Evolution continually innovates, but at each level it conserves the elements that are recombined to yield the innovations.

Model building is the art of selecting those aspects of a process that are relevant to the question being asked. As with any art, this selection is guided by taste, elegance, and metaphor; it is a matter of induction, rather than deduction. High science depends on this art.

If we are to understand the interactions of a large number of agents, we must first be able to describe the capabilities of individual agents.

The multiplier effect is a major feature of networks and flows. It arises regardless of the particular nature of the resource, be it goods, money, or messages.

If there is to be a competition, there must be some basis for resolving it. It is also clear that the competition should be experienced based.

Evolution continually innovates, but at each level it conserves the elements that are recombined to yield the innovations.

This use of building blocks to generate internal models is a pervasive feature of complex adaptive systems.