Some propositions cannot be demonstrated BECAUSE they are TOO BASIC to ‘prove.’ Similarly, some things CANNOT BE DEFINED.
But circular definitions FAIL to define.
That is about as useless a “definition” as one can imagine.
We have no concept of nothing, because nothing has no content for us to conceive. It has no properties. We cannot say “Nothing has property P” nor can we say “Nothing is.” Nothing does not exist.
Parmenides says “Nothing IS NOT.”
And each of us has SOME IDEA about “nothing” or “the Nothing” as Heidegger calls it.
Nothing ISN’T either of those things, because they ARE something.
That sentence both makes sense and remains baffling.
Much like Socrates’ assertion “The Good is beyond Being.”
As is Being, Nothing, Existence, Essence, Substance.
Discursive proof is “closer to home” in that humans make use of it a lot, but we do not notice that it depends on things SO BASIC we don’t even think to question them.
Unless we’re insane. Or philosophers.