The Law of Requisite Variety states: **only variety can absorb variety**. A regulator of a system can only regulate if the variety disposed by the regulator is equal to the variety generated by the reguland. Variety regulation can be one-one, such as the players on a soccer team, or it can be one-many, such as a king and his subjects. **Most regulation of variety, however, does not proceed from authority but from convention**. Traffic flow, for instance, is mostly regulated by two conventions: that traffic going in one direction will stay on one side of the road leaving the other side clear for traffic going in the opposite direction, and that traffic will stop on the red light and move on the green light. Ashby said "In its elementary forms the law is intuitively obvious and hardly deserving statement. Where the law, in its quantitative form, develops its power is when we come to consider a system in which these matters are not so obvious ...when it is very large... (or) much **too complex to be handled by unaided intuition**."
# SOURCE Ashby, W. R. (1956). Introduction to Cybernetics. London: Meuthen & Company.
# EXAMPLES • the number of laws governing an activity • the countering moves in a game • the need to match players on a football team with their opponents • the maintenance schedule for a plant
# NON-EXAMPLES • the capacity of the human brain to handle more than seven (plus or minus two) discrete items of information • the behavior of a policeman at a traffic intersection when he cannot see the build-up ahead • the attempt to control the economy through the banks or the money supply • acts of multinational firms in the absence of international law • the infection of a body by a new microorganism
# SEE Conant-Ashby Theorem; Game Theory; Model; Metasystem