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behavior controlled by a goal as the scope of that goal. A goal that controls
behavior over a long time period is likely to be accomplished by calling upon
goals of smaller scope rather than by calling on elementary actions directly.
Such subordinate goals are called subgoals, and the dominant goal is their
superordinate goal. A superordinate goal can be either a top goal or a subgoal
to some other goal of yet greater scope. tracing the relations upward, make
tea might turn out to be part of throw a dinner party. There is no upper
limit on the scope of goals; consider achieve world peace. The goals that are
involved in performing a given task jointly form a goal hierarchy or goal
tree. 18
typically, all the subgoals to a given goal have to be accomplished for that
goal to be accomplished. to make tea, you have to boil the water and put tea in
the strainer and pour the water through the strainer. These subgoals are linked
by conjunction (“and”). From the point of view of the superordinate goal, it
might not matter exactly how any one subgoal is accomplished. A subgoal can
be associated with different ways of achieving it; you can boil water over an open
fire or on an electric store or in a microwave oven. These methods are alterna-
tives. There is no need to boil the water three times; once will do. Similarly, go to
dinner might entail tell X that we”ll meet him at the restaurant, but success in this
part of the dinner project does not depend on whether X is told face-to-face or
via fax, phone, pigeon post or texting; all that matters is that X is told, somehow.
Alternative methods for achieving a goal are linked by disjunction (“or”). A goal
tree consists of alternating conjunctive and disjunctive layers; multiple subgoals,
each reachable by alternative paths, each of which in turn poses multiple sub-
subgoals, and so on. in everyday parlance, we refer to such a structure as a plan;
see Figure 6.2. The claim is that battle plans, business plans, lesson plans and
travel plans all share these structural features. The computer science term AND/
OR tree is awkward but descriptive of these complex structures.

task Environments

When a person decides to pursue a particular goal he is in the initial state of
his performance. A situation in which the criteria or constraints that define the
goal are satisfied is a goal state. Although some tasks can be accomplished with
a single action – to turn on the light, flip the switch – it is more common that
a task requires a sequence of actions. To open the window might require us to
draw the curtain, lift the latch, push the window outward, and secure the latch
again. Each action changes the material situation in some respect. A sequence
of actions A , A , A , …, A creates a sequence of situations, S , S , S …, S . Each
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