but for，要不是，其本身就含有對(duì)于已發(fā)生的事情的一種假設(shè)，所表示的是過去的某一個(gè)狀態(tài)，例如說I'd have been lost but for you.要不是你，我就走迷路了。

but for要不是，本身就含有對(duì)于已發(fā)生的事情的一種假設(shè)，所以表示的是過去的某一個(gè)狀態(tài)舉個(gè)例子：But for his help,i couldn't have made such big progress.要不是他的幫助，我不會(huì)取得如此大的進(jìn)步！

給你一個(gè)公式（基本上是這樣）：虛擬語氣里，表示對(duì)現(xiàn)在虛擬的時(shí)候，主句謂語動(dòng)詞do變did，從句變would do；表示對(duì)過去已發(fā)生的虛擬是，主句變have done從句變would have done（注，有時(shí)would可用could、might、should等詞語代替。

But for you, they might have given us the slip.

要不是你，我們可能已經(jīng)被他們甩掉了。

I'm changing my email address but for the meantime you can use the old one.

我要更換電郵地址，不過那個(gè)舊的暫時(shí)也還可以用。

I was sure she knew the answer but for some reason she hung back.

我敢保證她知道答案，但不知為什么她不敢說出來。

There's still another ten minutes of the game to go, but for practical purposes it's already over.

比賽雖然還有十分鐘，但實(shí)際上等于已經(jīng)結(jié)束了。