Here's my latest working definition of public diplomacy.
The purpose of public diplomacy is to identify, empower, encourage (and possibly equip) self-organizing systems. The self-organizing systems engaged should be those that currently or potentially support, directly or indirectly, the foreign policy objectives of the public diplomacy-sponsoring actor. The support networks of groups that oppose or compete with the same foreign policy objectives should also be engaged as minds can be changed.
Your comments are appreciated.