I won’t claim that we succeeded in everything, but we did bring change where change seemed impossible. Things worked because people cooperated, and they did so because they were astonished at their own power. Hope that delivered results generated more hope. Show me a city with a thousand problems, and I’ll show you 10,000 people who can solve them.

When the city faced a critical water shortage, I made a public commitment: There would be no traditional rationing to manage the crisis, no cutting of supply. Instead, we set a goal of voluntary conservation of 12 to 20 percent; ultimately we achieved savings of 8 to 16 percent. To inform people of this policy, we replaced the busy signal on people’s telephones with a public message, either in my voice or that of the Colombian pop star Shakira, saying, “Thank you for saving water.”

We published information about how to save water, and many families discussed and devised their own options for reducing consumption. Even as we increased the provision of water and sanitation to nearly all households in Bogotá, water consumption went down. It remains lower today than before the crisis, thanks to the good practices that we stimulated.

This illustrates another lesson we learned. It helps to develop short, pleasing experiences for people that generate stories of delightful surprise, moments of mutual admiration among citizens and the welcome challenge of understanding something new. But then you need to consolidate those stories with good statistical results obtained through cold, rational measurement. That creates a virtuous cycle, so that congenial new experiences lead to statistically documented improvements, and the documentation raises expectations for more welcome change.

The art of politics is a curious business. It combines, as no other profession or occupation does, rigorous reasoning, sincere emotions and extroverted body language, with what are sometimes painfully cold, slow and planned strategic interactions. It is about leading, but not directing: What people love most is when you write on the blackboard a risky first half of a sentence and then recognize their freedom to write the other half.

My main theoretical and practical concern has been how to use the force of social and moral regulation to obtain the rule of law. This entailed a fundamental respect for human lives, expressed in the dictum “Life is sacred.” My purpose was to create a cosmopolitan culture of citizenship in which expressions like “crimes against humanity” would find a precise operational meaning.

Perhaps it’s time to look again at the law and its fraying fabric. My experience suggests that humanity is learning three ways of reducing the gap between the formal field of law and the informal realm of culture: a more creative enforcement of the law, the careful reform of the law itself, and the aesthetic exploration of the possibility of forms of empathy that can transcend national boundaries.