Can I use these pronouns as a reaction immediately after something was said or happened, in order to express my opinion?
- This is/was amazing.
- That is/was amazing.
- It is/was amazing.
And by the way, is it more appropriate to use "This" when using a noun instead of an adjective?For instance "This is madness" compared to "That's crazy".
Go with 'that' in every one of those cases or whenever you are making immediate reference to someone else's comment. Avoid 'it' unless 'it' is a dummy subject as is the case of "It depends" (it's raining, it's nice to see you, etc.) so, "that's a good point", but, "Well, now that you mention it." or "YEs, if you want to make a big deal out of it." When the topic at hand becomes the grammatical object, 'it'sounds more natural.
'This' often refers to ours; e.g. "This sounds like a question for Mr. Answers!"
Sometimes it's used as mine: "Ok, this is the situation (which I am going to share with you). We also hear 'here' very often in this case, e.g. "Ok, here's the deal:"
That refers to 'yours'or anything from beyond my perspective. Even if the person says, "Yes, exactly, that is what I'm saying...". That originated from my perspective, but right now I am pointing to the concept on your side, before bringing it 'back home'.
In discourse (not conversation) either may be used in some cases to refer back within the discourse itslef, eg. "This is the situation we are faced with, then." or "That is what me must consider." This means the topic I a presenting, whereas that refers back to 'that' sentence' earlier. 'Thus' fits in here (my comment)/there (the previous sentence, looking back) somewhere, too.
These is the plural of this, those the plural of that. In your example you could say in these cases or in those cases for the same reasons mentioned in the previous paragraph.
Finally, this and that have temporal value akin to now and then, e.g. in those days versus these days.
This and that work a little differently in certain situations as compared to languages with analogous terms, as you are clearly aware. (Good question, then ;)
