ABSTRACT
Control systems theory provides a general framework for analyzing a wide range of goal-directed systems. The terminology used here is based on the work of McFarland (1971). A relatively simple example of an inanimate goal-directed system is a house’s heating system. The goal of the heating system is to keep the house temperature above some minimum level, say 65°F. If the house temperature drops below 65°F, the heating system “spontaneously” springs into action, starting the furnace. Once the temperature goal is reached, the activity of the heating system ceases. Of course, we know there is nothing magical about this process. The activity of the heating system is controlled by the thermostat, which relies on the fact that metals expand when heated and contract when cooled. The cooling of the metals in the thermostat causes them to bend and close an electrical switch, thus starting the furnace. Heating of the metals opens the switch and stops the furnace.
