Of particular concern in cybernetic analysis are closed chains of causal influences or causal links. If the succession of causal influences tends to cancel out whatever condition triggered that succession, the chain is called a negative-feedback loop. For example, in the system depicted at right, a thermostat, set for a range of 66º-72º F, is attached to both an air conditioner and a heater. Any temperature fluctuation above or below the range triggers a negative-feedback loop, indicated by a chain of arrows and a minus sign, which tends to reverse or cancel that triggering fluctuation. In this and other systems, negative-feedback loops often contribute to stability or homeostasis, by constantly restoring the system to a state of equilibrium. We have already encountered such negative-feedback loops in our analysis of the free market, where they preserve the equilibrium between supply and demand (see graphs on pp. 4.6:18, 4.6:20).

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