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(guò)去的某一個(gè)狀態(tài)。例句：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！

but for相關(guān)例句

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(guò)那個(gè)舊的暫時(shí)也還可以用。

I'm not afraid for me, but for the baby.

我擔(dān)心的不是自己，而是嬰兒。

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(shuō)出來(lái)。

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。

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。

虛擬語(yǔ)氣

虛擬語(yǔ)氣表示說(shuō)話人的主觀愿望、猜疑、建議或與事實(shí)不符的假設(shè)等，而不表示客觀存在的事實(shí)。虛擬語(yǔ)氣是由句中的謂語(yǔ)動(dòng)詞的特殊形式表示出來(lái)的。如：

If I were a bird，I would be able to fly in the air.

如果我是一只小鳥(niǎo)，我就能在空中飛行。

I wish I could pass the examination.

我希望我能通過(guò)考試。

Hope you succeed!

祝你成功！

If only we had been college students last year!

上一年我們要是大學(xué)生該多好！