Beliefs are partly constituted by features of the environment. ....a notebook plays for one person the same role that memory plays for another. ...The information is reliably there, available to consciousness, and to guide action, just as belief is.
Gist of Idea
A notebook counts as memory, if is available to consciousness and guides our actions
A Clark / D Chalmers (The Extended Mind , §4)
This is the modern externalist approach to beliefs (along with broad content and external cognition systems). Not quite what we used to mean by beliefs, but we'll get used to it. I believe Plato wrote what it said in his books. Is memory just a role?
-: 'Analysis' [-], p.5