Q：But that there is water, there would be no fish. 這句是假設語氣的條件句，請問 But that 子句為何可以用現在式動詞?

A：But that 的意思是「若非；要不是」，是條件句的另一種句型。它的後面接子句，不過我們也可將之改為「but for + 名詞」(而 but for 又等於 without)。

由於 But that 子句敘述的是事實，所以若為現在式，則使用簡單現在式，若為過去式，則使用簡單過去式。而主要子句係屬假設的敘述 (非事實)，所以若與現在事實相反，則句型為「主詞 + would/should/could/might + 原形動詞」；若與過去事實相反，則句型為「主詞 + would/should/could/might + have + P.P.」。不過，它們也都可以改為用 if 引導的假設語氣條件句。注意：此時 if 子句的敘述必須分別與現在和過去事實相反。請看下面的例句 (第一句為問題中的句子) 並加以分析，以徹底瞭解這些實用句型及其變化：

1. But that there is water, (現在事實的敘述) there would be no fish. (與現在事實相反) — (要不是有水，就不可能有魚)
   = If there were no water, (若無水 — 與現在事實相反) there would be no fish.
   = But for water, there would be no fish.
   = Without water, there would be no fish. (but for = without，意思亦是「若非；要不是」，但後面接名詞)
2. But that you helped me, (過去事實的敘述) I would not have succeeded. (與過去事實相反) — (要不是你幫忙，我就不會成功)
   = If you had not helped me, (如果沒有你的幫忙 — 與過去事實相反) I would not have succeeded.
   = But for your help, I would not have succeeded.
   = Without your help, I would not have succeeded.