Plans and situated actions – The problem of human-machine communication

This post is part of a series of notes I collated during my studies at UCL’s Interaction Centre (UCLIC).


The organisation and significance of human action lies in plans. This view of purposeful action is the basis for traditional philosophies of rational action and behavioural science.

Plans are prerequisite to and prescribe action at every level of detail.

Those who adopt the planning model as a basis for interaction between people and machines draw on 3 related theories about mutual intelligibility of action:

  1. The planning model itself, which takes the significance of action to be derived from plans and identifies the problem for interaction as their recognition and coordination.
  2. Speech act theory, which accounts for the recognisability of plans or intentions by proposing conventional rules for their expression.
  3. The idea of shared background knowledge as the common resource that stands behind individual action and gives it social meaning.

A plan is a sequence of actions designed to accomplish some preconceived end. The model posits that action is a form of problem solving, where the actor’s problem is to find a path from some initial state to a desired goal state, given certain conditions along the way.

Actions are described, at whatever level of detail, by their preconditions and their consequences.

In problem solving systems, actions are described by (Allen, 1984):

  • Prerequisites – that which must be true to enable the action.
  • Effects – that which must be true after the action has occurred.
  • Decomposition – how the action is performed, which is typically a sequence of sub-actions.

The planning model attempts to bring concerted action under the jurisdiction of the individual actor by attaching to the others in the actors world sufficient description and granting to the actor sufficient knowledge that he/she is able to respond to the actions of others as just another set of environmental conditions. The problem of social interaction, consequently, becomes an extension of the problem of the individual actor.

The problem for interaction is to recognise the actions of others as the expression of their underlying plans.

The ‘same’ action as a matter of intended effect can be achieved in any number of ways, where the ways are contingent on circumstance rather than on definitional properties of the action.

Although an action can be accounted for post-hoc with reference to its intended effect, an action’s course cannot be predicted from knowledge of the actors intent, nor can the course be inferred from observation of the outcome.

  • Causal definition of action – i.e., the pre and post conditions that must hold to say the action has occurred, independent of the method.
  • Action’s characterisation – a particular method or procedure for the accomplishment of an action.

Throughout the process of plan attribution, the problem to be solved by the subject remains ‘ill informed’. At any given time, neither the range of possible plans that the other might be carrying out, nor the criteria for accessing just what plan is actually in effect, are clearly defined.

Plans are a constituent of practical action, but they are constituent as an artefact of our reasoning about action, not as the generative mechanism of action.

The planning model takes over our common-sense preoccupation with the anticipation of action and the review of its outcomes and attempts to systematise that reasoning as a model for action while ignoring the actual stuff, the situated action, which is the reasoning’s object.

An action’s significance seems to lie in as much in what it presupposes and implies about its situation as in any explicit or observable behaviour.

What we do and what we understand others to be doing is informed by assumptions about the person’s significance.

For cognitive science, the background of action is not the world as such, but knowledge about the world.

The claim is that our knowledge of the everyday world is organised by a “predetermined, stereotyped sequence of actions that define a well-known situation” or script.

Every situation, in other words, has its plan made up of ordered action sequences, each action producing the conditions that enable the next action to occur.

The normative order of these action sequences can be thrown off course by any one of distractions, obstacles or errors.

An obstacle to the normal sequence occurs when someone or something prevents a normal action from occurring or some enabling condition for the action is absent. An error occurs when the action is completed in an inappropriate manner, so that the normal consequences of the action do not come about.

Not only does the typical script proceed according to a normal sequence of actions, but also each script has its typical obstacles and errors that, like the script itself, are stored in memory along with their remedies and retrieved and applied as needed.

Whereas plans associate intentions with action sequences, scripts associate action sequences with typical situations.

Situated Actions

Every course of action depends in essential ways on its material and social circumstances.

The approach is to study how people use their circumstances to achieve intelligent action.

Five propositions:

  1. Plans are representations of situated actions.
  2. In the course of situated action, representation occurs when otherwise transparent activity becomes in some way problematic.
  3. The objectivity of the situations of our action is achieved rather than given.
  4. A central resource for achieving the objectivity of situations is language, which stands in a generally indexical relationship to the circumstances that it presupposes, produces and describes.
  5. As a consequence of the indexicality of language, mutual intelligibility is achieved on each occasion of interaction with reference to situation particulars rather than being discharged once and for all by a stable body of shared meanings.

1. Plans are representations of action

Plans are resources for situated action but do not in any strong sense determine its course.

Example ‘canoeists’ plan: “I’ll get as far over to the left as possible, try to make it between those two large rocks, then backferry hard to make it around that next bunch.”

A great deal of deliberation, discussion, simulation and reconstruction may go into such plan, but, however detailed, the plan stops short of the actual business of getting your canoe through the falls.

The purpose of the plan in this case is to orientate you in such a way that you can obtain the best possible position from which to use those embodied skills on which your success depends.

We generally do not anticipate alternative courses of action or their consequences until some course of action is already underway.

In many cases, it is only after we encounter some state of affairs that we find to be desirable that we identify that state as the goal toward which our previous actions, in retrospect, were directed ‘all along’ or ‘after all’. (Garfinkle, 1976).

2. Representation and breakdown

Although we can always construct rational accounts of situated action before and after the fact, when action is proceeding smoothly it is essentially transparent to us.

Situated action is not made explicit by rules and procedures. When situation becomes in some way problematic, rules and procedures are explicated for purposes of deliberation and the action, which is otherwise neither rule-based no procedural, is then made accountable to them.

3. The practical objectivity of situations

The environment of our actions is made up of a succession of situations that we walk into and to which we respond.

4. The indexicality of language

Our shared understanding of situations is due to the efficiency of language.

Language takes its significance from the world, whilst also transforming the world into something that can be thought of and talked about.

5. The mutual intelligibility of action

Language is not only anchored in but also constitutes the situation of its use.

We walk into a situation, identify its features and match our actions to it. This implies that, on any given occasions, the concrete situation must be recognisable as an instance of a class of typical situations and the behaviour of the actor must be recognisable as an instance of a class of appropriate actions.

Rather than actions being determined by rules, actors effectively use the normative rules of conduct that are available to produce significant actions.

References and further reading

  • Suchman, L. A. (1987). Plans and situated actions: The problem of human-machine communication. Cambridge university press.
  • Suchman, L., & Suchman, L. A. (2007). Human-machine reconfigurations: Plans and situated actions. Cambridge university press.

Updated on: 15 February 2021

Are you building something interesting?

Get in touch