※ 引述《harry1234585 (UglyLoser)》之銘言：
: 課本上的句子：
: Many people might have died if there was a disaster.
: 疑問：
: 與過去事實相反的假設,if 子句不是要用過去完成式嗎：Many people might have died
: if there had been a disaster.
: 求教是我理解有問題還是課本有謬誤
這個句型，在板上好像討論蠻多次了。之前經濟學人那篇，也有用過去完成式，假定某件
事成真。
如果要用過去完成式，那時態就要設定在過去式。這可以畫時間軸就知道了，假定A那件事
情發生成真，那B這件事就會怎樣。如果一個用現在完成式(might have)，一個用過去完成
式就說不過去了(had been)。
要改寫成過去完成式的話，就要這樣子寫：
Many people would die if there had been a disaster. （經濟學人那句也是
had .... + would，兩者都是在過去時間軸假設。）
經濟學人原句，提供參考
"After Britain had left the eu early next year, the hard work of negotiating a
trade agreement would begin."
另外我特別查了Oxford Modern English Grammar，相關用法。
但實際上查到資料，發現使用更彈性，並沒有一定要過去完成式這種說法，甚至不想要用
if 都沒關係。
9.2.2.3 The modal past tense. (Page. 250)
The past tense of verbs can be used to talk about modal situations, for example
situations that are hypothetical or non-factual. For this reason we call it the
modal past tense, that is, conditions which are most likely to be fulfilled.
They can be introduced by if(only), imagine if, or suppose/supposing.
例句:
If you turned up for a day's shooting, the pheasants would die laughing.
If I was to go to Dubai, I can get things like electrical goods.
If only he had a darling, cuddly, relaxing dog, perhaps he wouldn't be such a
miserable toad.
不用if
Supposing he had the management team who so intelligently advise Beckham; might
it have made difference ?
也可以用It's time or wish
例句:
It's time people knew how their money was being spent. (事實上人們還不知道)
I wish it was over now. (但與現實相反)
這句也可以寫成
I wish it were over now. 但were表示subjunctive verb form (西班牙文有，但是英文
沒有，不過Be動詞是例外)，用來表示a particular type of modal situation，來表示強
烈希望這件事情發生。
P.278
例如:
If I were you, I'd happy for the York position just for the experience.
你甚至可以用現在式，表示真的有可能完成
We can turn the if-clause in an example like into a clause expressing an open
condition, that is, a condition that can realistically be fulfilled, by
changing the past tense forms to present tense forms in both clauses.
例句:
If you turn up for a day's shooting, the pheasants will die laughing.
如果你學的只有過去完成式的用法，我建議可以換一本了。
不妨參考一下這本
Oxford Modern English Grammar
可以在Amazon 或 Kobo買到，現在Amazon kindle version 還有特價。