The problem is that no one ever bothers to define what it means to "exist".
I'ld say that those things that have some kind of measurable, or otherwise objectively detectable, manifestation are things that I would label as "existing".
Everyone assumes that a "tree" exists, but does the idea of a tree exist?
I don't need to "assume" that trees exist. I'm looking at one right now in front of my office.
And if it doesn't then how did we identify the existence of the thing we're calling a "tree"?
It's right there, in front of my office.
Measurable, detectable, quantifiable.
How did we differentiate it's existence from the existence of everything else around it and from which it's existence springs?
Observation.
My buddy also witnessed first hand how very existing trees are, when he smashed into one with his car.
In fact, it would seem that the idea of a tree existing must exist before the tree, itself, can.
That makes no sense to me.
However, there certainly are things that only were defined in theory before they were established in practice.
Like atoms. Atomic theory was a thing long before we were able to directly observe atoms. Didn't stop us from splitting them open and harnessing the power that came out of it and releasing it into a nuclear explosion though. So that by itself was also a form of objective detection.
The atom was purely theoretical. But the theory had so much evidence that people assumed its accuracy. And clearly they were correct.
As without the idea of the tree existing the tree is just a lost bit of the total mass of undifferentiated existential phenomena.
No idea what you mean by that.
What really defines a 'materialist' from an 'immaterialist' is the acceptance of idea as fundamental existential phenomena (the realm of existence called "metaphysical").
Then I'm a materialist.
What you said there, seems to me to be nothing but a fancy way of saying that "immaterialists" just imagine things and then assume those imagined things to be actually real.
The materialist chooses to believe that ideas don't 'really' exist.
That's nonsensical.
Obviously ideas exist. But they exist as thoughts only. They don't have objective existence in the outside world.
btw: I think you are being a bit confusing with the word "idea". Isn't "concept" a better term for what you are talking about?
That only the matter and energy that creates the idea exists. While the immaterialist understands that without the idea of "existence" (and a great many other ideas), nothing exists but an uncognated phenomenl soup. Within which the whole question of what exists and what doesn't can't even be asked.
Again, I have no idea what you are trying to say here.