Communication Attitudes: A Formal Account of Ostensible Beliefs and Intentions

Conventional approaches to the modelling of autonomous agents and agent communication rely heavily on the ascription of mental properties like beliefs and intentions to the individual agents. While indeed very powerful, these “mentalistic” approaches are largely incompatible with the concept of open environments populated by truly autonomous, self-interested (greyor black-box) agents. We propose dynamic, revisable ostensible beliefs (or opinions) and ostensible intentions as a sound basis for the external description of agents from observable communication processes. Apart from providing a very natural semantics of communicative acts exchanged between rational agents, this allows e.g. for the simultaneous reasoning about mental and communicated attitudes without blurring interferences, and a fine-grained, statement-level concept of trust. Another potential application is in modelling multi-source (i.e. social) opinions, allowing for the computational representation of semantically heterogeneous, possibly inconsistent knowledge in a socially reified form, and a probabilistic weighting of possibly indefinite and inconsistent assertions attributed to different provenances. What distinguishes an agent’s communication attitude of opinion (ostensible belief) from her mental attitude of belief is that the former is triggered and revised by social conditions, more precisely communicative acts and underlying social structures like legal, organisational and economic laws. While these opinions might as well reflect the true beliefs of benevolent, trustworthy agents (an assumption that is made by certain traditional approaches to agent communication semantics), this should be considered a special case for autonomous, self-interested agents in open systems. Also, uttering an opinion doesn’t necessarily mean that the agent truthfully intends to make someone adopt this opinion as a belief. Instead, opinions emerge from (more or less hidden) agent intentions and social processes, they are tailored to the intended communicative effect and to the opinions and ostensible intentions of the audience. Thus, concepts like perception, epistemic logic, knowledge acquisition, belief revision, etc., which are devoted to the acquisition and maintenance of truthful and consistent information, do not necessarily apply to opinions. In analogy to opinions, an ostensible intention is a communication attitude denoting that the intention holder allegedly commits herself to striving for some desired action or goal state. This may include getting another agent to perform a desired action. Just like opinions, ostensible intentions are part of the “public (or discourse) identities” of mentally opaque agents (whereby a certain agent can even exhibit several possibly inconsistent identities in different social situations), and they are thus in general not identical with any “true” intentions in the sense of earnest self-commitments [6]. To establish communication attitudes, we take the viewpoint of an observer who selectively overhears communication processes and models and revises a current “communication attitudes store” of the communication system. This observer can either be passive or one of the agents participating in the observed interaction. We associate opinions with social contexts (or “contexts” for short) which partially or fully describe the communicative state in which the respective attitude is maintained and provide expected (i.e., possibly uncertain) conditions for the initiation and termination of the respective attitude (its logical validity, respectively). The social conditions of attitudes can be modelled both logically and procedurally (using,