A 'discourse' can be defined as a linearised structure of semantically related statements generated by a source ('speaker') and conveyed to an audience ('hearer') in order to achieve a specific 'communicative intention'(or goal). Thanks to the hierarchical and decompositional nature of the communicative goals, the AI planning technique has been successfully adopted by many researchers as a solution to the problem of automatic discourse generation.

However, planning a discourse that can persuade the audience about the validity (or fallacy) of a certain proposition requires the speaker to hypothesise and maintain an adequate model of the hearer's beliefs and inference. Moreover, generating sophisticated discourse plans requires the adoption of an expressive belief language, which usually contains mutual belief expressions, uncertainty, belief grounding and justification, and, in general, doxastic attitudes that are often semantically related by logical formulae ('inner-outer' belief axioms).

In this talk, I argue that a clear distinction between the formal model of speaker-hearer beliefs and the planning machinery which makes use of it, is needed for the realisation of complex, real-world persuasive discourse plans. The main results presented are:
1) an expressive, formal speaker-hearer belief language Lo (and related belief system) that allows the representation of uncertainty, defeasible justification, belief grounding, functional discourse relations and communicative intentions;
2) a set of (abstract) discourse planning operators (defined using Lo) encoding different strategies for sincere belief persuasion and undermining;
3) a sound and linear pre-processing algorithm which can be used to integrate 'inner-outer' domain axioms within a set of planning operators.

I also show how this approach has been applied to pre-process a set of inner-outer belief axioms into the given set of discourse planning operators, and how the results have been used by the 'IPP' planner to produce real examples of complex discourse plans. I conclude with some considerations on the limits and possible extensions of the solution presented, and by sketching possible future directions of my work.