He will be earning only half as much as he used to. 

网友的两种理解都不对。

1. earning 的宾语是much，不需要添加 money 或换成 money，更不需要按定语来变换结构。简化结构后，实际为：

He will be earning much. 比较结构是：He will be earning as much as ....  继续演变下去，看第2条。

2. half 是“二分之一”，其实就是一个分数；“三分之一” 则说one third；“三倍” 则是 three times。放在比较结构之前分别是：

half as much as

one third as much as

three times as much as

这里，half,  one third,  three times 都是修饰as much的。是倍数表达法的一种。

3. 如果分数或倍数放在名词前，则用作前位限定词。如：

This bridge is three times the length of that one.这座桥是那座桥的三倍长。