Publicity requirement: concepts are shareable (quotes Frege 1948, Fodor 1998, Prinz 2002)
Externalism- concepts can be contributed to by facts/causes without awareness
Internalism- Denies this
Argument here is that publicity req. mitigates against accepting the internalist view.
Problem - changes in external content alone do not affect behavior; internal content does.
So it isn't possible to have a theory of concepts which - has concept identity across persons - explains publicity behavior
Similarity may provide an escape, if not circular