The purpose of a system is what it does

The purpose of a system is what it does (POSIWID) is a heuristic in systems thinking coined by the British management consultant Stafford Beer,^[1] who stated that there is "no point in claiming that the purpose of a system is to do what it constantly fails to do".^[2] It is widely used by systems theorists, and is generally invoked to counter the notion that the purpose of a system can be read from the intentions of those who design, operate or promote it. When a system's side effects or unintended consequences reveal that its behaviour is poorly understood, then the POSIWID perspective can balance political understandings of system behaviour with a more straightforwardly descriptive view.

Origins

Beer coined POSIWID in his books and used it many times in public addresses.^[3] Speaking to the University of Valladolid in October 2001, he said:^[1]

According to the cybernetician, the purpose of a system is what it does. This is a basic dictum. It stands for bald fact, which makes a better starting point in seeking understanding than the familiar attributions of good intention, prejudices about expectations, moral judgement, or sheer ignorance of circumstances.

Uses

From a cybernetic perspective, complex systems are not controllable by simple notions of management, and interventions in a system can best be understood by looking at how they affect observed system behaviour. The term is used in many other fields as well, including biology^[4] and management.^[5] Whereas a cybernetician may apply the principle to the results inexorably produced by the mechanical dynamics of an activity system, a management scientist may apply it to the results produced by the self-interest of actors who play roles in a business or other institution.

For example, if every time a person's cat gets eaten by a coyote, they simply replace it with a new cat from an animal sanctuary, then the purpose of that system is to feed shelter cats to coyotes. The system's purpose could be altered by measures such as keeping the cat indoors, or building a fence.

See also

• Duck test ("if it looks like a duck...")
• Emergence
• Form follows function
• Functionalism–intentionalism debate
• Hostile architecture
• Machine learning
• Noble lie
• Prefigurative politics
• Teleology
• The proof of the pudding is in the eating (at Wiktionary)
• Systemantics