We learn math by being schooled in math.
School
is the world.
Not by observing the world.
So then who taught the first person that knew math?
They are outside of the brain but only as elements of the numbers that we think of.
What does that mean?
I have explained this many times.
The brain accepts an input from outside of the brain. The input triggers a process. The process is what we think.
Again, real quantities may have been the catalyst for the invention of numbers and even some basic functions like addition and subtraction.
But the invention is not a reflection of the world. Like abstract art it is a transformation of elements of the world, in a mind, into something not in the world.
Whether you like it or not, this is dualism.
I don't know why you won't admit it. If I had to guess, it's because dualism has religious connotations. But it doesn't when studying philosophy. I am sure that many atheists were dualists, not to say that you are an atheist.
Science is showing us that reality is probably monistic, or it is at least showing us that there is no reason to believe in a dualistic nature from the observations made thus far.
I explained this 6 times today; see posts: #2966, #2970, #2974, #2976 (twice), #2980. This is madness!
Talking about some mind body dualism isn't coming close to answering my questions.
You say numbers exist in the world.
No, I keep saying that elements of our thoughts of numbers exist in the real world. Just like we have no idea what a banana actually is, I have no idea what these inputs into the brain are.
How do you get from 3 coconuts to just plain 3 without a mental transformation?
You are assuming some kind of platonic realm. That's fine, but it's not science and there is no evidence of such a thing.
Again, you seem to think humans can only reflect the world. They have imagination and can invent things not ever in the world.
No, I don't think that humans only reflect the world. But I argue that every thought is a complex process involving some element of the environment.