I know the use of "this" and "that". In the case of referring to ideas, I can't understand the use of "this" and "that". Here I give the rules taken from the site below: Sometimes, the difference between this and that is quite subtle. We often use this to refer to something (e.g. an idea or suggestion) that you are about to say and we use that to refer something that you just mentioned:
Let’s go to the cinema. What do you think about that?
What do you think about this? We could go to the cinema.
1a. "Let’s go to the cinema." here the event did not happen yet so why "that" used in the first example?
2a. "we could go to the cinema" here the event already has happened so why "this" used in the second example? source:http://www.nativespeakeronline.com/confusing-words/what-is-the-difference-between-this-and-that