by now表示的意思為到目前為止，但是后面沒有要加消極信息的那一層意思,也沒有嚴格的時間點或地點的要求；so far意為如此程度、迄今為止，表示時間點或地點，后面的句子一般用完成時。

by now例句

She'll have had the results by now.

她現(xiàn)在應該知道結果了。

She would be in bed by now, as like as not.

這工夫她很可能睡了。

If you think about it, those children must be at school by now.

想想吧，那些孩子現(xiàn)在一定在學校了。

He'll be home by now.

他現(xiàn)在該到家了。

If he started out at nine, he ought to be here by now.

他如果九點出發(fā)，現(xiàn)在應該到這里了

so far例句

How many driving lessons have you had so far?

你到目前為止上過多少節(jié)駕駛課了？

So far, the police investigation has drawn a blank.

到目前為止警方的調查毫無結果。

What do you think of the show so far?

到目前為止你覺得這場演出怎么樣？

I've only read a little of the book so far.

這本書我才讀了一小部分。

That's the truth, in so far as I know it.

就我所知，那是真實情況。