# Complex System There is no crisp definition of a complex system besides “it has emergent behavior that can’t be predicted by looking at its components” — so like AI and Robotics, it may be a “placeholder definition”. Are there systems that were once ‘complex’ but are now fully understood? <!-- #mental-model --> [Web URL for this note](http://notes.benjaminreinhardt.com/Complex+System) [Comment on this note](http://via.hypothes.is/http://notes.benjaminreinhardt.com/Complex+System)