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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:
- Intentions pose problems for agents, who need to determine ways of
achieving them.
- Intentions provide a `filter' for adopting other intentions, which
must not conflict.
- Agents track the success of their intentions, and are inclined to
try again if their attempts fail.
- Agents believe their intentions are possible.
- Agents do not believe they will not bring about their intentions.
- Under certain circumstances, agents believe they will bring about their
intentions.
- 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:
- It has a goal that eventually becomes true, and
believes that is not currently true.
- 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