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Cohen and Levesque - intention

One of the best-known and most influential contributions to the area of agent theory is due to Cohen and Levesque [Cohen and Levesque, 1990a]. Their formalism was originally used to develop a theory of intention (as in `I intend to...'), which the authors required as a pre-requisite for a theory of speech acts [Cohen and Levesque, 1990b]. However, the logic has subsequently proved to be so useful for reasoning about agents that it has been used in an analysis of conflict and cooperation in multi-agent dialogue [Galliers, 1988a][Galliers, 1988b], as well as several studies in the theoretical foundations of cooperative problem solving [Castelfranchi et al., 1992][Castelfranchi, 1990][Jennings, 1992][Levesque et al., 1990]. Here, we shall review its use in developing a theory of intention.

Following Bratman, [Bratman, 1990][Bratman, 1987], Cohen and Levesque identify seven properties that must be satisfied by a reasonable theory of intention:

  1. Intentions pose problems for agents, who need to determine ways of achieving them.

  2. Intentions provide a `filter' for adopting other intentions, which must not conflict.

  3. Agents track the success of their intentions, and are inclined to try again if their attempts fail.

  4. Agents believe their intentions are possible.

  5. Agents do not believe they will not bring about their intentions.

  6. Under certain circumstances, agents believe they will bring about their intentions.

  7. Agents need not intend all the expected side effects of their intentions.
Given these criteria, Cohen and Levesque adopt a two-tiered approach to the problem of formalizing intention. First, they construct a logic of rational agency, `being careful to sort out the relationships among the basic modal operators' [Cohen and Levesque, 1990a]. Over this framework, they introduce a number of derived constructs, which constitute a `partial theory of rational action' [Cohen and Levesque, 1990a]; intention is one of these constructs.

The first major derived construct is the persistent goal. An agent has a persistent goal of iff:

  1. It has a goal that eventually becomes true, and believes that is not currently true.
  2. Before it drops the goal , one of the following conditions must hold: (i) the agent believes has been satisfied; or (ii) the agent believes will never be satisfied.
It is a small step from persistent goals to a first definition of intention, as in `intending to act': an agent intends to do action iff it has a persistent goal to have brought about a state wherein it believed it was about to do , and then did . Cohen and Levesque go on to show how such a definition meets many of Bratman's criteria for a theory of intention (outlined above). A critique of Cohen and Levesque's theory of intention may be found in [Singh, 1992].

Next: Rao and Georgeff Up: Theories of Agency Previous: Moore - knowledge
Fri Nov 4 16:03:55 GMT 1994