第3. 類條件句的前段裡含有 had + 過去分詞，來構成一個過去完成式的句型，後段含有would, could或 might + have + 過去分詞，例如，“If I had known, I would have gone somewhere else.” (早知道的話，我會選擇到別的地方去。) 這個句型裡，過去分詞扮演著關鍵性的角色，後面我們再回到這個議題。我們來看幾個稍微簡化的真實例子。
If I had done that, I would have lost my beloved vocation. 稍微正式一點的話，也可以說成： Had I donethat, I would have lostmy beloved vocation. 我當時這麼做的話，我就會失去我心愛的職業。
If you had investedin this a few years ago, you would have earned162% on your money. 如果你在幾年前已經做了這樣的投資，你現在的回報率會是162%。
If I had asked it this way, how do you think he would have answeredthat question? 如果我當時用這種方式來問那個問題的話，你認為他會怎樣回答？
I’m convinced she would have been the best vice-president of the bank, if she had gotten the chance. 我深信，只要她當時有機會的話，她一定會是銀行有史以來最好的副總裁。
If you would have askedthem, they would have said something very different. 如果你當時問過他們的話，他們的說法會很不一樣。
原先的 “if you had asked” 已經變成了 “if you would have asked”，前段用得時態跟後段變得一樣了，都不用 “had asked” 而用 “would have asked”！這不是偶發的以兩個例子，我們再來看幾個簡化的實例：
If it would have been me, I would havejust made those statements. 當時如果換是我的話，我就會說出那幾句話。 傳統的「正確」文法：If it had been me, Iwould have just made those statements.
Actually, if it would've been me, I would've used a very clever trick I know. 實際上，換是我的話，我會耍個我知道的絕妙花招。
傳統文法：Actually, if it had been me, I would've used a very clever trick I know.
I wish that I would have known about that a little sooner, so that I could have got her the ID card much sooner. 真希望我能早點知道那件事，那樣的話我可以早點幫他辦好證件。
傳統文法：I wish that I had known about that a little sooner, so that I could have gotten her the ID card much sooner.
If you would have told me that my boss would become the US president, I probably would have told you you’re crazy. 如果你當時跟我說，我的老闆將來會成為美國總統，我大概會跟你說你瘋了。
傳統文法：If you had told me that my boss would become the US president, I probably would have told you you’re crazy.
It would have been funny if I wouldn’t have been so painfully shy. 我當時如果沒那麼害羞的話，事情就會很好笑。
傳統文法：It would have been funny if I hadn’t been so painfully shy. 或：It would have been funny had I not been so painfully shy.
I would definitely not have been so calm if it would have been a poisonous snake. 當時如果遇到的是毒蛇的話，我絕對不會那麼從容沒事的樣子。
傳統文法：I would definitely not have been so calm if it had been a poisonous snake. 或： I would definitely not have been so calm had it been a poisonous snake.
第3. 類條件句的前段用的是過去完成式，也就是 had + 過去分詞，例如 “had told”，可是過去完成式這個時態本身最近在英語裡用得比以前越來越少，有些場合還是一定得用，可是現在常被簡單過去式取代，用了過去完成式聽起來比較正式，沒那麼口語化。下面是過去完成式被簡單過去式取代的實例：
If you told me five years ago that today I'd be delivering a talk about our individual power to make a difference, I would have cringed. (原應該是： “If you had told me…”) 五年前你如果跟我說，我今天會發表有關如何憑著自己的力量來做出貢獻，我會表現出很不以為然的樣子。
第3. 類條件句和過去完成式兩種句型，都要用到過去分詞 (past participle)，而如本文開頭所提，像 go went gone 一類的不規則動詞已慢慢變成了 go went went，所以這兩個文法上的大改變跟過去分詞本身的變化有連帶關係。結論是，凡是跟過去分詞有關的文法句型，都可能會被牽連到，容易產生一些新變化。
第3. 類條件句，後段子句裡的 would，在很多人的心目中，跟「假設語氣」的關係最深，反之，含有 had 的過去完成式，跟假設語氣的關聯相對弱，所以在假定某事時，「假設語氣」味道較濃厚的 would，不知不覺也跑道句子的前段裡去，來取代 had 子句。