Zhiqian, yiqian and congqian

之前／以前／从前

以前 can be translated as Before, 从前 is usualy used when telling a sotry, so it means „Once upon a time“. They have similar meanings, but the general rule is, that 以前, can be always used also to replace 从前, but 从前 can be used only in a specific situations.

从前 can be used only if it stands alone and can not be acompanied by another time expresion.

There used to be a castle before.

对 － 从前在这里有一座城堡。

对 － 以前在这里有一座城堡。

There was a castle two years ago.

对 － 两年以前这里有一座城堡。

错 － 两年从前这里有一座城堡。

以前／之前

以前／之前 can be alo used as a definition of a time in a future as well as in a present. 从前 does not have this usage. For Example:

对 － 我想明天两点以前走。

错 － 我想明天两点之前走。

错 － 我想明天两点从前走。

The difference between 之前／以前 is very easy. 之前 expresses longer time.

以后／后来

后来 can express only past. 以后 can express also present or future.

对 － 本来他以为不喜欢吃，后来他吃了一口，就无处不吃。

对 － 本来他以为不喜欢吃，他吃了第一口以后就无处不吃。

对 － 我明天下班以后去接她。

错 － 我明天下班后来去接她。

后来 can stand alone. 以后 can not. It must be accompanied by a time expresion.

对 － 我以前在Intel工作，后来就去了Microsoft。

错 － 我以前在Intel工作，以后就去了Microsoft。

后来／然后

后来 is a noun, 然后 in a conjuction

后来 can express only past events

然后 can express also present as wel as future.

然后 is not used to express time, but to express continuity of some actions. It is often used in combination with „First (than)“,

我吃了饭，然后去了酒吧。

实用对外汉语教学语法(pp. 54) 对外汉语教学语法释疑201例 (pp. 3, 5, 7)