有读者问： 有这样一个句子：
(1)But he wasn't sick — which would be a good excuse.
请问 which 在此指代什么？
关系代词在这里不是指代其前的否定句，而是指代其前的肯定结构。由于 which 从句用的是虚拟时形式 would be, 所以其前的肯定结构应是一个含蓄的条件从句 if he were sick。 这种“否定陈述句+指代肯定结构的定语从句”结构在英语里常可见到，再如：
(2)They are no better （as they sometimes claim ）and no worse （as their enemies often state ）than anyone else. （as they sometimes claim 实指 they are better, as their enemies often state 实指 they are worse）
有时否定陈述句之后是一个名词性短语，如：
(3)One of the peculiarities of the Eastern bazaar is that shop-keepers dealing in the same kind of goods do not scatter themselves over the bazaar — a reasonable arrangement to avoid competition — but collect in the same area so that, I am told, they can form a closely-knit guild against injustice or persecution.
（这里的名词性短语a reasonable arrangement to avoid competition 所指的显然不是 shopkeepers ... do not scatter themselves..., 而是 if they scatter themselves...）
