Residents of Hanoi, Vietnam enjoy car-free weekends in the area around the beautiful central lake of the city.

There is no new world that you make without the old world.
— Jane Jacobs

As I said in the introduction to this book, it is easy to focus on the problems of cities, and the ways they currently exacerbate the broader challenges that humanity faces. This book has focused instead on the powerful capacities that cities (and towns) already offer us, to help us to respond to those same challenges — and the hopeful signs all around us that we are beginning to learn these lessons, and to produce fruitful results. That is the young urban renaissance that is under way today.

It is also easy to attack the demagogic claims that have come to dominate our political environment in the last few years — for example the manifestly implausible idea that somehow building walls and excluding people will restore jobs and economic might. But I suggest it is more important to see the popularity of these claims in some quarters as the frustrated reaction to an equally deluded way of looking at urban economics, which supposes that growth comes solely from centralized stimulus and control. Hence if one group is not getting the goods from this centralized entity (be it big business, big government, or a complex of both) then it must be because another group is, and the only remedy is political revenge.

Both the action and the reaction are rooted in an older, more primitive industrial conception of the world — one that is now dangerously obsolete.

As we have explored, that is a carefully articulated message from the careers of both Jacobs and Alexander. Both of them have pointed to the intricate structural details of a more regenerative kind of city and its technologies, more rooted in the organized complexity of nature and the wholeness of natural systems, and more capable of achieving the kind of urban renaissance we need.

Jacobs reminds us that we must turn our attention away from silver bullets and magic formulas from afar or from above, and instead look within — to our own capacities and the capacities of our own neighborhoods and cities, to generate new growth and new wealth. We must refrain from expecting large quantities to be delivered up by large centralized entities, and start to work toward more polycentric economies, and more polycentric governance systems.

We have previously (in chapter I.2) discussed another very important implication, and it bears repeating here. Of course it is possible, up to a point, to replace the diversified, continuous public realm of urbanism, and the healthy catalytic growth it produces, with a system of segregated, machine-like capsules: automobiles, isolated offices and campuses, suburban housing monocultures, and the like. It is possible, in other words, to trade away a “natural human-capital city,” for an artificial kind of city that is nonetheless economically productive, at least in a historically limited and short-term sense. Indeed, we can see many examples of this kind of city around the world today.

However, this economic development can only be sustained with massive injections of resources — notably fossil fuels — whose limitations and negative impacts are only too obvious. Much of the economic growth that such a city produces is ultimately illusory, because it is consuming the basis of its own future growth. It is a kind of Ponzi scheme, the economic equivalent of “eating the seed corn.”

At the same time, we can certainly recognize that people in developing countries face a very difficult situation. We can understand and support the urgent need to alleviate poverty and improve health and quality of life — for children, for women, for vulnerable populations, and for humanity as a whole. As we have discussed, urbanization is indeed a powerful way of reducing disease and hunger, improving longevity, reducing population growth, increasing efficiency, and expanding opportunities for human development in myriad ways.

But it is a central conclusion of this book that not all urbanization is the same, and not all urbanism is the same. In the last century, we have made a kind of devil’s bargain with a quantitative approach that has failed to sufficiently account for the qualitative in urbanism. We have exploited economies of scale and standardization with great viral and metastatic power, but we have ignored economies of place and differentiation, to our great long-term detriment. As Jane Jacobs memorably put it, “we have left out feedback” — left out the proper accounting of externalities. As Christopher Alexander put it, we have failed to be sufficiently adaptive in our city-making — to human beings, to the qualitative aspects of life, and to the natural world on which we all ultimately depend.

The result of this maladaptive growth is a deep form of disorder, constituting a growing threat to the quality of our cities, and to our ultimate ability to sustain and prosper. The visible byproduct of this pathology is overall ugliness, with isolated elements of titillating beauty cloaked on here and there — like so much colorful product packaging, over a toxic industrial product.

This is not a trivial outcome. As Alexander suggests, beauty and ugliness are not “mere” psychological phenomena, but rather, manifestations of a deeper order, and of our own innate biological skill at detecting environmental order that will likely be beneficial to us, as well as its opposite. That helps explain why we hunger for beauty, in an almost literal sense. For that reason, the relation of this growing ugliness to a growing crisis of sustainability is not a coincidence. It is a biological warning signal, commanding our attention and response.

Both Alexander and Jacobs recognize the daunting challenges we face in the years ahead — ecological crises, resource crises, and at the heart of it, crises in our technological and cultural systems. They are certainly not alone in these concerns, or in the effort to offer constructive solutions. Their unique contribution, as this book has discussed, may be in the complementary structural outlines they have mapped out for us.

Quite intentionally, this book has not discussed the considerable criticisms that have been made of both Jacobs and Alexander. That is for another book, or perhaps many books. However, it is worth noting one persistent misunderstanding of both of them: that they are in the league of so many other designers and theorists who offer just more ex cathedra pronouncements, ideologically laden design theories, and assumptions that must be swallowed whole in cultish fashion. That is indeed a malady of much of the architecture and planning world today — but Jacobs and Alexander are critics from outside of it, not participants within it.

Indeed Jacobs was particularly withering in her criticism of professional ideology, declaring it a “pseudo-science” that “seems almost neurotic in its determination to imitate empiric failure and ignore empiric success.” Alexander for his part envisioned patterns as “falsifiable hypotheses,” and he acknowledged a strong influence from the empiricist philosopher of science Karl Popper. In fact, throughout his career, he showed a dogged concern with observation and reliable conclusion, and a repeated willingness to make major revisions in his conclusions when the evidence demanded it. (It was Alexander who, in the tenth anniversary of his book Notes on the Synthesis of Form, used its new preface to repudiate some of his own ideas in the book in light of subsequent evidence.)

In Alexander’s case, this empiricism was sometimes obscured by the poetic (some would say spiritual) quality of his writing, and his tenacious, sometimes pugnacious debating style with colleagues (one that is not uncommon among British empiricists, it should be noted). In Jacobs’ case, her methods of observation were only the first step in what could be considered a scientific method (as my colleague Stephen Marshall has noted) — but a remarkable and important first step it was.

Both authors leave us today free to test their ideas, to falsify, modify, combine with others — and then, if we find them useful, proceed to apply the ideas constructively, or alternatively, revise them as needed. Both authors have frequently urged us to follow an evidence-based approach, and continue the journey of learning and growth.

This book has argued that, very usefully, their ideas offer us a kind of working hypothesis, or pair of overlapping hypotheses, that offer “something to go on,” as all good science does. Most importantly, I think, they show us that an alternative path is available, and they provide detailed information about the structural nature of the changes needed. I have also argued that, partly as a result of their useful ideas, an urban renaissance is already beginning to be visible, and it awaits further development.

In that sense, they have both offered us a useful road map — and, I think, defined for us a critical choice.

This is the choice that we now face — and it is an increasingly urgent one. As discussed earlier, we are in an unprecedented era of urbanization, very likely producing more sheer area of urban fabric in the first half of the 21st Century than we have produced in all of human history. What will be the model, if not the old 20th Century “business as usual”? How will we transition to another, more durable kind of urbanism, rooted in a more durable kind of technology, economy and culture? How will we avert the catastrophic collapse that seems inevitable without changes to the current unsustainable path?

These are the broader questions that underlie the New Urban Agenda and its implementation, and that connect it to the Sustainable Development Goals, the Paris Agreement on Climate Change, and related initiatives. These are the urgent questions that underlie this young urban renaissance, and underscore its integral role in larger questions of human well-being.

As I asked in Chapter I.2, will we continue to stake our entire future on what I referred to as a kind of economic “crack cocaine high” — a quick and intense economic boost, followed by a planetary hangover — and meanwhile, allow our politics to devolve into ugly shouting matches over who gets the next fix? That way lies a “dark age ahead,” as Jacobs put it memorably in her last cautionary book.

Or will we apply the knowledge of how cities (and economies) really can work, at their best? Will we put cities and towns to work as engines of sustainable regeneration, taking the steps needed to unleash their powerful urban dynamics? Will we make the transition to what Jacobs called an “age of human capital?”

While much remains to be done, and this book only begins to explore some of the issues ahead, I think we can — and we must.