很多人搞不清replace和substitute for用法的区别。replace比较易用，但用substitute for 的时候很容易搞错。如下予以分析。

Substitute vt, vi

If you substitute one thing for another, or if one thing substitutes for another, it takes the place or performs the function of the other thing. 以…代替; 代替

They were substituting violence for dialogue.

他们在以暴力代替对话。

He was substituting for the injured William Wales.

他那时在代替受伤的威廉·威尔士。

replace  

1.       If one thing or person replaces another, the first is used or acts instead of the second. 代替; 取代

例：One species of tree replaces another as a forest ages.

随着森林老化，一种树会取代另一种树。

例：...the lawyer who replaced Robert as chairman of the company.

…取代罗伯特成为公司主席的那位律师。

2.       If you replace one thing or person with another, you put something or someone else in their place to do their job. 用…代替; 用…替换

例：I clean out all the grease and replace it with oil so it works better in very low temperatures.

我清除掉了所有的油脂，以油替换，因此它在很低的温度下运转得更好。

3.       If you replace something that is broken, damaged, or lost, you get a new one to use instead. 换下 (坏的); 换上 (新的)

例：The shower that we put in a few years back has broken and we cannot afford to replace it.

我们几年前安装的淋浴器坏了，但没钱换新的。

4.       If you replace something, you put it back where it was before. 把…放回原处

那么substitute for和replace有什么区别呢？看下面两种情况:
一种是人做主语，substitute A for B,或replace A with B,这两个用法刚好相反，前者是用A代替B,后者是用B代替A,其中substitute for 的for后面接的是被顶替的东西。这个怎么理解呢？设想一下如果谁B病了不能参加比赛，要找个人A顶替，那肯定是A for B.

replace ...with...这个就比较容易理解，因为中国人都对with的用法很清楚。
第二种是直接用替代物做主语:A substitute for B或者A replace B,两者用法完全一样。

这样说来，substitute for 和 replace的区别也不大。

我们还是来看上面的例句They were substituting violence for dialogue。如果改写成replace就是。

They were replacing dialogue with violence.

替代物做主语就是：Violence were substituting for dialogue.

或：Violence were replacing dialogue.或Dialogue were being replaced by violence. 

要注意，substitute 还可以做名词，是替代者、替补的意思。而replace还可以做“把。。。放回原处”的意思（这才是replace构词法re-+place的本来意义），不过这种用法比较少而已。