But in this case the brain's understanding is based on observation of the world external to the self, and supernatural beings by definition aren't found in nature. So reality is free of supernatural beings not only via observation but in principle.
I don't understand what you mean by "metaphysics" in this context.
Because of my second assumption (which you share, as the fact you post here demonstrates) I am indeed informed about the world (as are you). My parents were real. My grandchildren are real. My air, drink, food, shelter, society, amenities, are all real, and come from outside my self, and are all known to me through my senses, and are no less known to me because I can't claim perfect knowledge of them.
Those are in the category of unfalsifiable claims, along with pure solipsism, Last Thursdayism, and so on. As such, they don't satisfy the criteria necessary to be taken seriously by science.
I define blû 2 to mean doesn't exist, so by the power of this denition you don't exist and that is true and a fact.
You are doing magical thinking and woo-woo. Your thinking as a definition will not cause or determine the parts of the world not you to be either natural or supernatural. Learn to be skeptical of your own thinking.
Further the word "real" has not objective referent and is thus not objectively true. You are in effect nothing but a product of a subculture within Western culture, but you have only learned to doubt other cultures. Not your own.
So here we go again. "Seriously" is not objectively true. You are subjective and in effect unable to understand your own cognition as that. You take it for granted and make a value system of what matters to you. But what matters to you, is subjective and different from what matters to me.
So again your reasoning is subjective and in the end a case of this:
"Man is the measure of all things: of the things that are, that they are, of the things that are not, that they are not." Protagoras.
We are "fighting" a fight that is older than Christianity and you are on side of in effect dogmatic knowledge and I am a relativist.
So again. The definition of blü 2 is doesn't exist. Stop using words as magical as magical and learn to be as skeptical of your own subjectivity as you are of everybody else's.
In effect you are irrational if you think as your definition as a case of thinking can decide what the world independent of your experience. Read some Kant on the irrationality of doing positive metaphysics as knowledge. And learn to check your words: Real has not objective referent and not does seriously.
You are making this subjective system of yours and it doesn't register that it is subjective, because it makes subjectively sense to you. You are as subjective as some religious, who don't understand that they are subjective.
There are 3 positions:
The world is natural.
The world is supernatural.
That is unknown what the world really is.
You are so narrow in your cognition that you can only hold 2 first ones. That is your problem, not mine. I can't thinking for you and get you to understand the limitation of "playing" definition games. So again, blü 2 means doesn't exist.
As for what metaphysics means, you do philosophy, so you should know. Metaphysics means what the world is in itself as it exists. You are a metaphysical materialist. That is what it means. But that is a belief, because your thinking as per the definition of what think the world is, doesn't determine or cause the world to be, what you think it is.
Stop doing philosophy unless you can actually understand the difference between to world to you versus the world in itself.