hitherto vs so far

hitherto and so far both are adverbs.

Word	Noun	Adjective	Verb	Adverb
hitherto	No	No	No	Yes
so far	No	No	No	Yes

As adverbs, hitherto and so far are synonyms defined as:

hitherto and so far: used in negative statement to describe a situation that has existed up to this point or up to the present time

Other synonyms of hitherto include as yet, heretofore, thus far, til now, until now, up to now, yet.

hitherto (adverb)	so far (adverb)
used in negative statement to describe a situation that has existed up to this point or up to the present time	used in negative statement to describe a situation that has existed up to this point or up to the present time
	used after a superlative
	to the degree or extent that