadn’t been that way. )
I didn’t buy one more carton of milk two days ago and now I am running out of it. However, I am too busy to go shopping today. I wish I had bought one more carton of milk.
I didn’t buy one more carton of milk two days ago. -> I wish I had bought it.
情境二:I am so tired now and can’t concentrate on my work because I didn’t go to bed at a reasonable hour last night. Now I regret staying up late last night. I wish I had gone to bed before midnight last night.
I didn’t go to bed before midnight last night. -> I wish I had gone to bed before midnight last night.
1.My house is not big. I wish my house ________ (be) big.
2. It’s raining outside, so I can’t go cycling. I wish it ________(not rain) right now.
3. My friend just sent me a message asking me if I would like to go to a trade show with her. I really want to go to that trade show tomorrow, but I can’t take tomorrow off. I wish I __________(can) take tomorrow off.
4. The COVID-19 pandemic probably won’t be over soon. I wish the pandemic __________ (be over) soon and our life could get back to normal.
5. Jessica can barely make ends meet. She wishes she _______(can) earn more money to support her family.
6. I usually do yoga half an hour every day so that I can sleep better. However, I didn’t sleep well last night because I didn’t have time to do yoga. I wish I _________(can do it).
7. My friends went hiking on the mountain and had a good time. They look so happy and I regret not going with them. I wish I ________(go) with them.
8. Julia has been sitting there brooding for a long time. I wish she _________(tell) me what’s wrong.
9. I wasn't wearing a helmet when I fell off my bike. I hit my head on the ground and had a minor concussion. I wish I _________(wear) a helmet.
2. weren’t raining
4. would be over
6. could have done it
7. had gone
8. would tell
9. had been wearing
假設語氣的用字除了 if和wish之外，多益考試中常見的還有 providing (that), provided (that), as/so long as, on (the) condition that, 例句如下:
You can borrow these books providing (that) you return them before Friday. 你可以借閱這些書只要你在周五前歸還。
You are welcome to join us for lunch provided (that) you pay for your own meal. 歡迎你加入我們一起吃午餐，只要你付你自己的餐錢。
You can get off work early today so/as long as you are done with the project. 你今天可以提早下班只要你已經完成專案了。
I'll help you with your homework on (the) condition that you teach me how to use this software program. 你的功課我會協助你，條件是你要教我怎麼使用這個軟體。
0.假設語氣第零式: If I have enough time, I play with my cats every evening. if子句用現在簡單式，結果句(或稱為主要子句)也是用現在簡單式。
1.假設語氣第一式: If I have enough time, I will play with my cats tonight. if子句用現在簡單式，主要子句用未來簡單式。
2.假設語氣第二式: If I had a lot of money, I would buy a house. if子句用過去簡單式，主要子句用would+ 原型動詞來表達
3.假設語氣第三式: If I had studied harder, I would have passed the final exam. if子句用過去完成式had +P.P. ，主要子句用would have+P.P. 來表達
If I were a bird, I could fly. 有的同學會問說難道不能寫If I was a bird, I could fly. 嗎? 在正式的文體中若要表達這樣的假設語氣，不管前面的人稱是什麼都是用were來表達，當然在非正式的口語中，也會聽到有人用was 也是可以的，但是有些人認為用were文法才是比較正確的。
hope 用以表示可實現的願望; wish 用以表示不太可能實現的願望 例如: I hope she likes the gift. 我希望她喜歡這份禮物。這是有可能實現的願望；I wish I were a bird. 我希望我是一隻鳥。這是不可能實現的願望。
假設語氣的句子省略掉if，主詞與動詞的位置對調，例如: If I were you, I would tell him the truth.-> Were I you, I would tell him the truth. If anyone should call, please let them know I won’t be available until 4 o’clock.-> Should anyone call, please let them know I won’t be available until 4 o’clock.
假設語氣的考題多半出現在多益第五部分的單選題，比較常考的是假設語氣基本句型及省略if需要倒裝的概念，假設語氣混合式的考題出現機率較低。例如: Mr. Mark _____ to manager had he succeeded in getting that business deal. A) is being promoted B) will be promoted C) has been promoted D) would have been promoted 正確答案為: D 題意是當初若Mr. Mark有簽下那筆商業交易的話，他早就被提拔為經理一職了。這邊考的是假設語氣第三式與省略if句子倒裝的概念，原句為: Mr. Mark would have been promoted to manager if he had succeeded in getting that business deal.
Azar, Betty Schrampfer.Understanding and Using English Grammar. 3rd ed. New York: Pearson Education, 1999.
Swan, Michael. Practical English Usage.3rd ed. Oxford: Oxford UP, 2005.
柯旗化。New English Grammar新英文法。高雄市: 第一出版社。