so far 是常用的词组，表示“迄今为止”的意思；thus far在中学中不常用，它们什么区别呢？https://www.quora.com/Whats-the-difference-between-thus-far-and-so-far给出了答案：
They both mean until this point or until now (you can use them both for distance as well as for time.).
Both can be used in a figurative sense （比喻的，抽象的）.
They can both be used in negative and positive sentences.
So is there a difference? Thus far is more formal. You would use thus far in formal correspondence, legal material, contracts, in academic works.
So far is for emails and in conversations.