The evolution of property law is driven by an ongoing search for ways to internalize externalities: positive externalities associated with productive effort and negative externalities associated with misuse of commonly held resources. In theory, and sometimes in practice, responsibility is individualized and internalized over time. Increasingly, people pay for their own mistakes and misfortunes, and not for the mistakes and misfortunes of others.

It is this result that is most striking from a static perspective. It makes the whole idea of private property seem deeply offensive to some. The ideology surrounding private property is a celebration of strength, of will, of courage, of talent. That unflinchingly optimistic celebration of human excellence inspires some people and infuriates others. But neither the philosophy nor the historical reality is merely about praising human strengths. Each is also about giving people a chance to develop their strengths in the first place.

In some cases, though, people are born with no potential to support themselves. They have to hope to live in a society where their neighbors will be strong enough to carry those who cannot carry themselves. In other cases, people support themselves and even save for retirement in a market society but would be lost in a nonmarket setting. They do not need to be carried by neighbors, but they do need opportunities to trade for products they cannot make for themselves. Section 1.1.5 spoke of society as a cooperative venture for mutual advantage.