A logical approach to the dynamics of commitments

Abstract

In this paper we present a formalisation of motivational attitudes, the attitudes that are the driving forces behind the actions of agents. We consider the statics of these attitudes both at the assertion level, i.e., ranging over propositions, and at the practition 2 The term `practition' is due to Castañeda [6]. 2 level, i.e., ranging over actions, as well as the dynamics of these attitudes, i.e., how they change over time. Starting from an agent's wishes, which form the primitive, most fundamental motivational attitude, we define its goals as induced by those wishes that do not yet hold, i.e., are unfulfilled, but are within the agent's practical possibility to bring about, i.e., are implementable for the agent. Among these unfulfilled, implementable wishes the agent selects those that qualify as its goals. Based on its knowledge on its goals and practical possibilities, an agent may make certain commitments. In particular, an agent may commit itself to actions that it knows to be correct and feasible to bring about some of its known goals. As soon as it no longer knows its commitments to be useful, i.e., leading to fulfillment of some goal, and practically possible, an agent is able to undo these commitments. Both the act of committing as well as that of undoing commitments is modelled as a special model-transforming action in our framework, which extends the usual state-transition paradigm of Propositional Dynamic Logic. In between making and undoing commitments, an agent is committed to all the actions that are known to be identical for all practical purposes to the ones in its agenda. By modifying the agent's agenda during the execution of actions in a straightforward way, it is ensured that commitments display an intuitively acceptable behaviour with regard to composite actions.