Stafford Beer introduced the term POSIWID - the purpose of the system is what it does. This gives us a different perspective on a range of social and political issues. When we understand the complex loops that maintain the status quo, we are better equipped to make positive changes in organizations and society.
The POSIWID principle applies a kind of backwards logic to systems thinking. (This backwards logic is possibly a form of Peirce's abduction, but I haven't checked this properly.)
If a complex system produces a given outcome, or if a given outcome emerges from a complex system, then we may assume some purpose linked to this outcome.
This is a useful guide for investigation and interpretation. Ignore the official purpose of the system, ignore what the designers and custodians of a system say, and concentrate on its actual behaviour.
Conversely, if there is some unexplained pattern of behaviour, look for a system whose purpose this pattern reveals. (We often can't see the system directly, but we infer its hidden presence because this helps to make sense of some observed pattern of behaviour.)
The POSIWID blog is produced by Richard Veryard, with occasional contributions from friends who share a commitment to understanding systems.