In his book Principe de diplomatie, Alain PLANTEY states that: "Diplomacy is often considered a subtle and random art, combining skill, dissimulation and tactics. It calls on the imagination, observation and skill of those who practice it, and cannot therefore be reduced to compliance with theoretical rules, the addition of information or the application of legal considerations. It also includes a large proportion of recipes and customs established by experience, methods and conventions, whose observance influences the chances of success. This explains the types of behavior, elocution, discipline and even reasoning that Diplomats generally adopt, and which constitute a kind of international code of the profession". However, with the paradigm shifts confronting state bilateralism since the end of the First World War, PLANTEY’s view had become obsolete. The diplomatic function has undergone mutations throughout the ages. Today, modern diplomacy is based on a combination of openness to public opinion, the extension of the sphere of influence of the state, and the development of a new and more effective diplomacy.