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The Growth of Competence 181

Figure 6.2. A goal-subgoal hierarchy for using an elevator. Goals are symbolized by
circles and actions by rectangles. This plan is implemented by the rules in table 6.1.

situation is the output of the action applied to its predecessor and serves as the
input to the immediately following action. A situation in which the goal has
not been satisfied but the person must stop pursuing it anyway due to lack of
time or other resources is a dead-end state.
in each successive state of affairs, the person has to choose which action to
perform. The initial state and the person’s repertoire of actions define a situation
tree. The latter includes all the situations that can be accomplished by applying
some action to the initial state S ; then all the situations that can be reached by
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doing the same to each of its descendants; and so on. A situation tree is neither
objective nor subjective but emerges in the interaction between a person and his
material environment. The person contributes the set of actions and the objec-
tive environment contributes the set of causal laws that determine the conse-
quences of those actions and hence the possible successors to each situation.
it is convenient to depict situation trees graphically. A graph of a situation
tree has a single root node, the initial situation, and paths branching off from
each other, ending in leaf nodes that are either dead-end states or goal states;
see Figure 3.3. Such a graph is a description of the task environment in terms
of the action possibilities it affords. to describe the person’s behavior as a path