 Though externalism may (or may not) be incompatible with these internalist forms of physicalism, this should not be taken to imply that externalism is itself an antiphysicalist doctrine, for one might hold that although mental contents do not supervene on narrow physical properties, they do supervene on wide physical properties. There is no obvious reason for physicalism about the mind to require a creature’s mental properties to supervene on its narrow physical properties. (For discussion of the requirements on physicalism, see the entry on  physicalism.)