当表示“至于”这个意思时，as for，as to都可以用，一般位于句首，但as for常含有贬义；当表示“关于”，后跟whether、when、what、where、how等引导的从句时，只能用as to，有时as to可省略。这种用法上的as to一般位于句中。
as to和as for区别
1、as for在语体上不如as to 正式，并且着重话题的转换，也就是说，它所引导的是前面尚未提到过的新的事情，因此，它不能用于文章的开头。
例句：As to that, I haven’t decided yet.此时用于句首，不能用as for。关于那件事，我尚未做出决定。
2、as to常常与wh-疑问词引导的动词不定式和名词从句连用（有时可省略），而as for却没有此种用法：
例句：Nobody could decide as to)what to do.谁也不能决定该做什么。
as for的含义及用法
as for意为至于，就…方面说来。引导时间状语从句。主句可以是主动句，也可以是被动句。
例句：As for avoiding you, nothing could be further from my mind.
至于说躲避你，我根本就没有这样的想法。
As for his job — well, he was very mysterious about it.
至于他的工作，他总是显得非常神秘，从不多说。
As for doctors, when you go to see them they just look right through you.
说到医生，你去看病时，他们直把你当透明的。
As for anything told to me in confidence, well, my lips are sealed.
至于私底下告诉我的任何事情，我会守口如瓶的。
As for Laura and me, the colour of our skin has never mattered
至于我和劳拉，肤色根本不是问题。
As for her engagement with Adam, I would say the portents are gloomy.
至于她和亚当的婚约，我看兆头不妙。
As for the present, things are far better than at any time in the past.
如今呢，可比以往任何时候都要强。
