John Brown, formerly of the Public Diplomacy Press and Blog Review, wrote a terrific short discussion of the differences between public diplomacy and propaganda. I recommend you read it.
At its best, public diplomacy:
- Provides a truthful, factual exposition and explication of a nation’s foreign policy and way of life to overseas audiences;
- Encourages international understanding;
- Listens and engages in dialogue;
- Objectively displays national achievements overseas, including in the arts.
At its worst, propaganda:
- Forces its messages on an audience, often by repetition and slogans;
- Demonizes elements of the outside world;
- Simplifies complex issues;
- Misrepresents the truth or deliberately lies.
Both public diplomacy and propaganda, at their best or their worst, can achieve credibility with their audiences. However, the best public diplomacy achieves credibility through careful presentation of fact and thoughtful argumentation, while the worst propaganda achieves credibility by falsification and sensationalism. As a rule, public diplomacy at its best, which appeals to the intellect, is believed in the long run, while propaganda at its worst, which inflames atavistic emotions, is believed only for short periods. The best public diplomacy convinces audiences that its content and purpose mesh, and that therefore it is honest; the worst propaganda leads audiences to believe that its contents do not reveal its true purpose, and that therefore it is dishonest.