▲没错，instance后接定语从句通常是用 where 来引导的。比如：

This is one instance where he is wrong. 这是他出错的一个例子。

The search finds every instance where the word appears. 搜索出了这个单词出现的每一处地方。

She cited an instance where their training had been a marvelous help in dealing with problems. 她举了一个所受训练为解决问题帮了大忙的实例。

Experts cite the country as an instance where human rights violations could lead to international intervention.  专家们以该国作为例子，说明侵犯人权可能会导致国际干预。

尤其是一些英语版的语法著作在描述语法现象时也经常用到 instances where。如：

A similar approach may be made to instances where the indirect object is omissible. 对于间接宾语可以省略的情况也可采取类似的处理办法。

We come next to instances where the verb cannot be intransitive, at least in the same sense. 下面我们谈一下动词不能用作不及物的例子，至少在表示同样意思时，不能用作不及物。

We have also noted some instances where either the adjective or the adverb forms appear, with little or no semantic difference. 我们还曾注意到，在有些例子中，不论是用形容词，还是用副词，在语义上几乎没有或完全没有区别。

We have also noted some instances where either the adjective or the adverb forms appear, with little or no semantic difference. 我们还曾注意到，在有些例子中，不论是用形容词，还是用副词，在语义上几乎没有或完全没有区别。

In instances where the passive is inapplicable because the object is a clause, we can test for the presence of an object by adding a coordinate clause with a pro-form and making the second clause passive. 在那些由于宾语是个分句而不适宜用被动语态的句子中，我们可以通过加上带代用式的并列分句将第二个分句变为被动语态的办法来检验句子是否有宾语。

▲但是，instance后面就不能接 when 引导的定语从句吗？也不是！

比如《朗文当代英语词典》就在 instance 词条用黑体字给出了 instance where / when 这样的语法结构，但遗憾的是，该词典给出的例句只有 instances where：

instances where safety regulations have been breached 违反安全规章的例子

▲我在BNC上查了一下，查到了以下一些例子：

1. …your readers may be interested in a recent instance when Mrs Thatcher was equated with the Queen. 

2. Praise every instance when your child is learning something new (e.g. remember to say ‘thank you’). 

3. Manuel Golias recalls an instance when a village was attacked. 

4. An extreme example would be an instance when there are signs of child abuse and the cues are not picked up by people outside the home setting. 

5. Cases of suicide are well-documented, and there was at least one instance when several people barricaded themselves into a flat and refused to leave. 

6. As we shall see more clearly after studying Chaucer's other fabliaux and uses of fabliau, the Shipman's Tale stands out as the particular instance when Chaucer uses a fabliau to place fabliau in a critical light, examining fabliau as an extant genre rather than exploiting it for some other purpose. 

7. There was one instance when the tanker had left and we were low on fuel that we radioed in to say we were coming home. 

▲另外，我在新概念英语第三册的 Lesson 35 Justice was done 发现有一个 instances when 的用例：

There are rare instances when justice almost ceases to be an abstract conception. 在极少数时候，正义不再是一个抽象的概念。

▲还有在张道真的《现代英语用法词典》的 instance 词条也有一个  instance when 的例子：
I can’t think of a single instance when Mother was unfair. 我想不出一个事例能说明母亲是不公正的。

■用 instance where 和 instance when 的基本区别是：若将 instance 视为“地点”看待，则通常用 instance where；若将 instance 视为“时间”看待，则通常用 instance when。