This paper describes a framework for the representation and interpretation of indirect speech acts, relating them to the politeness phenomenon, with particular attention to the Ccise of requests. The speech acts are represented as actions of a plcm hbreiry 2ind are activated on the basis of the presence of syntactic and semeintic information in the linguistic form of the input utterance. The speech act cuicdyzer receives in input the senicintic representation of the input sentence and uses the politeness indicators to chmb up the decomposition and generalization hierarchies of acts encoded in the librciry. During this process, it eliminates the indicators and collects the negated presuppositions (represented cis effects of the indirect speech act) that characterize the politeness forms. Some cycHc paths in the hierarchy allow the system to cope with complex sentences including nested politeness indicators. In the proper places of the hierarchy the semantic representation of the input sentence is converted into a domain action in order to start-up, when needed, the domsiin-level plan recognition process.

We ciaim mental models are a framework that allows to shed light on the phenomenon of presuppositions. A plan-based lexical representation for verbs, together with the effect of conversational implicatures that discharge possible mental models, are the key features of this proposal.