A system is an open set of complementary, interacting parts, with properties, capabilities and behaviours of the set emerging both from the parts and… - Derek Hitchins

The motives for conceiving modern systems engineering are to be found, at least in part, in past disasters. Arthur D. Hall III cites: the chemical plant leakage in Bhopal (1986); the explosion of the NASA Challenger space shuttle (1986) and the Apollo fire (1967); the sinking of the Titanic (1912); the nuclear explosion in Chernobyl (1986) and the disaster at Three Mile Island power plant (1979). He cites, too, the capture of markets by Japan from the U.S., the decline in US productivity and the failure of the US secondary school system. He identifies the millions of people dying of starvation every year while other nations stockpile surplus food, medical disasters such as heart disease, while governments subsidize grains used to produce high cholesterol meat, milk and eggs; and many more. One implication is clear: systems engineering faces challenges well beyond the sphere of engineering.

The real world is made from open, interacting systems, behaving chaotically.

Emergence is the phenomenon of properties, capabilities and behaviours evident in the whole system that are not exclusively ascribable to any of its parts. Classic examples of emergence include: self awareness from the human brain; the pungent smell of ammonia emerging from two colorless, odorless gases-nitrogen and hydrogen; and so on.