Hi Simone. Not being at all an expert in language, I would just give you my mulling over the case of demonstrative you're bringing up with the difference between this and that.
The roots of such words could be found out - in my opinion - two ways: 1. As being a "real being" you exist in the space and the time. 2. As a human being you have to show (de-monstrare) and speak over what you show. (Animals probably are well aware of space relationships but don't speak about it.) One doesn't like spliting hair at any time. So one doesn't always precisely measure the distances in space, but one roughly makes out what is near from what is far. To point at something which is near, one says "this" (pronoun, adjective or adverb). To point at something which is far, one says "that".
Uttering "i" (sound "e" in English) suits better for what is near. Try it for size: imagine you get nipped at your skin or you get at a pitch of orgasm. Uttering the "a" of that is quite broader in your throat, broader thus larger thus farther, more relax in a good mood, more stronger in a bad mood.
As we know that space and time are nothing but parameters of one unique reality, this and that are also used to point respectively at what is near and far in the time, this for immediate past or future, that for the opposite.
As we speak in space and time, we also use this and that to point at something said near or far in the discourse. "This" for what has been just mentioned, or for is about to be said as well.
A lot of psychological speculations are to be pulled off this and that. For instance suppose you are offered brownies with your five o'clock tea. Being hungry and fond of brownies, you might say "I love THESE brownies" (these being plural of this). Being fed up and hating such cakes, you would rather say "I hate THAT".
"This" opposed to "that" often comes first: "this and that"(ceci et cela) but not always, because as we can go away, we can come back as well. So I might say: He ran that way and this (like in French, il allait et venait).
Thanks to you, Simone, this and that turned philosophical prompts to me. Mind you, this is just my whim.
From Simone Bennahmias: Différence between this and that