Q & A

Are you quite sure it was your brother?
Absolutely!

How did everything go?
It went well, thank you.

How can we get hold of a video recorder before the meeting tomorrow?
Leave it to me. I know someone who can help.

May I wait inside?'
Surely. (used to answer a question) yes; indeed

Shall we go on Thursday instead of Friday?
That's a thought. (that's a good idea)



I think not! In British English, I don't think so. and I think not. are both used, although they have different nuances.
* I don't think so. is more common, and shows a little diffidence or uncertainty.

A: Is it going to rain today?
B: I don't think so. I'd just wear a t-shirt if I were you.

* I think not. is used to disagree emphatically.

A: You still owe me.
B: I think not! If I hear any more from you about this, you'll be hearing from my solicitor.

Sorry, but I don't have any references I can cite. Just my personal experience.