but for和but that 具体的语法讲解，中英举例说明（看清问题，回答好的加分）

Question

都表示“要不是”吧？怎么区分呢？貌似还是虚拟语句？
not that John doesn't want to help you ,（but that ）it's beyound his power.非限定性定语从句，用逗号隔开，不用“that”,这句我就不懂了

Answer 1

but for 如果没有，要不是，若非
But for my brother’s help ， I would not have finished the work .

but that 如果没有,要不是，若非；连接宾语从句，相当于that ，不译出词义
He would have said no but that he was afraid .
There's no doubt but that he's the guilty one .
Who knows but that he may succeed ?

从用法上讲，两者最大的区别在于前者后面接名词或相当于名词的词,如动名词；后者后面要接从句。

Answer 2

你好。非常简单。都解释为“要不是- -- -- ”
1 but for + 短语
--------- But for your help, I would have gone bankrupt ---------- 通常用于虚拟语气结构。
2 but that + 句子
--------- He would have died but that they sent him to hospital in time. ---------也是用于虚拟语气结构。追问

but for 能开头使用，but that 就不能？

追答

but that一般不放在句首，也不需要如此。

本回答被提问者采纳

Answer 3

but that 若非，后加句子
She would have fallen but that I caught her. 如果不是我抓住她，她就会跌倒了。
来自《现代英汉综合大词典》
but for 倘没有，要不是，后加短语
But for the rain we should have had a pleasant journey. 要不是下雨，我们会有一次愉快的旅行。
来自《简明英汉词典》
He has many faults, but for all that I like him. 他有许多缺点，尽管如此，我仍喜欢他。
来自《简明英汉词典》