What Are Plans For?

What plans are like depends on how theyre used. Two views of plan use are contrasted. On the plan-as-program view, plan use is the execution of an effective procedure. On the plan-as-communication view, plan use is like following natural language instructions. We have begun work on computational models of plans-as-communication, building on our previous work on improvised activity and on ideas from sociology. The plan-as-program view and the plan-as- communication view offer very different accounts of the role of plans in activity. The plan-as-program view gives plans a central role. Plan use is only a matter of execution, performed by a simple, fixed, domain-independent interpreter. Plans-as-program directly determine their users actions. The plan- as-communication view gives plan a much smaller role. It requires an account of improvisation. Plans, on this account, do not directly determine their users activity. Indeed, an agent can engage in sensible, organized, goal-directed activity without using plans at all. An agent who does use a plan-as- communication does not mechanically execute it. Instead, the agent uses the plan as one resource among others in continually redeciding what to do. Using a plan requires figuring out how to make it relevant to the situation at hand, a process of interpretation which can be arbitrarily complex.