> I wouldn't say that being found in nature means that something is not made up.
Then define "made up".
> For all I know the noumenon could be dealing in something else entirely, and math might just be a really useful tool we came up with (like classical physics, and probably modern physics).
Suppose it is merely a useful tool. This tool then necessarily has a structure that's isomorphic to part of the structure of the noumenon, otherwise it wouldn't actually be a useful tool.
Therefore, whatever structure it models is itself mind independent, as I said. The symbols and formalisms we use are interchangeable, but the structure revealed is not.
Then define "made up".
> For all I know the noumenon could be dealing in something else entirely, and math might just be a really useful tool we came up with (like classical physics, and probably modern physics).
Suppose it is merely a useful tool. This tool then necessarily has a structure that's isomorphic to part of the structure of the noumenon, otherwise it wouldn't actually be a useful tool.
Therefore, whatever structure it models is itself mind independent, as I said. The symbols and formalisms we use are interchangeable, but the structure revealed is not.