Mathematics and the World

Maybe this is how to say it:

What we find is not that there is some mysterious isomorphism between certain mathematical structures and 'the world'; but that there is a quite intelligible isomorphism between these structures and the tacit (or even explicit) 'grammar' (in the Wittgensteinian sense) of any descriptions of the world that we find we can agree about.

It isn't that the world is mathematically structured in some imponderable way, but that we cannot describe it without using mathematics.  And our descriptions come to us so naturally (as competent language users) that we think they, themselves, are isomorphic with some 'phenomenological' structure (our internal sensory and cognitive environment) which seems (to us) to produce them.  We forget that we do not share these phenomenological environments, except in the sense that we succeed in sharing our descriptions; communicating our 'observations'.