A discussion of Goodwin

In 1993 Richard Goodwin wrote a paper entitled "Formalizing Properties of Agents" (Goodwin, 1993). In it, he tries to abstract away as much as possible, leaving only what is crucial to "agenthood". The work is summarised here (extremely briefly) partly because it is an excellent basis for discussion and partly because some of the questions Goodwin doesn't answer are very interesting leads into other aspects of agency.


Goodwin's formalism requires an agent, a task and an environment. Most of the paper is devoted to agents and tasks; the environment is rather brusquely dismissed as "everything present before the agent was built", with the agent being "everything that was added". More on this later.

Goodwin begins with a very simple working definition of agency: "an agent is an entity created to perform some task or set of tasks".

He divides agents into two classes, general and deliberative. He states that for agents in general, the only meaningful approach is the behavioural approach, that is, defining and describing agents in terms of what they do, without ascribing internal states of any kind. Deliberative agents are those which contain an internal model of the world (including the agent itself) and act based on the state of that model. The state of the model is modified over time according to sensory input and in response to the agent's own actions.

The fundamental properties of an agent in Goodwin's terms are that such an entity be capable, perceptive and successful. Capable means able to affect its environment in ways that will allow it to accomplish its task, that is, having suitable effectors. Perceptive means able to perceive its environment in ways that allow it to bring its effectors to bear in order to accomplish its task. Successful means effective in accomplishing its task. To these three, he adds reactive (meaning to be able to respond to events in the world swiftly enough to be successful) and reflexive (meaning responding in a stimulus/response fashion).

To the five general properties given above, Goodwin adds for deliberative agents predictive, interpretive, rational and sound. Predictive means able to predict how it can achieve its task, based on an internal model of the world (environment). Interpretive means able to correctly use its sensor readings, and rational means that the agent chooses to do those things that it predicts will achieve its goals. Sound is simply the state of being predictive, interpretive and rational.

Goodwin begins by defining these properties in a binary fashion (an agent that is/isn't successful, is/isn't capable and so on) then extends the definitions into a relative framework to allow comparisons between agents. This is done by introducing the concept of a utility function which allows "success' to be compared - from this flow the other comparisons. For example, one agent is more capable than another if it is more successful ("has higher utility") in the same environment than the other.


The relationship between agent and environment is unsatisfying in Goodwin's formalism. Defining the environment as whatever was there before the agent was built is uncomfortably akin to describing the art of sculpture as removing all the marble that doesn't look like the subject.

While Goodwin implies that all agents exist in order to effect changes of some sort in their environment, he never actually states this.

A housebrick could be an agent within Goodwin's formalism: The surfaces of the brick are its effectors. Its task is to not compress, that is, its task is to hold other objects apart (presumably other bricks). Its sensors are non-existent - sufficient, but degenerate. It is reflexive in that it responds to the "stimulus" of pressure by resisting collapse, though this is a somewhat long bow! The brick could even be seen as a deliberative agent, with a degenerate internal model of the world, though it seems (slightly) more satisfying to consider the brick a reflexive agent.

The properties "successful" and to a lesser extent "capable" provide admirably well for a sliding scale; Goodwin in fact wishes his formalisation to provide a basis for comparing the performance of agents performing the same tasks in the same environment. A sliding scale needs extremes, and perhaps the brick is one extreme. The only escape seems to be the tenuous requirement that "success means total success" - since the brick performs its task indefinitely, we have no way of knowing that it hasn't succeeded unless it actually eventually succumbs to pressure and collapses (or is removed from duty). Until then we can only say "so far, so good...".

This same comment would appear to apply to any task falling into the class of tasks Goodwin refers to as "tasks of maintenance", that is, tasks where the agent must "maintain some condition in the environment". The example Goodwin gives is an agent controlling room temperature. This could be avoided by modifying the formalisation so that such tasks are defined as sequences of tasks, each to be achieved within a set period. However, it seems to me that allowing a housebrick status as an agent, even as a degenerate case, is a weakness in this formalism.

There seems to be some ambiguity in Goodwin's formalism regarding the place of humans. Firstly, theological arguments aside, it does not seem obvious that humans are created to accomplish specific tasks (Goodwin's fundamental definition). Secondly, Goodwin specifically limits his model to "simple deliberative agents" which do not learn. That is, they can alter the state of their internal model, but not the model itself. However in defining a non-deterministic environment, Goodwin postulates agents with free will (presumably humans) as part of that environment.

On the whole I suspect that Goodwin does not intend his formalism to apply to humans, though humans are part of the environment within which he expects agents to operate. The ambiguity arises from a statement of purpose ("...created to perform...") without any statement of the source of that purpose.

 [previous]  [index]  [next]
Email me!
Last modified 16 December 1995, 23:45
© Copyright 1995 Karl Auer