表示目标或方向的区别
两者均可表示目标、目的地、方向等，此时也要根据不同动词分别对待。如：
在 come, go, walk, move, fly, ride, drive, march, return 等动词之后通常用介词 to 表示目标或目的地。如：
He has gone to Shanghai. 他到上海去了。
They walked to a river. 他们走到一条河边。
在 leave, start, set out, set off, sail, head 等动词之后，通常用介词 for 表示方向。如：
He left [started] for Beijing. 他动身去北京了。
They set out [set off] for home. 他们动身回家了。
Our ship will sail for Shanghai tomorrow. 我们的船明天开往上海。
注：在某些名词之后也通常用介词 for(有时也用 to) 表示方向或目的地。如：
Is this the train for [to] Paris? 这是开往巴黎的火车吗?
Passengers for Oxford must change at Didcot. 前往牛津的旅客必须在迪德考特换车。
They were well down in front. 他们坐得很靠前。
Sales are well up on last year. 销量比去年大幅增加。
He leaned well forward in his chair. 他坐在椅子上身体很向前靠。
The house is set well back from the road. 这座房子离公路挺远。
Take my tip and keep well away from that place. 听我的劝告，离那个地方远远的。
在某些习语中的区别
在某些结构中 to 和 for 都可用，但含义截然不同。如：
answer to 符合 answer for 保证
make up to 巴结 make up for 弥补
go to him 到他那儿去 go for him 去迎接他
thanks to 多亏 thanks for 多谢
修饰情态动词
能用well加强语气的情态动词主要是can, could, may, might。如：
can well：意思是“完全能够”“完全可以”“有充分理由”。如：
She can well answer such questions. 她完全能够那样的问题。
I can well understand how sorry he was then. 我能充分了解当时他是如何地难过。
could well：意思是“很可能”“完全能够”“有充分理由”。如：
The crisis could well place the relationship at risk. 这场危机可能会使这一关系有破裂的危险。
This election result could well lead to further bloodshed. 这个选举结果很可能导致再发生流血冲突。
She could well afford to pay for the reception herself. 她能够很容易自己支付招待会的费用。
注意句式It could well be that…（很可能……）。如：
It could well be that he has a real vocation. 很可能他是找到了自己真正的使命。
It could well be that rich people treasure peace more highly than poor people. 很可能富人比穷人更珍惜和平。
My book, The House of Hades, is missing. Who ________ have taken it?
A.need
B.must
C.should
D.could
--Why are your eyes so red? You ________ have slept well last night.
--Yeah, I stayed up late writing a report.
A. can't
B. mustn't
C. needn't
D. won't
