I think they mean existence in general, not the existence of any specific thing. Meaning that if there were no “existence” then we wouldn’t be here to consider its nonexistence.
> I think they mean existence in general, not the existence of any specific thing.
Yes, but the definition of "existence" doesn't require that anything must actually exist.
In other words, it is not the case that existence "cannot not exist by definition."
> Meaning that if there were no “existence” then we wouldn’t be here to consider its nonexistence.
That's an anthropic principle argument, which is not an argument from the definition of existence. One of the premises of that argument is that we exist already.
How can nothingness exists, if it is supposed to not exist since it is nothingness?
Concept are not really for humans, but humans can grasp them. Or would you say that the sun only exists because (some) humans see it?
It's not because a human is unaware of something that it does not exist. Its concept is still there somewhere. Independent of its treatment by human cognition.
