- A system is more than the sum of its parts. It may exhibit adaptive, dynamic, goal-seeking, self-preserving, and sometimes evolutionary behavior. - _"You think that because you understand 'one' that you must therefore understand 'two' because one and one make two. But you forget that you must also understand 'and'."_ —Sufi teaching story - A system consists of: - elements - interconnections - functions and/or purposes - A function is *usually* used for a non-human system. - A purpose is *usually* used for a human one. - Many systems will have both human and non-human elements making the terms almost interchangeable.