thus far vs so far

thus far and so far both are adverbs.

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

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

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

thus far (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