Concept
Sensitive dependence, and the two unpredictabilities
Two different things stop a Global Form being predictable, and they ask for different responses, so the book keeps them apart. *Sensitive dependence*: the same deterministic rule from two starting states differing by less than anyone can measure, diverging at a rate that compounds — which is why forecasting has a horizon rather than an accuracy problem, and why measuring harder does not help. *Unenumerable rules*: derived from the Nest rather than imported, since a Global Form at one scale is a Local Rule at the next, so no boundary drawn around a system is real and what crosses it was never interference.
Where it appears
Treated in
- Part Four — The Ground UnderneathThe Limits of Running It ForwardFinding the rule is not predicting the form. Two things make a Global Form unpredictable, a named rule is only a hypothesis, and fatalism turns out to be unavailable rather than false.
- Part One — Why This MattersComplicated or ComplexA jet engine and a pond both have many parts. Only one of them has a feedback loop — and only a complex system can ever produce a Third Thing.