Input and output are separated by a duration of time, as in before and after, or past and present. In every feedback loop, as the name suggests, information about the result of a transformation or an action is sent back to the input of the system in the form of input data. If these new data facilitate and accelerate the transformation in the same direction as the preceding results, they are positive feedback - their effects are cumulative. If the new data produce a result in the opposite direction to previous results, they are negative feedback - their effects stabilize the system. However, when minus leads to another minus, events come to a standstill.
Typical examples are bankruptcy and economic depression.
In either case a positive feedback loop left to itself can lead only to the destruction of the system, through explosion or through the blocking of all its functions. This control is essential for a system to maintain itself in the course of time. In a negative loop every variation toward a plus triggers a correction toward the minus, and vice versa. A thermostat or a water tank equipped with a float are simple examples of regulation by negative feedback.