- The brain is constructed entirely of ingested matter.
- Knowledge inheres in the brain.*
- So knowledge inheres in (metabolised) food.
- Food, like all matter, is noumenal, of the external world.
- So the mind inheres in the external world.
- So there is no metaphysical barrier between mind and world.**
- So there is no high-level puzzle about knowledge.***
* Yes, not just in the brain, but this suffices.
** Clearly this does not defeat the radical sceptic in her original, Cartesian internalist problematic. But the best candidate for a philosophical fact is: nothing can. Their simple, hard-reset reply is just: "it's an epistemic barrier, not a metaphysical one".
*** All this leaves to solve are the smaller titanic mysteries of consciousness, phenomenal binding, meaning, apriority, most of the highly unfinished fields neuroscience, cognitive science, behavioural genetics ...