"so far" vs "as yet"

"so far" vs "as yet"

引文:Longman ONLINE
far (adv)
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7. 'so far' also 'thus far'(formal)
until now 到目前為止 (已發生但後來卻改變了沒有消息了)
Ex: So far we have not had to borrow any money. <-- 否定句
Ex: SO far I have never seen her.
Ex: They're delighted with the replies they've received from the public thus far.

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yet (adv) 迄今為止(未發生)
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5. 'as (of) yet' used when saying that something has not happened up to now:
Ex: We've had no luck as yet.
Ex: on an as yet undecided date.
EX:As yet, we have received no answer.