从前 and 以前can both be used alone to mean “before”,“formerly”, or “in the past” in an approximate way. Let’s look at some examples.
When used alone, these two words can also be used as attributives and are often put before a noun or pronoun to mean “something or someone in the past” or “formerly”.
We can put a time word or something that hints at a certain time before 以前,to mean “before that time”, but 从前 can't be used in this situation because it’s only used to show a rough idea of the past in general.