To be a good builder, you need a feel for what surrounds you. Christopher Alexander knows.

Second of two parts on Christopher Alexander and a discussion of his four-volume book "The Nature of Order."

A 300-year-old willow tree stands behind the old farmhouse in which Christopher Alexander has lived for several years at the end of a road in West Sussex, England.

Look at the tree and your attention shuttles incessantly between its immensity and its shimmering details. You experience the "awakening of space" through the interplay of "centers" that Alexander movingly describes in various passages of his four-volume work "The Nature of Order." He sees this phenomenon as one that builders and other artists in traditional societies frequently understood and he believes that the modern world has lost that knowledge, to its detriment.

"The Nature of Order" attempts to give a practical and even a mathematical foundation to the interdependence of life and space that he initially cultivated intuitively in his work as architect and builder.

Alexander, 69, was born in Vienna and began academic life as a mathematical prodigy. He got a master's degree in mathematics at Cambridge University before switching to architecture, in which he earned a bachelor's degree at Cambridge and a doctorate at Harvard. During an incredibly productive career, he and his colleagues have designed private homes and public buildings on several continents.

He is currently working on a plan to close 30 percent of London's streets to automotive traffic and believes he can prove that this would improve traffic flow through the city.

In appendices to "The Nature of Order," Alexander attempts a rough mathematical definition -- which I am not competent to judge -- of the field of centers in physical space.

As a professor of architecture at UC Berkeley, Alexander frequently found himself in an embattled position as he openly exposed the disfigurement of large parts of the world by 20th century architecture.

Alexander's West Sussex house has the same sort of rumpled, hospitable informality as the man himself. He believes that the house's oldest interior walls date from the 15th century, its shell from the 18th. We sat before one of those antique inner walls -- a pleasingly irregular structure of dark timbers embedded in white plaster -- as we talked about "The Nature of Order."

In the books, Alexander takes great care to articulate the process that guides his practice, a process of feeling the subtle structure of a situation and letting simple, practical questions guide the "unfolding" of architectural form by an educated but nonanalytical responsiveness.

When he switched to architecture in his student years, Alexander recalled, "I decided I had to determine what this -- architecture -- is. So I said I'm going to start with very, very tiny stuff, where I could say 'I know this' ... what kind of things can I write down that I really know? Some were close to trivial, like 'wouldn't it be nice to have a shelf outside the front door so you can set down your packages while you look for your key?' Of course it's not truth, but at least you can say, 'that might be useful, it might be pleasant.' Anyway, it was the mid-'70s before I finished with the whole 'Pattern Language' story ("A Pattern Language," Oxford University Press). ... Then I realized that this stuff is great but when you start facing the question of form, it's too vague on that subject. So I started looking at the forms of things from the point of view of the impact of that form on us."

In Vol. 2 of "The Nature of Order" and frequently in conversation, he refers to "the thrall of images" that captivated architects in the past half-century or more.

"Images in the 20th century had a unique power," he writes, "where image became divorced from reality, and often more important than reality. ... Buildings were judged -- at least by members of our own profession -- more by the way they looked in magazines than by the satisfaction people felt when using them."

It took years of experience, Alexander said, before he reached the premise of "The Nature of Order": that the subtle structures he learned to detect "were really and truly things about the world -- shared and shareable -- and not just a cognitive phenomenon. That led to a reassertion of things that over the centuries many artists and philosophers have always known," especially in Vol. 4, subtitled "The Luminous Ground."

"Speaking as a builder," Alexander said, "if you start something, you must have a vision of the thing which arises from your instinct about preserving and enhancing what is there. ... If you're working correctly, the feeling doesn't wander about. If you have a feeling-vision of the thing -- a painting, a building, a garden, a piece of a neighborhood -- as long as you're very firmly anchored in your knowledge of that thing, and you can see it with your eyes closed, you can keep correcting your actions. ... It's not a question of holding onto every little detail, but of holding onto the feeling."

To skeptics of his methods he offers the following analogy: "There are some geologists involved with prospecting for oil and other hidden resources," he said, "who can pick up a rock and say, 'yes, there's oil under there.' A geologist who has been studying those kinds of rocks for 10 or 20 years is able to make that pronouncement. It isn't necessarily right, because we're all prone to error, but at least it's about something real -- whether that structure's there. That geologist has simply learned enough about the structure so that his ability to detect whether it's present or not is above average. It's really like that for the things I'm writing about, whether we're talking about artifacts from other times and cultures or whether it's a question of studying your own work and trying to determine whether you're going in the right direction. It's always this hopefully informed judgment about structure. If I'm working with clients, I try to bring them into that way of seeing things as far as I possibly can."

The astonishing willow tree outside the window led me to ask whether his long discussion of the power of centers might not encourage fellow architects to overload a building with centers.

"That's actually a weakness of the manuscript," he said. "When you make something, cleaning it out of structural debris is one of the most vital things you do. 'The void' " -- one of the 15 properties, or 15 ways that centers help each other come to life -- "says that you need large areas of nothing for the field of centers of play against. But somehow that's not the impression that comes across. If one were to think that it's all buzzing, you'd be only a step away from bric-a-brac, and that wouldn't help anything."

My interest in the virtual dimensions of artworks, from illusionistic space to intellectual content, led to the question of whether the field of centers extends to the realm of ideas, whether it might explain the nonrational power of certain ideas, alternative to, say, a psychoanalytic account.

"I'm convinced that the topic you raise is real," Alexander said. "Whether what I've done is deep enough to get into something like that, I don't know. The problem is we don't know what the domain of thoughts is, since we don't even have a clue as to how ideas exist as structures. ... I think even if one wasn't able to give pungent analysis, merely to ask the question and contemplate it -- which ideas have more life, which less, and can we agree about that? I think we probably would agree, with difficulty."

Then what about cyberspace, which engages more of people's time today than anyone would have thought possible a generation ago?

"Are we talking about virtual space in the sense of a CAD (computer-aided design) representation of walking through a building, which in the main I find fairly obnoxious?" Alexander asked. "I mean, making simulations of what you're going to build is tremendously useful if you can get feedback from them that will tell you where you've gone wrong and what you can do about it. My experience with CAD representations is that they give you none of that information, absolutely zero. It's strange actually.

"Anyway that's one kind of cyberspace, and then there's the space of wherever software lives. I'm not talking about in the machine, I'm talking about the domain of everything you can write as a piece of software -- that's a huge domain and I've often had discussions with computer scientists about it because it's not quite clear what that domain is. With 3D space you can imagine the range of what's possible."

To my surprise, at this point, Alexander brought up dreams.

"Dreams are in effect like cyberspace, with a slightly different interface," he said, "so I don't see something inherently negative about cyberspace at all. I do think we're in its infancy and therefore pretty clumsy with it, but more than that I'm worried about the following. ... The buildings that I build very often have a dreamlike reality. I don't mean by that they have a fantasy quality at all, in fact quite the reverse. They contain in some degree the ingredients that give dreams their power ... stuff that's very close to us. So dreams can make you wake up in a sweat or they can give you insight into a problem that's been bothering you for months. I think the reason is that the raw material is stuff that is very close to us. I'm not sure I'd want to say that that's what I try to do in a building."

But in fact, anyone who has entered one of Alexander's buildings will recognize its dreamlikeness in an improbable play of light, form, materials and proportions. The ones I have seen materialize feeling in a manner I associate with handmade works of art rather than contemporary buildings.