doubt but that

我们已经知道,在肯定句中,doubt之后的宾语从句要使用连词whether或if:

1. He doubted whether they would be able to help. (EGS) 他拿不准他们是否能帮忙。

2. I doubt if he's honest. (LDCE) 我怀疑他是否诚实。

但是,在否定句中,doubt之后的宾语从句必须使用连词(but)that:

1. He never doubted that they would succeed. (EGS) 他从不怀疑他们会成功。

2. I don't doubt (but) that they'll accept at once. (CGEL) 我不怀疑他们会马上接受。

3. He didn't doubt but that( = that) snow would fall. (Walpole) 他不怀疑要下雪了。

doubt 用作名词时,情况亦是如此:

1. There is no doubt that if she had not lost her rudder she would have won the race easily. (New Concept English, Book 3, L. 25) 如果它没有失去船舵的话，它可能会轻而易举地赢得这次比赛的胜利的。

2. There's no doubt but that he's the guilty one. (LDCE)

他可能是有罪的。

3. I have no doubt but that he'll come.

我想他会来的。

从上面的例句可以看出, but that 是个复合连词, 可引出动词 doubt 的宾语从句或名词 doubt 的同位语从句。注意: but that 中的 but 常常省略。