Wanikani has 以前 translated to “previously, before” and 以後 translated to “after this, from now on, after, since”. From the kanji it seems as though these vocabulary are essentially opposites. Would I be remiss in adding “before this” as a user synonym to 以前?
Wanikani calls both vocabulary “nouns”, but wiktionary calls 以後 an adverb. In fact, wikitionary has completely different translations from wanikani for 以前: 1. “(the one) before”, “formerly”, “ago”. (This is also confusing because “formerly” is also an adverb!)
Could someone help shine light on the “true” translations for these?